linux/ipc/sem.c
Eric W. Biederman 51d6f2635b ipc/sem: Fix semctl(..., GETPID, ...) between pid namespaces
Today the last process to update a semaphore is remembered and
reported in the pid namespace of that process.  If there are processes
in any other pid namespace querying that process id with GETPID the
result will be unusable nonsense as it does not make any
sense in your own pid namespace.

Due to ipc_update_pid I don't think you will be able to get System V
ipc semaphores into a troublesome cache line ping-pong.  Using struct
pids from separate process are not a problem because they do not share
a cache line.  Using struct pid from different threads of the same
process are unlikely to be a problem as the reference count update
can be avoided.

Further linux futexes are a much better tool for the job of mutual
exclusion between processes than System V semaphores.  So I expect
programs that  are performance limited by their interprocess mutual
exclusion primitive will be using futexes.

So while it is possible that enhancing the storage of the last
rocess of a System V semaphore from an integer to a struct pid
will cause a performance regression because of the effect
of frequently updating the pid reference count.  I don't expect
that to happen in practice.

This change updates semctl(..., GETPID, ...) to return the
process id of the last process to update a semphore inthe
pid namespace of the calling process.

Fixes: b488893a39 ("pid namespaces: changes to show virtual ids to user")
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
2018-03-27 15:53:55 -05:00

2373 lines
60 KiB
C

// SPDX-License-Identifier: GPL-2.0
/*
* linux/ipc/sem.c
* Copyright (C) 1992 Krishna Balasubramanian
* Copyright (C) 1995 Eric Schenk, Bruno Haible
*
* /proc/sysvipc/sem support (c) 1999 Dragos Acostachioaie <dragos@iname.com>
*
* SMP-threaded, sysctl's added
* (c) 1999 Manfred Spraul <manfred@colorfullife.com>
* Enforced range limit on SEM_UNDO
* (c) 2001 Red Hat Inc
* Lockless wakeup
* (c) 2003 Manfred Spraul <manfred@colorfullife.com>
* (c) 2016 Davidlohr Bueso <dave@stgolabs.net>
* Further wakeup optimizations, documentation
* (c) 2010 Manfred Spraul <manfred@colorfullife.com>
*
* support for audit of ipc object properties and permission changes
* Dustin Kirkland <dustin.kirkland@us.ibm.com>
*
* namespaces support
* OpenVZ, SWsoft Inc.
* Pavel Emelianov <xemul@openvz.org>
*
* Implementation notes: (May 2010)
* This file implements System V semaphores.
*
* User space visible behavior:
* - FIFO ordering for semop() operations (just FIFO, not starvation
* protection)
* - multiple semaphore operations that alter the same semaphore in
* one semop() are handled.
* - sem_ctime (time of last semctl()) is updated in the IPC_SET, SETVAL and
* SETALL calls.
* - two Linux specific semctl() commands: SEM_STAT, SEM_INFO.
* - undo adjustments at process exit are limited to 0..SEMVMX.
* - namespace are supported.
* - SEMMSL, SEMMNS, SEMOPM and SEMMNI can be configured at runtine by writing
* to /proc/sys/kernel/sem.
* - statistics about the usage are reported in /proc/sysvipc/sem.
*
* Internals:
* - scalability:
* - all global variables are read-mostly.
* - semop() calls and semctl(RMID) are synchronized by RCU.
* - most operations do write operations (actually: spin_lock calls) to
* the per-semaphore array structure.
* Thus: Perfect SMP scaling between independent semaphore arrays.
* If multiple semaphores in one array are used, then cache line
* trashing on the semaphore array spinlock will limit the scaling.
* - semncnt and semzcnt are calculated on demand in count_semcnt()
* - the task that performs a successful semop() scans the list of all
* sleeping tasks and completes any pending operations that can be fulfilled.
* Semaphores are actively given to waiting tasks (necessary for FIFO).
* (see update_queue())
* - To improve the scalability, the actual wake-up calls are performed after
* dropping all locks. (see wake_up_sem_queue_prepare())
* - All work is done by the waker, the woken up task does not have to do
* anything - not even acquiring a lock or dropping a refcount.
* - A woken up task may not even touch the semaphore array anymore, it may
* have been destroyed already by a semctl(RMID).
* - UNDO values are stored in an array (one per process and per
* semaphore array, lazily allocated). For backwards compatibility, multiple
* modes for the UNDO variables are supported (per process, per thread)
* (see copy_semundo, CLONE_SYSVSEM)
* - There are two lists of the pending operations: a per-array list
* and per-semaphore list (stored in the array). This allows to achieve FIFO
* ordering without always scanning all pending operations.
* The worst-case behavior is nevertheless O(N^2) for N wakeups.
*/
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/init.h>
#include <linux/proc_fs.h>
#include <linux/time.h>
#include <linux/security.h>
#include <linux/syscalls.h>
#include <linux/audit.h>
#include <linux/capability.h>
#include <linux/seq_file.h>
#include <linux/rwsem.h>
#include <linux/nsproxy.h>
#include <linux/ipc_namespace.h>
#include <linux/sched/wake_q.h>
#include <linux/uaccess.h>
#include "util.h"
/* One semaphore structure for each semaphore in the system. */
struct sem {
int semval; /* current value */
/*
* PID of the process that last modified the semaphore. For
* Linux, specifically these are:
* - semop
* - semctl, via SETVAL and SETALL.
* - at task exit when performing undo adjustments (see exit_sem).
*/
struct pid *sempid;
spinlock_t lock; /* spinlock for fine-grained semtimedop */
struct list_head pending_alter; /* pending single-sop operations */
/* that alter the semaphore */
struct list_head pending_const; /* pending single-sop operations */
/* that do not alter the semaphore*/
time_t sem_otime; /* candidate for sem_otime */
} ____cacheline_aligned_in_smp;
/* One sem_array data structure for each set of semaphores in the system. */
struct sem_array {
struct kern_ipc_perm sem_perm; /* permissions .. see ipc.h */
time64_t sem_ctime; /* create/last semctl() time */
struct list_head pending_alter; /* pending operations */
/* that alter the array */
struct list_head pending_const; /* pending complex operations */
/* that do not alter semvals */
struct list_head list_id; /* undo requests on this array */
int sem_nsems; /* no. of semaphores in array */
int complex_count; /* pending complex operations */
unsigned int use_global_lock;/* >0: global lock required */
struct sem sems[];
} __randomize_layout;
/* One queue for each sleeping process in the system. */
struct sem_queue {
struct list_head list; /* queue of pending operations */
struct task_struct *sleeper; /* this process */
struct sem_undo *undo; /* undo structure */
struct pid *pid; /* process id of requesting process */
int status; /* completion status of operation */
struct sembuf *sops; /* array of pending operations */
struct sembuf *blocking; /* the operation that blocked */
int nsops; /* number of operations */
bool alter; /* does *sops alter the array? */
bool dupsop; /* sops on more than one sem_num */
};
/* Each task has a list of undo requests. They are executed automatically
* when the process exits.
*/
struct sem_undo {
struct list_head list_proc; /* per-process list: *
* all undos from one process
* rcu protected */
struct rcu_head rcu; /* rcu struct for sem_undo */
struct sem_undo_list *ulp; /* back ptr to sem_undo_list */
struct list_head list_id; /* per semaphore array list:
* all undos for one array */
int semid; /* semaphore set identifier */
short *semadj; /* array of adjustments */
/* one per semaphore */
};
/* sem_undo_list controls shared access to the list of sem_undo structures
* that may be shared among all a CLONE_SYSVSEM task group.
*/
struct sem_undo_list {
refcount_t refcnt;
spinlock_t lock;
struct list_head list_proc;
};
#define sem_ids(ns) ((ns)->ids[IPC_SEM_IDS])
static int newary(struct ipc_namespace *, struct ipc_params *);
static void freeary(struct ipc_namespace *, struct kern_ipc_perm *);
#ifdef CONFIG_PROC_FS
static int sysvipc_sem_proc_show(struct seq_file *s, void *it);
#endif
#define SEMMSL_FAST 256 /* 512 bytes on stack */
#define SEMOPM_FAST 64 /* ~ 372 bytes on stack */
/*
* Switching from the mode suitable for simple ops
* to the mode for complex ops is costly. Therefore:
* use some hysteresis
*/
#define USE_GLOBAL_LOCK_HYSTERESIS 10
/*
* Locking:
* a) global sem_lock() for read/write
* sem_undo.id_next,
* sem_array.complex_count,
* sem_array.pending{_alter,_const},
* sem_array.sem_undo
*
* b) global or semaphore sem_lock() for read/write:
* sem_array.sems[i].pending_{const,alter}:
*
* c) special:
* sem_undo_list.list_proc:
* * undo_list->lock for write
* * rcu for read
* use_global_lock:
* * global sem_lock() for write
* * either local or global sem_lock() for read.
