linux/security/keys/process_keys.c
Andy Lutomirski 58319057b7 capabilities: ambient capabilities
Credit where credit is due: this idea comes from Christoph Lameter with
a lot of valuable input from Serge Hallyn.  This patch is heavily based
on Christoph's patch.

===== The status quo =====

On Linux, there are a number of capabilities defined by the kernel.  To
perform various privileged tasks, processes can wield capabilities that
they hold.

Each task has four capability masks: effective (pE), permitted (pP),
inheritable (pI), and a bounding set (X).  When the kernel checks for a
capability, it checks pE.  The other capability masks serve to modify
what capabilities can be in pE.

Any task can remove capabilities from pE, pP, or pI at any time.  If a
task has a capability in pP, it can add that capability to pE and/or pI.
If a task has CAP_SETPCAP, then it can add any capability to pI, and it
can remove capabilities from X.

Tasks are not the only things that can have capabilities; files can also
have capabilities.  A file can have no capabilty information at all [1].
If a file has capability information, then it has a permitted mask (fP)
and an inheritable mask (fI) as well as a single effective bit (fE) [2].
File capabilities modify the capabilities of tasks that execve(2) them.

A task that successfully calls execve has its capabilities modified for
the file ultimately being excecuted (i.e.  the binary itself if that
binary is ELF or for the interpreter if the binary is a script.) [3] In
the capability evolution rules, for each mask Z, pZ represents the old
value and pZ' represents the new value.  The rules are:

  pP' = (X & fP) | (pI & fI)
  pI' = pI
  pE' = (fE ? pP' : 0)
  X is unchanged

For setuid binaries, fP, fI, and fE are modified by a moderately
complicated set of rules that emulate POSIX behavior.  Similarly, if
euid == 0 or ruid == 0, then fP, fI, and fE are modified differently
(primary, fP and fI usually end up being the full set).  For nonroot
users executing binaries with neither setuid nor file caps, fI and fP
are empty and fE is false.

As an extra complication, if you execute a process as nonroot and fE is
set, then the "secure exec" rules are in effect: AT_SECURE gets set,
LD_PRELOAD doesn't work, etc.

This is rather messy.  We've learned that making any changes is
dangerous, though: if a new kernel version allows an unprivileged
program to change its security state in a way that persists cross
execution of a setuid program or a program with file caps, this
persistent state is surprisingly likely to allow setuid or file-capped
programs to be exploited for privilege escalation.

===== The problem =====

Capability inheritance is basically useless.

If you aren't root and you execute an ordinary binary, fI is zero, so
your capabilities have no effect whatsoever on pP'.  This means that you
can't usefully execute a helper process or a shell command with elevated
capabilities if you aren't root.

On current kernels, you can sort of work around this by setting fI to
the full set for most or all non-setuid executable files.  This causes
pP' = pI for nonroot, and inheritance works.  No one does this because
it's a PITA and it isn't even supported on most filesystems.

If you try this, you'll discover that every nonroot program ends up with
secure exec rules, breaking many things.

This is a problem that has bitten many people who have tried to use
capabilities for anything useful.

===== The proposed change =====

This patch adds a fifth capability mask called the ambient mask (pA).
pA does what most people expect pI to do.

pA obeys the invariant that no bit can ever be set in pA if it is not
set in both pP and pI.  Dropping a bit from pP or pI drops that bit from
pA.  This ensures that existing programs that try to drop capabilities
still do so, with a complication.  Because capability inheritance is so
broken, setting KEEPCAPS, using setresuid to switch to nonroot uids, and
then calling execve effectively drops capabilities.  Therefore,
setresuid from root to nonroot conditionally clears pA unless
SECBIT_NO_SETUID_FIXUP is set.  Processes that don't like this can
re-add bits to pA afterwards.