*
* Memory ordering:
* Most ordering is enforced by using spin_lock() and spin_unlock().
* The special case is use_global_lock:
* Setting it from non-zero to 0 is a RELEASE, this is ensured by
* using smp_store_release().
* Testing if it is non-zero is an ACQUIRE, this is ensured by using
* smp_load_acquire().
* Setting it from 0 to non-zero must be ordered with regards to
* this smp_load_acquire(), this is guaranteed because the smp_load_acquire()
* is inside a spin_lock() and after a write from 0 to non-zero a
* spin_lock()+spin_unlock() is done.
*/
#define sc_semmsl sem_ctls[0]
#define sc_semmns sem_ctls[1]
#define sc_semopm sem_ctls[2]
#define sc_semmni sem_ctls[3]
int sem_init_ns(struct ipc_namespace *ns)
{
ns->sc_semmsl = SEMMSL;
ns->sc_semmns = SEMMNS;
ns->sc_semopm = SEMOPM;
ns->sc_semmni = SEMMNI;
ns->used_sems = 0;
return ipc_init_ids(&ns->ids[IPC_SEM_IDS]);
}
#ifdef CONFIG_IPC_NS
void sem_exit_ns(struct ipc_namespace *ns)
{
free_ipcs(ns, &sem_ids(ns), freeary);
idr_destroy(&ns->ids[IPC_SEM_IDS].ipcs_idr);
rhashtable_destroy(&ns->ids[IPC_SEM_IDS].key_ht);
}
#endif
int __init sem_init(void)
{
const int err = sem_init_ns(&init_ipc_ns);
ipc_init_proc_interface("sysvipc/sem",
" key semid perms nsems uid gid cuid cgid otime ctime\n",
IPC_SEM_IDS, sysvipc_sem_proc_show);
return err;
}
/**
* unmerge_queues - unmerge queues, if possible.
* @sma: semaphore array
*
* The function unmerges the wait queues if complex_count is 0.
* It must be called prior to dropping the global semaphore array lock.
*/
static void unmerge_queues(struct sem_array *sma)
{
struct sem_queue *q, *tq;
/* complex operations still around? */
if (sma->complex_count)
return;
/*
* We will switch back to simple mode.
* Move all pending operation back into the per-semaphore
* queues.
*/
list_for_each_entry_safe(q, tq, &sma->pending_alter, list) {
struct sem *curr;
curr = &sma->sems[q->sops[0].sem_num];
list_add_tail(&q->list, &curr->pending_alter);
}
INIT_LIST_HEAD(&sma->pending_alter);
}
/**
* merge_queues - merge single semop queues into global queue
* @sma: semaphore array
*
* This function merges all per-semaphore queues into the global queue.
* It is necessary to achieve FIFO ordering for the pending single-sop
* operations when a multi-semop operation must sleep.
* Only the alter operations must be moved, the const operations can stay.
*/
static void merge_queues(struct sem_array *sma)
{
int i;
for (i = 0; i < sma->sem_nsems; i++) {
struct sem *sem = &sma->sems[i];
list_splice_init(&sem->pending_alter, &sma->pending_alter);
}
}
static void sem_rcu_free(struct rcu_head *head)
{
struct kern_ipc_perm *p = container_of(head, struct kern_ipc_perm, rcu);
struct sem_array *sma = container_of(p, struct sem_array, sem_perm);
security_sem_free(&sma->sem_perm);
kvfree(sma);
}
/*
* Enter the mode suitable for non-simple operations:
* Caller must own sem_perm.lock.
*/
static void complexmode_enter(struct sem_array *sma)
{
int i;
struct sem *sem;
if (sma->use_global_lock > 0) {
/*
* We are already in global lock mode.
* Nothing to do, just reset the
* counter until we return to simple mode.
*/
sma->use_global_lock = USE_GLOBAL_LOCK_HYSTERESIS;
return;
}
sma->use_global_lock = USE_GLOBAL_LOCK_HYSTERESIS;
for (i = 0; i < sma->sem_nsems; i++) {
sem = &sma->sems[i];
spin_lock(&sem->lock);
spin_unlock(&sem->lock);
}
}
/*
* Try to leave the mode that disallows simple operations:
* Caller must own sem_perm.lock.
*/
static void complexmode_tryleave(struct sem_array *sma)
{
if (sma->complex_count) {
/* Complex ops are sleeping.
* We must stay in complex mode
*/
return;
}
if (sma->use_global_lock == 1) {
/*
* Immediately after setting use_global_lock to 0,
* a simple op can start. Thus: all memory writes
* performed by the current operation must be visible
* before we set use_global_lock to 0.
*/
smp_store_release(&sma->use_global_lock, 0);
} else {
sma->use_global_lock--;
}
}
#define SEM_GLOBAL_LOCK (-1)
/*
* If the request contains only one semaphore operation, and there are
* no complex transactions pending, lock only the semaphore involved.
* Otherwise, lock the entire semaphore array, since we either have
* multiple semaphores in our own semops, or we need to look at
* semaphores from other pending complex operations.
*/
static inline int sem_lock(struct sem_array *sma, struct sembuf *sops,
int nsops)
{
struct sem *sem;
if (nsops != 1) {
/* Complex operation - acquire a full lock */
ipc_lock_object(&sma->sem_perm);
/* Prevent parallel simple ops */
complexmode_enter(sma);
return SEM_GLOBAL_LOCK;
}
/*
* Only one semaphore affected - try to optimize locking.
* Optimized locking is possible if no complex operation
* is either enqueued or processed right now.
*
* Both facts are tracked by use_global_mode.
*/
sem = &sma->sems[sops->sem_num];
/*
* Initial check for use_global_lock. Just an optimization,
* no locking, no memory barrier.
*/
if (!sma->use_global_lock) {
/*
* It appears that no complex operation is around.
* Acquire the per-semaphore lock.
*/
spin_lock(&sem->lock);
/* pairs with smp_store_release() */
if (!smp_load_acquire(&sma->use_global_lock)) {
/* fast path successful! */
return sops->sem_num;
}
spin_unlock(&sem->lock);
}
/* slow path: acquire the full lock */
ipc_lock_object(&sma->sem_perm);
if (sma->use_global_lock == 0) {
/*
* The use_global_lock mode ended while we waited for
* sma->sem_perm.lock. Thus we must switch to locking
* with sem->lock.
* Unlike in the fast path, there is no need to recheck
* sma->use_global_lock after we have acquired sem->lock:
* We own sma->sem_perm.lock, thus use_global_lock cannot
* change.
*/
spin_lock(&sem->lock);
ipc_unlock_object(&sma->sem_perm);
return sops->sem_num;
} else {
/*
* Not a false alarm, thus continue to use the global lock
* mode. No need for complexmode_enter(), this was done by
* the caller that has set use_global_mode to non-zero.
*/
return SEM_GLOBAL_LOCK;
}
}
static inline void sem_unlock(struct sem_array *sma, int locknum)
{
if (locknum == SEM_GLOBAL_LOCK) {
unmerge_queues(sma);
complexmode_tryleave(sma);
ipc_unlock_object(&sma->sem_perm);
} else {
struct sem *sem = &sma->sems[locknum];
spin_unlock(&sem->lock);
}
}
/*
* sem_lock_(check_) routines are called in the paths where the rwsem
* is not held.
*
* The caller holds the RCU read lock.
*/
static inline struct sem_array *sem_obtain_object(struct ipc_namespace *ns, int id)
{
struct kern_ipc_perm *ipcp = ipc_obtain_object_idr(&sem_ids(ns), id);
if (IS_ERR(ipcp))
return ERR_CAST(ipcp);
return container_of(ipcp, struct sem_array, sem_perm);
}
static inline struct sem_array *sem_obtain_object_check(struct ipc_namespace *ns,
int id)
{
struct kern_ipc_perm *ipcp = ipc_obtain_object_check(&sem_ids(ns), id);
if (IS_ERR(ipcp))
return ERR_CAST(ipcp);
return container_of(ipcp, struct sem_array, sem_perm);
}
static inline void sem_lock_and_putref(struct sem_array *sma)
{
sem_lock(sma, NULL, -1);
ipc_rcu_putref(&sma->sem_perm, sem_rcu_free);
}
static inline void sem_rmid(struct ipc_namespace *ns, struct sem_array *s)
{
ipc_rmid(&sem_ids(ns), &s->sem_perm);
}
static struct sem_array *sem_alloc(size_t nsems)
{
struct sem_array *sma;
size_t size;
if (nsems > (INT_MAX - sizeof(*sma)) / sizeof(sma->sems[0]))
return NULL;
size = sizeof(*sma) + nsems * sizeof(sma->sems[0]);
sma = kvmalloc(size, GFP_KERNEL);
if (unlikely(!sma))
return NULL;
memset(sma, 0, size);
return sma;
}
/**
* newary - Create a new semaphore set
* @ns: namespace
* @params: ptr to the structure that contains key, semflg and nsems
*
* Called with sem_ids.rwsem held (as a writer)
*/
static int newary(struct ipc_namespace *ns, struct ipc_params *params)
{
int retval;
struct sem_array *sma;
key_t key = params->key;
int nsems = params->u.nsems;
int semflg = params->flg;
int i;
if (!nsems)
return -EINVAL;
if (ns->used_sems + nsems > ns->sc_semmns)
return -ENOSPC;
sma = sem_alloc(nsems);
if (!sma)
return -ENOMEM;
sma->sem_perm.mode = (semflg & S_IRWXUGO);
sma->sem_perm.key = key;
sma->sem_perm.security = NULL;
retval = security_sem_alloc(&sma->sem_perm);
if (retval) {
kvfree(sma);
return retval;
}
for (i = 0; i < nsems; i++) {
INIT_LIST_HEAD(&sma->sems[i].pending_alter);
INIT_LIST_HEAD(&sma->sems[i].pending_const);
spin_lock_init(&sma->sems[i].lock);
}
sma->complex_count = 0;
sma->use_global_lock = USE_GLOBAL_LOCK_HYSTERESIS;
INIT_LIST_HEAD(&sma->pending_alter);
INIT_LIST_HEAD(&sma->pending_const);
INIT_LIST_HEAD(&sma->list_id);
sma->sem_nsems = nsems;
sma->sem_ctime = ktime_get_real_seconds();
/* ipc_addid() locks sma upon success. */
retval = ipc_addid(&sem_ids(ns), &sma->sem_perm, ns->sc_semmni);
if (retval < 0) {
call_rcu(&sma->sem_perm.rcu, sem_rcu_free);
return retval;
}
ns->used_sems += nsems;
sem_unlock(sma, -1);
rcu_read_unlock();
return sma->sem_perm.id;
}
/*
* Called with sem_ids.rwsem and ipcp locked.
*/
static inline int sem_security(struct kern_ipc_perm *ipcp, int semflg)
{
return security_sem_associate(ipcp, semflg);
}
/*
* Called with sem_ids.rwsem and ipcp locked.
*/
static inline int sem_more_checks(struct kern_ipc_perm *ipcp,
struct ipc_params *params)
{
struct sem_array *sma;
sma = container_of(ipcp, struct sem_array, sem_perm);
if (params->u.nsems > sma->sem_nsems)
return -EINVAL;
return 0;
}
SYSCALL_DEFINE3(semget, key_t, key, int, nsems, int, semflg)
{
struct ipc_namespace *ns;
static const struct ipc_ops sem_ops = {
.getnew = newary,
.associate = sem_security,
.more_checks = sem_more_checks,
};
struct ipc_params sem_params;
ns = current->nsproxy->ipc_ns;
if (nsems < 0 || nsems > ns->sc_semmsl)
return -EINVAL;
sem_params.key = key;
sem_params.flg = semflg;
sem_params.u.nsems = nsems;
return ipcget(ns, &sem_ids(ns), &sem_ops, &sem_params);
}
/**
* perform_atomic_semop[_slow] - Attempt to perform semaphore
* operations on a given array.
* @sma: semaphore array
* @q: struct sem_queue that describes the operation
*
* Caller blocking are as follows, based the value
* indicated by the semaphore operation (sem_op):
*
* (1) >0 never blocks.
* (2) 0 (wait-for-zero operation): semval is non-zero.
* (3) <0 attempting to decrement semval to a value smaller than zero.
*
* Returns 0 if the operation was possible.
* Returns 1 if the operation is impossible, the caller must sleep.
* Returns <0 for error codes.
*/
static int perform_atomic_semop_slow(struct sem_array *sma, struct sem_queue *q)
{
int result, sem_op, nsops;
struct pid *pid;
struct sembuf *sop;
struct sem *curr;
struct sembuf *sops;
struct sem_undo *un;
sops = q->sops;
nsops = q->nsops;
un = q->undo;
for (sop = sops; sop < sops + nsops; sop++) {
curr = &sma->sems[sop->sem_num];
sem_op = sop->sem_op;
result = curr->semval;
if (!sem_op && result)
goto would_block;
result += sem_op;
if (result < 0)
goto would_block;
if (result > SEMVMX)
goto out_of_range;
if (sop->sem_flg & SEM_UNDO) {
int undo = un->semadj[sop->sem_num] - sem_op;
/* Exceeding the undo range is an error. */
if (undo < (-SEMAEM - 1) || undo > SEMAEM)
goto out_of_range;
un->semadj[sop->sem_num] = undo;
}
curr->semval = result;
}
sop--;
pid = q->pid;
while (sop >= sops) {
ipc_update_pid(&sma->sems[sop->sem_num].sempid, pid);
sop--;
}
return 0;
out_of_range:
result = -ERANGE;
goto undo;
would_block:
q->blocking = sop;
if (sop->sem_flg & IPC_NOWAIT)
result = -EAGAIN;
else
result = 1;
undo:
sop--;
while (sop >= sops) {
sem_op = sop->sem_op;
sma->sems[sop->sem_num].semval -= sem_op;
if (sop->sem_flg & SEM_UNDO)
un->semadj[sop->sem_num] += sem_op;
sop--;
}
return result;
}
static int perform_atomic_semop(struct sem_array *sma, struct sem_queue *q)
{
int result, sem_op, nsops;
struct sembuf *sop;
struct sem *curr;
struct sembuf *sops;
struct sem_undo *un;
sops = q->sops;
nsops = q->nsops;
un = q->undo;
if (unlikely(q->dupsop))
return perform_atomic_semop_slow(sma, q);
/*
* We scan the semaphore set twice, first to ensure that the entire
* operation can succeed, therefore avoiding any pointless writes
* to shared memory and having to undo such changes in order to block
* until the operations can go through.
*/
for (sop = sops; sop < sops + nsops; sop++) {
curr = &sma->sems[sop->sem_num];
sem_op = sop->sem_op;
result = curr->semval;
if (!sem_op && result)
goto would_block; /* wait-for-zero */
result += sem_op;
if (result < 0)
goto would_block;
if (result > SEMVMX)
return -ERANGE;
if (sop->sem_flg & SEM_UNDO) {
int undo = un->semadj[sop->sem_num] - sem_op;
/* Exceeding the undo range is an error. */
if (undo < (-SEMAEM - 1) || undo > SEMAEM)
return -ERANGE;
}
}
for (sop = sops; sop < sops + nsops; sop++) {
curr = &sma->sems[sop->sem_num];
sem_op = sop->sem_op;
result = curr->semval;
if (sop->sem_flg & SEM_UNDO) {
int undo = un->semadj[sop->sem_num] - sem_op;
un->semadj[sop->sem_num] = undo;
}
curr->semval += sem_op;
ipc_update_pid(&curr->sempid, q->pid);
}
return 0;
would_block:
q->blocking = sop;
return sop->sem_flg & IPC_NOWAIT ? -EAGAIN : 1;
}
static inline void wake_up_sem_queue_prepare(struct sem_queue *q, int error,
struct wake_q_head *wake_q)
{
wake_q_add(wake_q, q->sleeper);
/*
* Rely on the above implicit barrier, such that we can
* ensure that we hold reference to the task before setting
* q->status. Otherwise we could race with do_exit if the
* task is awoken by an external event before calling
* wake_up_process().
*/
WRITE_ONCE(q->status, error);
}
static void unlink_queue(struct sem_array *sma, struct sem_queue *q)
{
list_del(&q->list);
if (q->nsops > 1)
sma->complex_count--;
}
/** check_restart(sma, q)
* @sma: semaphore array
* @q: the operation that just completed
*
* update_queue is O(N^2) when it restarts scanning the whole queue of
* waiting operations. Therefore this function checks if the restart is
* really necessary. It is called after a previously waiting operation
* modified the array.
* Note that wait-for-zero operations are handled without restart.
*/
static inline int check_restart(struct sem_array *sma, struct sem_queue *q)
{
/* pending complex alter operations are too difficult to analyse */
if (!list_empty(&sma->pending_alter))
return 1;
/* we were a sleeping complex operation. Too difficult */
if (q->nsops > 1)
return 1;
/* It is impossible that someone waits for the new value:
* - complex operations always restart.
* - wait-for-zero are handled seperately.
* - q is a previously sleeping simple operation that
* altered the array. It must be a decrement, because
* simple increments never sleep.
* - If there are older (higher priority) decrements
* in the queue, then they have observed the original
* semval value and couldn't proceed. The operation
* decremented to value - thus they won't proceed either.
*/
return 0;
}
/**
* wake_const_ops - wake up non-alter tasks
* @sma: semaphore array.
* @semnum: semaphore that was modified.
* @wake_q: lockless wake-queue head.