The capability evolution rules are changed:

  pA' = (file caps or setuid or setgid ? 0 : pA)
  pP' = (X & fP) | (pI & fI) | pA'
  pI' = pI
  pE' = (fE ? pP' : pA')
  X is unchanged

If you are nonroot but you have a capability, you can add it to pA.  If
you do so, your children get that capability in pA, pP, and pE.  For
example, you can set pA = CAP_NET_BIND_SERVICE, and your children can
automatically bind low-numbered ports.  Hallelujah!

Unprivileged users can create user namespaces, map themselves to a
nonzero uid, and create both privileged (relative to their namespace)
and unprivileged process trees.  This is currently more or less
impossible.  Hallelujah!

You cannot use pA to try to subvert a setuid, setgid, or file-capped
program: if you execute any such program, pA gets cleared and the
resulting evolution rules are unchanged by this patch.

Users with nonzero pA are unlikely to unintentionally leak that
capability.  If they run programs that try to drop privileges, dropping
privileges will still work.

It's worth noting that the degree of paranoia in this patch could
possibly be reduced without causing serious problems.  Specifically, if
we allowed pA to persist across executing non-pA-aware setuid binaries
and across setresuid, then, naively, the only capabilities that could
leak as a result would be the capabilities in pA, and any attacker
*already* has those capabilities.  This would make me nervous, though --
setuid binaries that tried to privilege-separate might fail to do so,
and putting CAP_DAC_READ_SEARCH or CAP_DAC_OVERRIDE into pA could have
unexpected side effects.  (Whether these unexpected side effects would
be exploitable is an open question.) I've therefore taken the more
paranoid route.  We can revisit this later.

An alternative would be to require PR_SET_NO_NEW_PRIVS before setting
ambient capabilities.  I think that this would be annoying and would
make granting otherwise unprivileged users minor ambient capabilities
(CAP_NET_BIND_SERVICE or CAP_NET_RAW for example) much less useful than
it is with this patch.

===== Footnotes =====

[1] Files that are missing the "security.capability" xattr or that have
unrecognized values for that xattr end up with has_cap set to false.
The code that does that appears to be complicated for no good reason.

[2] The libcap capability mask parsers and formatters are dangerously
misleading and the documentation is flat-out wrong.  fE is *not* a mask;
it's a single bit.  This has probably confused every single person who
has tried to use file capabilities.

[3] Linux very confusingly processes both the script and the interpreter
if applicable, for reasons that elude me.  The results from thinking
about a script's file capabilities and/or setuid bits are mostly
discarded.

Preliminary userspace code is here, but it needs updating:
https://git.kernel.org/cgit/linux/kernel/git/luto/util-linux-playground.git/commit/?h=cap_ambient&id=7f5afbd175d2

Here is a test program that can be used to verify the functionality
(from Christoph):

/*
 * Test program for the ambient capabilities. This program spawns a shell
 * that allows running processes with a defined set of capabilities.
 *
 * (C) 2015 Christoph Lameter <cl@linux.com>
 * Released under: GPL v3 or later.
 *
 *
 * Compile using:
 *
 *	gcc -o ambient_test ambient_test.o -lcap-ng
 *
 * This program must have the following capabilities to run properly:
 * Permissions for CAP_NET_RAW, CAP_NET_ADMIN, CAP_SYS_NICE
 *
 * A command to equip the binary with the right caps is:
 *
 *	setcap cap_net_raw,cap_net_admin,cap_sys_nice+p ambient_test
 *
 *
 * To get a shell with additional caps that can be inherited by other processes:
 *
 *	./ambient_test /bin/bash
 *
 *
 * Verifying that it works:
 *
 * From the bash spawed by ambient_test run
 *
 *	cat /proc/$$/status
 *
 * and have a look at the capabilities.
 */

#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <cap-ng.h>
#include <sys/prctl.h>
#include <linux/capability.h>