*
* wake_const_ops must be called after a semaphore in a semaphore array
* was set to 0. If complex const operations are pending, wake_const_ops must
* be called with semnum = -1, as well as with the number of each modified
* semaphore.
* The tasks that must be woken up are added to @wake_q. The return code
* is stored in q->pid.
* The function returns 1 if at least one operation was completed successfully.
*/
static int wake_const_ops(struct sem_array *sma, int semnum,
struct wake_q_head *wake_q)
{
struct sem_queue *q, *tmp;
struct list_head *pending_list;
int semop_completed = 0;
if (semnum == -1)
pending_list = &sma->pending_const;
else
pending_list = &sma->sems[semnum].pending_const;
list_for_each_entry_safe(q, tmp, pending_list, list) {
int error = perform_atomic_semop(sma, q);
if (error > 0)
continue;
/* operation completed, remove from queue & wakeup */
unlink_queue(sma, q);
wake_up_sem_queue_prepare(q, error, wake_q);
if (error == 0)
semop_completed = 1;
}
return semop_completed;
}
/**
* do_smart_wakeup_zero - wakeup all wait for zero tasks
* @sma: semaphore array
* @sops: operations that were performed
* @nsops: number of operations
* @wake_q: lockless wake-queue head
*
* Checks all required queue for wait-for-zero operations, based
* on the actual changes that were performed on the semaphore array.
* The function returns 1 if at least one operation was completed successfully.
*/
static int do_smart_wakeup_zero(struct sem_array *sma, struct sembuf *sops,
int nsops, struct wake_q_head *wake_q)
{
int i;
int semop_completed = 0;
int got_zero = 0;
/* first: the per-semaphore queues, if known */
if (sops) {
for (i = 0; i < nsops; i++) {
int num = sops[i].sem_num;
if (sma->sems[num].semval == 0) {
got_zero = 1;
semop_completed |= wake_const_ops(sma, num, wake_q);
}
}
} else {
/*
* No sops means modified semaphores not known.
* Assume all were changed.
*/
for (i = 0; i < sma->sem_nsems; i++) {
if (sma->sems[i].semval == 0) {
got_zero = 1;
semop_completed |= wake_const_ops(sma, i, wake_q);
}
}
}
/*
* If one of the modified semaphores got 0,
* then check the global queue, too.
*/
if (got_zero)
semop_completed |= wake_const_ops(sma, -1, wake_q);
return semop_completed;
}
/**
* update_queue - look for tasks that can be completed.
* @sma: semaphore array.
* @semnum: semaphore that was modified.
* @wake_q: lockless wake-queue head.
*
* update_queue must be called after a semaphore in a semaphore array
* was modified. If multiple semaphores were modified, update_queue must
* be called with semnum = -1, as well as with the number of each modified
* semaphore.
* The tasks that must be woken up are added to @wake_q. The return code
* is stored in q->pid.
* The function internally checks if const operations can now succeed.
*
* The function return 1 if at least one semop was completed successfully.
*/
static int update_queue(struct sem_array *sma, int semnum, struct wake_q_head *wake_q)
{
struct sem_queue *q, *tmp;
struct list_head *pending_list;
int semop_completed = 0;
if (semnum == -1)
pending_list = &sma->pending_alter;
else
pending_list = &sma->sems[semnum].pending_alter;
again:
list_for_each_entry_safe(q, tmp, pending_list, list) {
int error, restart;
/* If we are scanning the single sop, per-semaphore list of
* one semaphore and that semaphore is 0, then it is not
* necessary to scan further: simple increments
* that affect only one entry succeed immediately and cannot
* be in the per semaphore pending queue, and decrements
* cannot be successful if the value is already 0.
*/
if (semnum != -1 && sma->sems[semnum].semval == 0)
break;
error = perform_atomic_semop(sma, q);
/* Does q->sleeper still need to sleep? */
if (error > 0)
continue;
unlink_queue(sma, q);
if (error) {
restart = 0;
} else {
semop_completed = 1;
do_smart_wakeup_zero(sma, q->sops, q->nsops, wake_q);
restart = check_restart(sma, q);
}
wake_up_sem_queue_prepare(q, error, wake_q);
if (restart)
goto again;
}
return semop_completed;
}
/**
* set_semotime - set sem_otime
* @sma: semaphore array
* @sops: operations that modified the array, may be NULL
*
* sem_otime is replicated to avoid cache line trashing.
* This function sets one instance to the current time.
*/
static void set_semotime(struct sem_array *sma, struct sembuf *sops)
{
if (sops == NULL) {
sma->sems[0].sem_otime = get_seconds();
} else {
sma->sems[sops[0].sem_num].sem_otime =
get_seconds();
}
}
/**
* do_smart_update - optimized update_queue
* @sma: semaphore array
* @sops: operations that were performed
* @nsops: number of operations
* @otime: force setting otime
* @wake_q: lockless wake-queue head
*
* do_smart_update() does the required calls to update_queue and wakeup_zero,
* based on the actual changes that were performed on the semaphore array.
* Note that the function does not do the actual wake-up: the caller is
* responsible for calling wake_up_q().
* It is safe to perform this call after dropping all locks.
*/
static void do_smart_update(struct sem_array *sma, struct sembuf *sops, int nsops,
int otime, struct wake_q_head *wake_q)
{
int i;
otime |= do_smart_wakeup_zero(sma, sops, nsops, wake_q);
if (!list_empty(&sma->pending_alter)) {
/* semaphore array uses the global queue - just process it. */
otime |= update_queue(sma, -1, wake_q);
} else {
if (!sops) {
/*
* No sops, thus the modified semaphores are not
* known. Check all.
*/
for (i = 0; i < sma->sem_nsems; i++)
otime |= update_queue(sma, i, wake_q);
} else {
/*
* Check the semaphores that were increased:
* - No complex ops, thus all sleeping ops are
* decrease.
* - if we decreased the value, then any sleeping
* semaphore ops wont be able to run: If the
* previous value was too small, then the new
* value will be too small, too.
*/
for (i = 0; i < nsops; i++) {
if (sops[i].sem_op > 0) {
otime |= update_queue(sma,
sops[i].sem_num, wake_q);
}
}
}
}
if (otime)
set_semotime(sma, sops);
}
/*
* check_qop: Test if a queued operation sleeps on the semaphore semnum
*/
static int check_qop(struct sem_array *sma, int semnum, struct sem_queue *q,
bool count_zero)
{
struct sembuf *sop = q->blocking;
/*
* Linux always (since 0.99.10) reported a task as sleeping on all
* semaphores. This violates SUS, therefore it was changed to the
* standard compliant behavior.
* Give the administrators a chance to notice that an application
* might misbehave because it relies on the Linux behavior.
*/
pr_info_once("semctl(GETNCNT/GETZCNT) is since 3.16 Single Unix Specification compliant.\n"
"The task %s (%d) triggered the difference, watch for misbehavior.\n",
current->comm, task_pid_nr(current));
if (sop->sem_num != semnum)
return 0;
if (count_zero && sop->sem_op == 0)
return 1;
if (!count_zero && sop->sem_op < 0)
return 1;
return 0;
}
/* The following counts are associated to each semaphore:
* semncnt number of tasks waiting on semval being nonzero
* semzcnt number of tasks waiting on semval being zero
*
* Per definition, a task waits only on the semaphore of the first semop
* that cannot proceed, even if additional operation would block, too.
*/
static int count_semcnt(struct sem_array *sma, ushort semnum,
bool count_zero)
{
struct list_head *l;
struct sem_queue *q;
int semcnt;
semcnt = 0;
/* First: check the simple operations. They are easy to evaluate */
if (count_zero)
l = &sma->sems[semnum].pending_const;
else
l = &sma->sems[semnum].pending_alter;
list_for_each_entry(q, l, list) {
/* all task on a per-semaphore list sleep on exactly
* that semaphore
*/
semcnt++;
}
/* Then: check the complex operations. */
list_for_each_entry(q, &sma->pending_alter, list) {
semcnt += check_qop(sma, semnum, q, count_zero);
}
if (count_zero) {
list_for_each_entry(q, &sma->pending_const, list) {
semcnt += check_qop(sma, semnum, q, count_zero);
}
}
return semcnt;
}
/* Free a semaphore set. freeary() is called with sem_ids.rwsem locked
* as a writer and the spinlock for this semaphore set hold. sem_ids.rwsem
* remains locked on exit.
*/
static void freeary(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp)
{
struct sem_undo *un, *tu;
struct sem_queue *q, *tq;
struct sem_array *sma = container_of(ipcp, struct sem_array, sem_perm);
int i;
DEFINE_WAKE_Q(wake_q);
/* Free the existing undo structures for this semaphore set. */
ipc_assert_locked_object(&sma->sem_perm);
list_for_each_entry_safe(un, tu, &sma->list_id, list_id) {
list_del(&un->list_id);
spin_lock(&un->ulp->lock);
un->semid = -1;
list_del_rcu(&un->list_proc);
spin_unlock(&un->ulp->lock);
kfree_rcu(un, rcu);
}
/* Wake up all pending processes and let them fail with EIDRM. */
list_for_each_entry_safe(q, tq, &sma->pending_const, list) {
unlink_queue(sma, q);
wake_up_sem_queue_prepare(q, -EIDRM, &wake_q);
}
list_for_each_entry_safe(q, tq, &sma->pending_alter, list) {
unlink_queue(sma, q);
wake_up_sem_queue_prepare(q, -EIDRM, &wake_q);
}
for (i = 0; i < sma->sem_nsems; i++) {
struct sem *sem = &sma->sems[i];
list_for_each_entry_safe(q, tq, &sem->pending_const, list) {
unlink_queue(sma, q);
wake_up_sem_queue_prepare(q, -EIDRM, &wake_q);
}
list_for_each_entry_safe(q, tq, &sem->pending_alter, list) {
unlink_queue(sma, q);
wake_up_sem_queue_prepare(q, -EIDRM, &wake_q);
}
ipc_update_pid(&sem->sempid, NULL);
}
/* Remove the semaphore set from the IDR */
sem_rmid(ns, sma);
sem_unlock(sma, -1);
rcu_read_unlock();
wake_up_q(&wake_q);
ns->used_sems -= sma->sem_nsems;
ipc_rcu_putref(&sma->sem_perm, sem_rcu_free);
}
static unsigned long copy_semid_to_user(void __user *buf, struct semid64_ds *in, int version)
{
switch (version) {
case IPC_64:
return copy_to_user(buf, in, sizeof(*in));
case IPC_OLD:
{
struct semid_ds out;
memset(&out, 0, sizeof(out));
ipc64_perm_to_ipc_perm(&in->sem_perm, &out.sem_perm);
out.sem_otime = in->sem_otime;
out.sem_ctime = in->sem_ctime;
out.sem_nsems = in->sem_nsems;
return copy_to_user(buf, &out, sizeof(out));
}
default:
return -EINVAL;
}
}
static time64_t get_semotime(struct sem_array *sma)
{
int i;
time64_t res;
res = sma->sems[0].sem_otime;
for (i = 1; i < sma->sem_nsems; i++) {
time64_t to = sma->sems[i].sem_otime;
if (to > res)
res = to;
}
return res;
}
static int semctl_stat(struct ipc_namespace *ns, int semid,
int cmd, struct semid64_ds *semid64)
{
struct sem_array *sma;
int id = 0;
int err;
memset(semid64, 0, sizeof(*semid64));
rcu_read_lock();
if (cmd == SEM_STAT) {
sma = sem_obtain_object(ns, semid);
if (IS_ERR(sma)) {
err = PTR_ERR(sma);
goto out_unlock;
}
id = sma->sem_perm.id;
} else {
sma = sem_obtain_object_check(ns, semid);
if (IS_ERR(sma)) {
err = PTR_ERR(sma);
goto out_unlock;
}
}
err = -EACCES;
if (ipcperms(ns, &sma->sem_perm, S_IRUGO))
goto out_unlock;
err = security_sem_semctl(&sma->sem_perm, cmd);
if (err)
goto out_unlock;
ipc_lock_object(&sma->sem_perm);
if (!ipc_valid_object(&sma->sem_perm)) {
ipc_unlock_object(&sma->sem_perm);
err = -EIDRM;
goto out_unlock;
}
kernel_to_ipc64_perm(&sma->sem_perm, &semid64->sem_perm);
semid64->sem_otime = get_semotime(sma);
semid64->sem_ctime = sma->sem_ctime;
semid64->sem_nsems = sma->sem_nsems;
ipc_unlock_object(&sma->sem_perm);
rcu_read_unlock();
return id;
out_unlock:
rcu_read_unlock();
return err;
}
static int semctl_info(struct ipc_namespace *ns, int semid,
int cmd, void __user *p)
{
struct seminfo seminfo;
int max_id;
int err;
err = security_sem_semctl(NULL, cmd);
if (err)
return err;
memset(&seminfo, 0, sizeof(seminfo));
seminfo.semmni = ns->sc_semmni;
seminfo.semmns = ns->sc_semmns;
seminfo.semmsl = ns->sc_semmsl;
seminfo.semopm = ns->sc_semopm;
seminfo.semvmx = SEMVMX;
seminfo.semmnu = SEMMNU;
seminfo.semmap = SEMMAP;
seminfo.semume = SEMUME;
down_read(&sem_ids(ns).rwsem);
if (cmd == SEM_INFO) {
seminfo.semusz = sem_ids(ns).in_use;
seminfo.semaem = ns->used_sems;
} else {
seminfo.semusz = SEMUSZ;
seminfo.semaem = SEMAEM;
}
max_id = ipc_get_maxid(&sem_ids(ns));
up_read(&sem_ids(ns).rwsem);
if (copy_to_user(p, &seminfo, sizeof(struct seminfo)))
return -EFAULT;
return (max_id < 0) ? 0 : max_id;
}
static int semctl_setval(struct ipc_namespace *ns, int semid, int semnum,
int val)
{
struct sem_undo *un;
struct sem_array *sma;
struct sem *curr;
int err;
DEFINE_WAKE_Q(wake_q);
if (val > SEMVMX || val < 0)
return -ERANGE;
rcu_read_lock();
sma = sem_obtain_object_check(ns, semid);
if (IS_ERR(sma)) {
rcu_read_unlock();
return PTR_ERR(sma);
}
if (semnum < 0 || semnum >= sma->sem_nsems) {
rcu_read_unlock();
return -EINVAL;
}
if (ipcperms(ns, &sma->sem_perm, S_IWUGO)) {
rcu_read_unlock();
return -EACCES;
}
err = security_sem_semctl(&sma->sem_perm, SETVAL);
if (err) {
rcu_read_unlock();
return -EACCES;
}
sem_lock(sma, NULL, -1);
if (!ipc_valid_object(&sma->sem_perm)) {
sem_unlock(sma, -1);
rcu_read_unlock();
return -EIDRM;
}
curr = &sma->sems[semnum];
ipc_assert_locked_object(&sma->sem_perm);
list_for_each_entry(un, &sma->list_id, list_id)
un->semadj[semnum] = 0;
curr->semval = val;
ipc_update_pid(&curr->sempid, task_tgid(current));
sma->sem_ctime = ktime_get_real_seconds();
/* maybe some queued-up processes were waiting for this */
do_smart_update(sma, NULL, 0, 0, &wake_q);
sem_unlock(sma, -1);
rcu_read_unlock();
wake_up_q(&wake_q);
return 0;
}
static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
int cmd, void __user *p)
{
struct sem_array *sma;
struct sem *curr;
int err, nsems;
ushort fast_sem_io[SEMMSL_FAST];
ushort *sem_io = fast_sem_io;
DEFINE_WAKE_Q(wake_q);
rcu_read_lock();
sma = sem_obtain_object_check(ns, semid);
if (IS_ERR(sma)) {
rcu_read_unlock();
return PTR_ERR(sma);
}
nsems = sma->sem_nsems;
err = -EACCES;
if (ipcperms(ns, &sma->sem_perm, cmd == SETALL ? S_IWUGO : S_IRUGO))
goto out_rcu_wakeup;
err = security_sem_semctl(&sma->sem_perm, cmd);
if (err)
goto out_rcu_wakeup;
err = -EACCES;
switch (cmd) {
case GETALL:
{
ushort __user *array = p;
int i;
sem_lock(sma, NULL, -1);
if (!ipc_valid_object(&sma->sem_perm)) {
err = -EIDRM;
goto out_unlock;
}
if (nsems > SEMMSL_FAST) {
if (!ipc_rcu_getref(&sma->sem_perm)) {
err = -EIDRM;
goto out_unlock;
}
sem_unlock(sma, -1);
rcu_read_unlock();
sem_io = kvmalloc_array(nsems, sizeof(ushort),
GFP_KERNEL);
if (sem_io == NULL) {
ipc_rcu_putref(&sma->sem_perm, sem_rcu_free);
return -ENOMEM;
}
rcu_read_lock();
sem_lock_and_putref(sma);
if (!ipc_valid_object(&sma->sem_perm)) {
err = -EIDRM;
goto out_unlock;
}
}
for (i = 0; i < sma->sem_nsems; i++)
sem_io[i] = sma->sems[i].semval;
sem_unlock(sma, -1);
rcu_read_unlock();
err = 0;
if (copy_to_user(array, sem_io, nsems*sizeof(ushort)))
err = -EFAULT;
goto out_free;
}
case SETALL:
{
int i;
struct sem_undo *un;
if (!ipc_rcu_getref(&sma->sem_perm)) {
err = -EIDRM;
goto out_rcu_wakeup;
}
rcu_read_unlock();
if (nsems > SEMMSL_FAST) {
sem_io = kvmalloc_array(nsems, sizeof(ushort),
GFP_KERNEL);