/*
 * Definitions from the kernel header files. These are going to be removed
 * when the /usr/include files have these defined.
 */
#define PR_CAP_AMBIENT 47
#define PR_CAP_AMBIENT_IS_SET 1
#define PR_CAP_AMBIENT_RAISE 2
#define PR_CAP_AMBIENT_LOWER 3
#define PR_CAP_AMBIENT_CLEAR_ALL 4

static void set_ambient_cap(int cap)
{
	int rc;

	capng_get_caps_process();
	rc = capng_update(CAPNG_ADD, CAPNG_INHERITABLE, cap);
	if (rc) {
		printf("Cannot add inheritable cap\n");
		exit(2);
	}
	capng_apply(CAPNG_SELECT_CAPS);

	/* Note the two 0s at the end. Kernel checks for these */
	if (prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_RAISE, cap, 0, 0)) {
		perror("Cannot set cap");
		exit(1);
	}
}

int main(int argc, char **argv)
{
	int rc;

	set_ambient_cap(CAP_NET_RAW);
	set_ambient_cap(CAP_NET_ADMIN);
	set_ambient_cap(CAP_SYS_NICE);

	printf("Ambient_test forking shell\n");
	if (execv(argv[1], argv + 1))
		perror("Cannot exec");

	return 0;
}

Signed-off-by: Christoph Lameter <cl@linux.com> # Original author
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Aaron Jones <aaronmdjones@gmail.com>
Cc: Ted Ts'o <tytso@mit.edu>
Cc: Andrew G. Morgan <morgan@kernel.org>
Cc: Mimi Zohar <zohar@linux.vnet.ibm.com>
Cc: Austin S Hemmelgarn <ahferroin7@gmail.com>
Cc: Markku Savela <msa@moth.iki.fi>
Cc: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: James Morris <james.l.morris@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-09-04 16:54:41 -07:00