if (sem_io == NULL) {
ipc_rcu_putref(&sma->sem_perm, sem_rcu_free);
return -ENOMEM;
}
}
if (copy_from_user(sem_io, p, nsems*sizeof(ushort))) {
ipc_rcu_putref(&sma->sem_perm, sem_rcu_free);
err = -EFAULT;
goto out_free;
}
for (i = 0; i < nsems; i++) {
if (sem_io[i] > SEMVMX) {
ipc_rcu_putref(&sma->sem_perm, sem_rcu_free);
err = -ERANGE;
goto out_free;
}
}
rcu_read_lock();
sem_lock_and_putref(sma);
if (!ipc_valid_object(&sma->sem_perm)) {
err = -EIDRM;
goto out_unlock;
}
for (i = 0; i < nsems; i++) {
sma->sems[i].semval = sem_io[i];
ipc_update_pid(&sma->sems[i].sempid, task_tgid(current));
}
ipc_assert_locked_object(&sma->sem_perm);
list_for_each_entry(un, &sma->list_id, list_id) {
for (i = 0; i < nsems; i++)
un->semadj[i] = 0;
}
sma->sem_ctime = ktime_get_real_seconds();
/* maybe some queued-up processes were waiting for this */
do_smart_update(sma, NULL, 0, 0, &wake_q);
err = 0;
goto out_unlock;
}
/* GETVAL, GETPID, GETNCTN, GETZCNT: fall-through */
}
err = -EINVAL;
if (semnum < 0 || semnum >= nsems)
goto out_rcu_wakeup;
sem_lock(sma, NULL, -1);
if (!ipc_valid_object(&sma->sem_perm)) {
err = -EIDRM;
goto out_unlock;
}
curr = &sma->sems[semnum];
switch (cmd) {
case GETVAL:
err = curr->semval;
goto out_unlock;
case GETPID:
err = pid_vnr(curr->sempid);
goto out_unlock;
case GETNCNT:
err = count_semcnt(sma, semnum, 0);
goto out_unlock;
case GETZCNT:
err = count_semcnt(sma, semnum, 1);
goto out_unlock;
}
out_unlock:
sem_unlock(sma, -1);
out_rcu_wakeup:
rcu_read_unlock();
wake_up_q(&wake_q);
out_free:
if (sem_io != fast_sem_io)
kvfree(sem_io);
return err;
}
static inline unsigned long
copy_semid_from_user(struct semid64_ds *out, void __user *buf, int version)
{
switch (version) {
case IPC_64:
if (copy_from_user(out, buf, sizeof(*out)))
return -EFAULT;
return 0;
case IPC_OLD:
{
struct semid_ds tbuf_old;
if (copy_from_user(&tbuf_old, buf, sizeof(tbuf_old)))
return -EFAULT;
out->sem_perm.uid = tbuf_old.sem_perm.uid;
out->sem_perm.gid = tbuf_old.sem_perm.gid;
out->sem_perm.mode = tbuf_old.sem_perm.mode;
return 0;
}
default:
return -EINVAL;
}
}
/*
* This function handles some semctl commands which require the rwsem
* to be held in write mode.
* NOTE: no locks must be held, the rwsem is taken inside this function.
*/
static int semctl_down(struct ipc_namespace *ns, int semid,
int cmd, struct semid64_ds *semid64)
{
struct sem_array *sma;
int err;
struct kern_ipc_perm *ipcp;
down_write(&sem_ids(ns).rwsem);
rcu_read_lock();
ipcp = ipcctl_pre_down_nolock(ns, &sem_ids(ns), semid, cmd,
&semid64->sem_perm, 0);
if (IS_ERR(ipcp)) {
err = PTR_ERR(ipcp);
goto out_unlock1;
}
sma = container_of(ipcp, struct sem_array, sem_perm);
err = security_sem_semctl(&sma->sem_perm, cmd);
if (err)
goto out_unlock1;
switch (cmd) {
case IPC_RMID:
sem_lock(sma, NULL, -1);
/* freeary unlocks the ipc object and rcu */
freeary(ns, ipcp);
goto out_up;
case IPC_SET:
sem_lock(sma, NULL, -1);
err = ipc_update_perm(&semid64->sem_perm, ipcp);
if (err)
goto out_unlock0;
sma->sem_ctime = ktime_get_real_seconds();
break;
default:
err = -EINVAL;
goto out_unlock1;
}
out_unlock0:
sem_unlock(sma, -1);
out_unlock1:
rcu_read_unlock();
out_up:
up_write(&sem_ids(ns).rwsem);
return err;
}
SYSCALL_DEFINE4(semctl, int, semid, int, semnum, int, cmd, unsigned long, arg)
{
int version;
struct ipc_namespace *ns;
void __user *p = (void __user *)arg;
struct semid64_ds semid64;
int err;
if (semid < 0)
return -EINVAL;
version = ipc_parse_version(&cmd);
ns = current->nsproxy->ipc_ns;
switch (cmd) {
case IPC_INFO:
case SEM_INFO:
return semctl_info(ns, semid, cmd, p);
case IPC_STAT:
case SEM_STAT:
err = semctl_stat(ns, semid, cmd, &semid64);
if (err < 0)
return err;
if (copy_semid_to_user(p, &semid64, version))
err = -EFAULT;
return err;
case GETALL:
case GETVAL:
case GETPID:
case GETNCNT:
case GETZCNT:
case SETALL:
return semctl_main(ns, semid, semnum, cmd, p);
case SETVAL: {
int val;
#if defined(CONFIG_64BIT) && defined(__BIG_ENDIAN)
/* big-endian 64bit */
val = arg >> 32;
#else
/* 32bit or little-endian 64bit */
val = arg;
#endif
return semctl_setval(ns, semid, semnum, val);
}
case IPC_SET:
if (copy_semid_from_user(&semid64, p, version))
return -EFAULT;
case IPC_RMID:
return semctl_down(ns, semid, cmd, &semid64);
default:
return -EINVAL;
}
}
#ifdef CONFIG_COMPAT
struct compat_semid_ds {
struct compat_ipc_perm sem_perm;
compat_time_t sem_otime;
compat_time_t sem_ctime;
compat_uptr_t sem_base;
compat_uptr_t sem_pending;
compat_uptr_t sem_pending_last;
compat_uptr_t undo;
unsigned short sem_nsems;
};
static int copy_compat_semid_from_user(struct semid64_ds *out, void __user *buf,
int version)
{
memset(out, 0, sizeof(*out));
if (version == IPC_64) {
struct compat_semid64_ds __user *p = buf;
return get_compat_ipc64_perm(&out->sem_perm, &p->sem_perm);
} else {
struct compat_semid_ds __user *p = buf;
return get_compat_ipc_perm(&out->sem_perm, &p->sem_perm);
}
}
static int copy_compat_semid_to_user(void __user *buf, struct semid64_ds *in,
int version)
{
if (version == IPC_64) {
struct compat_semid64_ds v;
memset(&v, 0, sizeof(v));
to_compat_ipc64_perm(&v.sem_perm, &in->sem_perm);
v.sem_otime = in->sem_otime;
v.sem_ctime = in->sem_ctime;
v.sem_nsems = in->sem_nsems;
return copy_to_user(buf, &v, sizeof(v));
} else {
struct compat_semid_ds v;
memset(&v, 0, sizeof(v));
to_compat_ipc_perm(&v.sem_perm, &in->sem_perm);
v.sem_otime = in->sem_otime;
v.sem_ctime = in->sem_ctime;
v.sem_nsems = in->sem_nsems;
return copy_to_user(buf, &v, sizeof(v));
}
}
COMPAT_SYSCALL_DEFINE4(semctl, int, semid, int, semnum, int, cmd, int, arg)
{
void __user *p = compat_ptr(arg);
struct ipc_namespace *ns;
struct semid64_ds semid64;
int version = compat_ipc_parse_version(&cmd);
int err;
ns = current->nsproxy->ipc_ns;
if (semid < 0)
return -EINVAL;
switch (cmd & (~IPC_64)) {
case IPC_INFO:
case SEM_INFO:
return semctl_info(ns, semid, cmd, p);
case IPC_STAT:
case SEM_STAT:
err = semctl_stat(ns, semid, cmd, &semid64);
if (err < 0)
return err;
if (copy_compat_semid_to_user(p, &semid64, version))
err = -EFAULT;
return err;
case GETVAL:
case GETPID:
case GETNCNT:
case GETZCNT:
case GETALL:
case SETALL:
return semctl_main(ns, semid, semnum, cmd, p);
case SETVAL:
return semctl_setval(ns, semid, semnum, arg);
case IPC_SET:
if (copy_compat_semid_from_user(&semid64, p, version))
return -EFAULT;
/* fallthru */
case IPC_RMID:
return semctl_down(ns, semid, cmd, &semid64);
default:
return -EINVAL;
}
}
#endif
/* If the task doesn't already have a undo_list, then allocate one
* here. We guarantee there is only one thread using this undo list,
* and current is THE ONE
*
* If this allocation and assignment succeeds, but later
* portions of this code fail, there is no need to free the sem_undo_list.
* Just let it stay associated with the task, and it'll be freed later
* at exit time.
*
* This can block, so callers must hold no locks.
*/
static inline int get_undo_list(struct sem_undo_list **undo_listp)
{
struct sem_undo_list *undo_list;
undo_list = current->sysvsem.undo_list;
if (!undo_list) {
undo_list = kzalloc(sizeof(*undo_list), GFP_KERNEL);
if (undo_list == NULL)
return -ENOMEM;
spin_lock_init(&undo_list->lock);
refcount_set(&undo_list->refcnt, 1);
INIT_LIST_HEAD(&undo_list->list_proc);
current->sysvsem.undo_list = undo_list;
}
*undo_listp = undo_list;
return 0;
}
static struct sem_undo *__lookup_undo(struct sem_undo_list *ulp, int semid)
{
struct sem_undo *un;
list_for_each_entry_rcu(un, &ulp->list_proc, list_proc) {
if (un->semid == semid)
return un;
}
return NULL;
}
static struct sem_undo *lookup_undo(struct sem_undo_list *ulp, int semid)
{
struct sem_undo *un;
assert_spin_locked(&ulp->lock);
un = __lookup_undo(ulp, semid);
if (un) {
list_del_rcu(&un->list_proc);
list_add_rcu(&un->list_proc, &ulp->list_proc);
}
return un;
}
/**
* find_alloc_undo - lookup (and if not present create) undo array
* @ns: namespace
* @semid: semaphore array id
*
* The function looks up (and if not present creates) the undo structure.
* The size of the undo structure depends on the size of the semaphore
* array, thus the alloc path is not that straightforward.
* Lifetime-rules: sem_undo is rcu-protected, on success, the function
* performs a rcu_read_lock().
*/
static struct sem_undo *find_alloc_undo(struct ipc_namespace *ns, int semid)
{
struct sem_array *sma;
struct sem_undo_list *ulp;
struct sem_undo *un, *new;
int nsems, error;
error = get_undo_list(&ulp);
if (error)
return ERR_PTR(error);
rcu_read_lock();
spin_lock(&ulp->lock);
un = lookup_undo(ulp, semid);
spin_unlock(&ulp->lock);
if (likely(un != NULL))
goto out;
/* no undo structure around - allocate one. */
/* step 1: figure out the size of the semaphore array */
sma = sem_obtain_object_check(ns, semid);
if (IS_ERR(sma)) {
rcu_read_unlock();
return ERR_CAST(sma);
}
nsems = sma->sem_nsems;
if (!ipc_rcu_getref(&sma->sem_perm)) {
rcu_read_unlock();
un = ERR_PTR(-EIDRM);
goto out;
}
rcu_read_unlock();
/* step 2: allocate new undo structure */
new = kzalloc(sizeof(struct sem_undo) + sizeof(short)*nsems, GFP_KERNEL);
if (!new) {
ipc_rcu_putref(&sma->sem_perm, sem_rcu_free);
return ERR_PTR(-ENOMEM);
}
/* step 3: Acquire the lock on semaphore array */
rcu_read_lock();
sem_lock_and_putref(sma);
if (!ipc_valid_object(&sma->sem_perm)) {
sem_unlock(sma, -1);
rcu_read_unlock();
kfree(new);
un = ERR_PTR(-EIDRM);
goto out;
}
spin_lock(&ulp->lock);
/*
* step 4: check for races: did someone else allocate the undo struct?
*/
un = lookup_undo(ulp, semid);
if (un) {
kfree(new);
goto success;
}
/* step 5: initialize & link new undo structure */
new->semadj = (short *) &new[1];
new->ulp = ulp;
new->semid = semid;
assert_spin_locked(&ulp->lock);
list_add_rcu(&new->list_proc, &ulp->list_proc);
ipc_assert_locked_object(&sma->sem_perm);
list_add(&new->list_id, &sma->list_id);
un = new;
success:
spin_unlock(&ulp->lock);
sem_unlock(sma, -1);
out:
return un;
}
static long do_semtimedop(int semid, struct sembuf __user *tsops,
unsigned nsops, const struct timespec64 *timeout)
{
int error = -EINVAL;
struct sem_array *sma;
struct sembuf fast_sops[SEMOPM_FAST];
struct sembuf *sops = fast_sops, *sop;
struct sem_undo *un;
int max, locknum;
bool undos = false, alter = false, dupsop = false;
struct sem_queue queue;
unsigned long dup = 0, jiffies_left = 0;
struct ipc_namespace *ns;
ns = current->nsproxy->ipc_ns;
if (nsops < 1 || semid < 0)
return -EINVAL;
if (nsops > ns->sc_semopm)
return -E2BIG;
if (nsops > SEMOPM_FAST) {
sops = kvmalloc(sizeof(*sops)*nsops, GFP_KERNEL);
if (sops == NULL)
return -ENOMEM;
}
if (copy_from_user(sops, tsops, nsops * sizeof(*tsops))) {
error = -EFAULT;
goto out_free;
}
if (timeout) {
if (timeout->tv_sec < 0 || timeout->tv_nsec < 0 ||
timeout->tv_nsec >= 1000000000L) {
error = -EINVAL;
goto out_free;
}
jiffies_left = timespec64_to_jiffies(timeout);
}
max = 0;
for (sop = sops; sop < sops + nsops; sop++) {
unsigned long mask = 1ULL << ((sop->sem_num) % BITS_PER_LONG);
if (sop->sem_num >= max)
max = sop->sem_num;
if (sop->sem_flg & SEM_UNDO)
undos = true;
if (dup & mask) {
/*
* There was a previous alter access that appears
* to have accessed the same semaphore, thus use
* the dupsop logic. "appears", because the detection
* can only check % BITS_PER_LONG.
*/
dupsop = true;
}
if (sop->sem_op != 0) {
alter = true;
dup |= mask;
}
}
if (undos) {
/* On success, find_alloc_undo takes the rcu_read_lock */
un = find_alloc_undo(ns, semid);
if (IS_ERR(un)) {
error = PTR_ERR(un);
goto out_free;
}
} else {
un = NULL;
rcu_read_lock();
}
sma = sem_obtain_object_check(ns, semid);
if (IS_ERR(sma)) {
rcu_read_unlock();
error = PTR_ERR(sma);
goto out_free;
}
error = -EFBIG;
if (max >= sma->sem_nsems) {
rcu_read_unlock();
goto out_free;
}
error = -EACCES;
if (ipcperms(ns, &sma->sem_perm, alter ? S_IWUGO : S_IRUGO)) {
rcu_read_unlock();
goto out_free;
}
error = security_sem_semop(&sma->sem_perm, sops, nsops, alter);
if (error) {
rcu_read_unlock();
goto out_free;
}
error = -EIDRM;
locknum = sem_lock(sma, sops, nsops);
/*
* We eventually might perform the following check in a lockless
* fashion, considering ipc_valid_object() locking constraints.
* If nsops == 1 and there is no contention for sem_perm.lock, then
* only a per-semaphore lock is held and it's OK to proceed with the
* check below. More details on the fine grained locking scheme
* entangled here and why it's RMID race safe on comments at sem_lock()
*/
if (!ipc_valid_object(&sma->sem_perm))
goto out_unlock_free;
/*
* semid identifiers are not unique - find_alloc_undo may have
* allocated an undo structure, it was invalidated by an RMID
* and now a new array with received the same id. Check and fail.
* This case can be detected checking un->semid. The existence of
* "un" itself is guaranteed by rcu.
*/
if (un && un->semid == -1)
goto out_unlock_free;
queue.sops = sops;
queue.nsops = nsops;
queue.undo = un;
queue.pid = task_tgid(current);
queue.alter = alter;
queue.dupsop = dupsop;
error = perform_atomic_semop(sma, &queue);
if (error == 0) { /* non-blocking succesfull path */
DEFINE_WAKE_Q(wake_q);
/*
* If the operation was successful, then do
* the required updates.
*/
if (alter)
do_smart_update(sma, sops, nsops, 1, &wake_q);
else
set_semotime(sma, sops);
sem_unlock(sma, locknum);
rcu_read_unlock();
wake_up_q(&wake_q);
goto out_free;
}
if (error < 0) /* non-blocking error path */
goto out_unlock_free;
/*
* We need to sleep on this operation, so we put the current
* task into the pending queue and go to sleep.