872 lines
20 KiB
C

/* Manage a process's keyrings
*
* Copyright (C) 2004-2005, 2008 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version
* 2 of the License, or (at your option) any later version.
*/
#include <linux/module.h>
#include <linux/init.h>
#include <linux/sched.h>
#include <linux/keyctl.h>
#include <linux/fs.h>
#include <linux/err.h>
#include <linux/mutex.h>
#include <linux/security.h>
#include <linux/user_namespace.h>
#include <asm/uaccess.h>
#include "internal.h"
/* Session keyring create vs join semaphore */
static DEFINE_MUTEX(key_session_mutex);
/* User keyring creation semaphore */
static DEFINE_MUTEX(key_user_keyring_mutex);
/* The root user's tracking struct */
struct key_user root_key_user = {
.usage = ATOMIC_INIT(3),
.cons_lock = __MUTEX_INITIALIZER(root_key_user.cons_lock),
.lock = __SPIN_LOCK_UNLOCKED(root_key_user.lock),
.nkeys = ATOMIC_INIT(2),
.nikeys = ATOMIC_INIT(2),
.uid = GLOBAL_ROOT_UID,
};
/*
* Install the user and user session keyrings for the current process's UID.
*/
int install_user_keyrings(void)
{
struct user_struct *user;
const struct cred *cred;
struct key *uid_keyring, *session_keyring;
key_perm_t user_keyring_perm;
char buf[20];
int ret;
uid_t uid;
user_keyring_perm = (KEY_POS_ALL & ~KEY_POS_SETATTR) | KEY_USR_ALL;
cred = current_cred();
user = cred->user;
uid = from_kuid(cred->user_ns, user->uid);
kenter("%p{%u}", user, uid);
if (user->uid_keyring && user->session_keyring) {
kleave(" = 0 [exist]");
return 0;
}
mutex_lock(&key_user_keyring_mutex);
ret = 0;
if (!user->uid_keyring) {
/* get the UID-specific keyring
* - there may be one in existence already as it may have been
* pinned by a session, but the user_struct pointing to it
* may have been destroyed by setuid */
sprintf(buf, "_uid.%u", uid);
uid_keyring = find_keyring_by_name(buf, true);
if (IS_ERR(uid_keyring)) {
uid_keyring = keyring_alloc(buf, user->uid, INVALID_GID,
cred, user_keyring_perm,
KEY_ALLOC_IN_QUOTA, NULL);
if (IS_ERR(uid_keyring)) {
ret = PTR_ERR(uid_keyring);
goto error;
}
}
/* get a default session keyring (which might also exist
* already) */
sprintf(buf, "_uid_ses.%u", uid);
session_keyring = find_keyring_by_name(buf, true);
if (IS_ERR(session_keyring)) {
session_keyring =
keyring_alloc(buf, user->uid, INVALID_GID,
cred, user_keyring_perm,
KEY_ALLOC_IN_QUOTA, NULL);
if (IS_ERR(session_keyring)) {
ret = PTR_ERR(session_keyring);
goto error_release;
}
/* we install a link from the user session keyring to
* the user keyring */
ret = key_link(session_keyring, uid_keyring);
if (ret < 0)
goto error_release_both;
}
/* install the keyrings */
user->uid_keyring = uid_keyring;
user->session_keyring = session_keyring;
}
mutex_unlock(&key_user_keyring_mutex);
kleave(" = 0");
return 0;
error_release_both:
key_put(session_keyring);
error_release:
key_put(uid_keyring);
error:
mutex_unlock(&key_user_keyring_mutex);
kleave(" = %d", ret);
return ret;
}
/*
* Install a fresh thread keyring directly to new credentials. This keyring is
* allowed to overrun the quota.
*/
int install_thread_keyring_to_cred(struct cred *new)
{
struct key *keyring;
keyring = keyring_alloc("_tid", new->uid, new->gid, new,
KEY_POS_ALL | KEY_USR_VIEW,
KEY_ALLOC_QUOTA_OVERRUN, NULL);
if (IS_ERR(keyring))
return PTR_ERR(keyring);
new->thread_keyring = keyring;
return 0;
}
/*
* Install a fresh thread keyring, discarding the old one.
*/
static int install_thread_keyring(void)
{
struct cred *new;
int ret;
new = prepare_creds();
if (!new)
return -ENOMEM;
BUG_ON(new->thread_keyring);
ret = install_thread_keyring_to_cred(new);
if (ret < 0) {
abort_creds(new);
return ret;
}
return commit_creds(new);
}
/*
* Install a process keyring directly to a credentials struct.
*
* Returns -EEXIST if there was already a process keyring, 0 if one installed,
* and other value on any other error
*/
int install_process_keyring_to_cred(struct cred *new)
{
struct key *keyring;
if (new->process_keyring)
return -EEXIST;
keyring = keyring_alloc("_pid", new->uid, new->gid, new,
KEY_POS_ALL | KEY_USR_VIEW,
KEY_ALLOC_QUOTA_OVERRUN, NULL);
if (IS_ERR(keyring))
return PTR_ERR(keyring);
new->process_keyring = keyring;
return 0;
}
/*
* Make sure a process keyring is installed for the current process. The
* existing process keyring is not replaced.