*/
if (nsops == 1) {
struct sem *curr;
curr = &sma->sems[sops->sem_num];
if (alter) {
if (sma->complex_count) {
list_add_tail(&queue.list,
&sma->pending_alter);
} else {
list_add_tail(&queue.list,
&curr->pending_alter);
}
} else {
list_add_tail(&queue.list, &curr->pending_const);
}
} else {
if (!sma->complex_count)
merge_queues(sma);
if (alter)
list_add_tail(&queue.list, &sma->pending_alter);
else
list_add_tail(&queue.list, &sma->pending_const);
sma->complex_count++;
}
do {
queue.status = -EINTR;
queue.sleeper = current;
__set_current_state(TASK_INTERRUPTIBLE);
sem_unlock(sma, locknum);
rcu_read_unlock();
if (timeout)
jiffies_left = schedule_timeout(jiffies_left);
else
schedule();
/*
* fastpath: the semop has completed, either successfully or
* not, from the syscall pov, is quite irrelevant to us at this
* point; we're done.
*
* We _do_ care, nonetheless, about being awoken by a signal or
* spuriously. The queue.status is checked again in the
* slowpath (aka after taking sem_lock), such that we can detect
* scenarios where we were awakened externally, during the
* window between wake_q_add() and wake_up_q().
*/
error = READ_ONCE(queue.status);
if (error != -EINTR) {
/*
* User space could assume that semop() is a memory
* barrier: Without the mb(), the cpu could
* speculatively read in userspace stale data that was
* overwritten by the previous owner of the semaphore.
*/
smp_mb();
goto out_free;
}
rcu_read_lock();
locknum = sem_lock(sma, sops, nsops);
if (!ipc_valid_object(&sma->sem_perm))
goto out_unlock_free;
error = READ_ONCE(queue.status);
/*
* If queue.status != -EINTR we are woken up by another process.
* Leave without unlink_queue(), but with sem_unlock().
*/
if (error != -EINTR)
goto out_unlock_free;
/*
* If an interrupt occurred we have to clean up the queue.
*/
if (timeout && jiffies_left == 0)
error = -EAGAIN;
} while (error == -EINTR && !signal_pending(current)); /* spurious */
unlink_queue(sma, &queue);
out_unlock_free:
sem_unlock(sma, locknum);
rcu_read_unlock();
out_free:
if (sops != fast_sops)
kvfree(sops);
return error;
}
SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
unsigned, nsops, const struct timespec __user *, timeout)
{
if (timeout) {
struct timespec64 ts;
if (get_timespec64(&ts, timeout))
return -EFAULT;
return do_semtimedop(semid, tsops, nsops, &ts);
}
return do_semtimedop(semid, tsops, nsops, NULL);
}
#ifdef CONFIG_COMPAT
COMPAT_SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsems,
unsigned, nsops,
const struct compat_timespec __user *, timeout)
{
if (timeout) {
struct timespec64 ts;
if (compat_get_timespec64(&ts, timeout))
return -EFAULT;
return do_semtimedop(semid, tsems, nsops, &ts);
}
return do_semtimedop(semid, tsems, nsops, NULL);
}
#endif
SYSCALL_DEFINE3(semop, int, semid, struct sembuf __user *, tsops,
unsigned, nsops)
{
return do_semtimedop(semid, tsops, nsops, NULL);
}
/* If CLONE_SYSVSEM is set, establish sharing of SEM_UNDO state between
* parent and child tasks.
*/
int copy_semundo(unsigned long clone_flags, struct task_struct *tsk)
{
struct sem_undo_list *undo_list;
int error;
if (clone_flags & CLONE_SYSVSEM) {
error = get_undo_list(&undo_list);
if (error)
return error;
refcount_inc(&undo_list->refcnt);
tsk->sysvsem.undo_list = undo_list;
} else
tsk->sysvsem.undo_list = NULL;
return 0;
}
/*
* add semadj values to semaphores, free undo structures.
* undo structures are not freed when semaphore arrays are destroyed
* so some of them may be out of date.
* IMPLEMENTATION NOTE: There is some confusion over whether the
* set of adjustments that needs to be done should be done in an atomic
* manner or not. That is, if we are attempting to decrement the semval
* should we queue up and wait until we can do so legally?
* The original implementation attempted to do this (queue and wait).
* The current implementation does not do so. The POSIX standard
* and SVID should be consulted to determine what behavior is mandated.
*/
void exit_sem(struct task_struct *tsk)
{
struct sem_undo_list *ulp;
ulp = tsk->sysvsem.undo_list;
if (!ulp)
return;
tsk->sysvsem.undo_list = NULL;
if (!refcount_dec_and_test(&ulp->refcnt))
return;
for (;;) {
struct sem_array *sma;
struct sem_undo *un;
int semid, i;
DEFINE_WAKE_Q(wake_q);
cond_resched();
rcu_read_lock();
un = list_entry_rcu(ulp->list_proc.next,
struct sem_undo, list_proc);
if (&un->list_proc == &ulp->list_proc) {
/*
* We must wait for freeary() before freeing this ulp,
* in case we raced with last sem_undo. There is a small
* possibility where we exit while freeary() didn't
* finish unlocking sem_undo_list.
*/
spin_lock(&ulp->lock);
spin_unlock(&ulp->lock);
rcu_read_unlock();
break;
}
spin_lock(&ulp->lock);
semid = un->semid;
spin_unlock(&ulp->lock);
/* exit_sem raced with IPC_RMID, nothing to do */
if (semid == -1) {
rcu_read_unlock();
continue;
}
sma = sem_obtain_object_check(tsk->nsproxy->ipc_ns, semid);
/* exit_sem raced with IPC_RMID, nothing to do */
if (IS_ERR(sma)) {
rcu_read_unlock();
continue;
}
sem_lock(sma, NULL, -1);
/* exit_sem raced with IPC_RMID, nothing to do */
if (!ipc_valid_object(&sma->sem_perm)) {
sem_unlock(sma, -1);
rcu_read_unlock();
continue;
}
un = __lookup_undo(ulp, semid);
if (un == NULL) {
/* exit_sem raced with IPC_RMID+semget() that created
* exactly the same semid. Nothing to do.
*/
sem_unlock(sma, -1);
rcu_read_unlock();
continue;
}
/* remove un from the linked lists */
ipc_assert_locked_object(&sma->sem_perm);
list_del(&un->list_id);
/* we are the last process using this ulp, acquiring ulp->lock
* isn't required. Besides that, we are also protected against
* IPC_RMID as we hold sma->sem_perm lock now
*/
list_del_rcu(&un->list_proc);
/* perform adjustments registered in un */
for (i = 0; i < sma->sem_nsems; i++) {
struct sem *semaphore = &sma->sems[i];
if (un->semadj[i]) {
semaphore->semval += un->semadj[i];
/*
* Range checks of the new semaphore value,
* not defined by sus:
* - Some unices ignore the undo entirely
* (e.g. HP UX 11i 11.22, Tru64 V5.1)
* - some cap the value (e.g. FreeBSD caps
* at 0, but doesn't enforce SEMVMX)
*
* Linux caps the semaphore value, both at 0
* and at SEMVMX.
*
* Manfred <manfred@colorfullife.com>
*/
if (semaphore->semval < 0)
semaphore->semval = 0;
if (semaphore->semval > SEMVMX)
semaphore->semval = SEMVMX;
ipc_update_pid(&semaphore->sempid, task_tgid(current));
}
}
/* maybe some queued-up processes were waiting for this */
do_smart_update(sma, NULL, 0, 1, &wake_q);
sem_unlock(sma, -1);
rcu_read_unlock();
wake_up_q(&wake_q);
kfree_rcu(un, rcu);
}
kfree(ulp);
}
#ifdef CONFIG_PROC_FS
static int sysvipc_sem_proc_show(struct seq_file *s, void *it)
{
struct user_namespace *user_ns = seq_user_ns(s);
struct kern_ipc_perm *ipcp = it;
struct sem_array *sma = container_of(ipcp, struct sem_array, sem_perm);
time64_t sem_otime;
/*
* The proc interface isn't aware of sem_lock(), it calls
* ipc_lock_object() directly (in sysvipc_find_ipc).
* In order to stay compatible with sem_lock(), we must
* enter / leave complex_mode.
*/
complexmode_enter(sma);
sem_otime = get_semotime(sma);
seq_printf(s,
"%10d %10d %4o %10u %5u %5u %5u %5u %10llu %10llu\n",
sma->sem_perm.key,
sma->sem_perm.id,
sma->sem_perm.mode,
sma->sem_nsems,
from_kuid_munged(user_ns, sma->sem_perm.uid),
from_kgid_munged(user_ns, sma->sem_perm.gid),
from_kuid_munged(user_ns, sma->sem_perm.cuid),
from_kgid_munged(user_ns, sma->sem_perm.cgid),
sem_otime,
sma->sem_ctime);
complexmode_tryleave(sma);
return 0;
}
#endif