*
* Returns 0 if there is a process keyring by the end of this function, some
* error otherwise.
*/
static int install_process_keyring(void)
{
struct cred *new;
int ret;
new = prepare_creds();
if (!new)
return -ENOMEM;
ret = install_process_keyring_to_cred(new);
if (ret < 0) {
abort_creds(new);
return ret != -EEXIST ? ret : 0;
}
return commit_creds(new);
}
/*
* Install a session keyring directly to a credentials struct.
*/
int install_session_keyring_to_cred(struct cred *cred, struct key *keyring)
{
unsigned long flags;
struct key *old;
might_sleep();
/* create an empty session keyring */
if (!keyring) {
flags = KEY_ALLOC_QUOTA_OVERRUN;
if (cred->session_keyring)
flags = KEY_ALLOC_IN_QUOTA;
keyring = keyring_alloc("_ses", cred->uid, cred->gid, cred,
KEY_POS_ALL | KEY_USR_VIEW | KEY_USR_READ,
flags, NULL);
if (IS_ERR(keyring))
return PTR_ERR(keyring);
} else {
__key_get(keyring);
}
/* install the keyring */
old = cred->session_keyring;
rcu_assign_pointer(cred->session_keyring, keyring);
if (old)
key_put(old);
return 0;
}
/*
* Install a session keyring, discarding the old one. If a keyring is not
* supplied, an empty one is invented.
*/
static int install_session_keyring(struct key *keyring)
{
struct cred *new;
int ret;
new = prepare_creds();
if (!new)
return -ENOMEM;
ret = install_session_keyring_to_cred(new, keyring);
if (ret < 0) {
abort_creds(new);
return ret;
}
return commit_creds(new);
}
/*
* Handle the fsuid changing.
*/
void key_fsuid_changed(struct task_struct *tsk)
{
/* update the ownership of the thread keyring */
BUG_ON(!tsk->cred);
if (tsk->cred->thread_keyring) {
down_write(&tsk->cred->thread_keyring->sem);
tsk->cred->thread_keyring->uid = tsk->cred->fsuid;
up_write(&tsk->cred->thread_keyring->sem);
}
}
/*
* Handle the fsgid changing.
*/
void key_fsgid_changed(struct task_struct *tsk)
{
/* update the ownership of the thread keyring */
BUG_ON(!tsk->cred);
if (tsk->cred->thread_keyring) {
down_write(&tsk->cred->thread_keyring->sem);
tsk->cred->thread_keyring->gid = tsk->cred->fsgid;
up_write(&tsk->cred->thread_keyring->sem);
}
}
/*
* Search the process keyrings attached to the supplied cred for the first
* matching key.
*
* The search criteria are the type and the match function. The description is
* given to the match function as a parameter, but doesn't otherwise influence
* the search. Typically the match function will compare the description
* parameter to the key's description.
*
* This can only search keyrings that grant Search permission to the supplied
* credentials. Keyrings linked to searched keyrings will also be searched if
* they grant Search permission too. Keys can only be found if they grant
* Search permission to the credentials.
*
* Returns a pointer to the key with the key usage count incremented if
* successful, -EAGAIN if we didn't find any matching key or -ENOKEY if we only
* matched negative keys.
*
* In the case of a successful return, the possession attribute is set on the
* returned key reference.
*/
key_ref_t search_my_process_keyrings(struct keyring_search_context *ctx)
{
key_ref_t key_ref, ret, err;
/* we want to return -EAGAIN or -ENOKEY if any of the keyrings were
* searchable, but we failed to find a key or we found a negative key;
* otherwise we want to return a sample error (probably -EACCES) if
* none of the keyrings were searchable
*
* in terms of priority: success > -ENOKEY > -EAGAIN > other error
*/
key_ref = NULL;
ret = NULL;
err = ERR_PTR(-EAGAIN);
/* search the thread keyring first */
if (ctx->cred->thread_keyring) {
key_ref = keyring_search_aux(
make_key_ref(ctx->cred->thread_keyring, 1), ctx);
if (!IS_ERR(key_ref))
goto found;
switch (PTR_ERR(key_ref)) {
case -EAGAIN: /* no key */
case -ENOKEY: /* negative key */
ret = key_ref;
break;
default:
err = key_ref;
break;
}
}
/* search the process keyring second */
if (ctx->cred->process_keyring) {
key_ref = keyring_search_aux(
make_key_ref(ctx->cred->process_keyring, 1), ctx);
if (!IS_ERR(key_ref))
goto found;
switch (PTR_ERR(key_ref)) {
case -EAGAIN: /* no key */
if (ret)
break;
case -ENOKEY: /* negative key */
ret = key_ref;
break;
default:
err = key_ref;
break;
}
}
/* search the session keyring */
if (ctx->cred->session_keyring) {
rcu_read_lock();
key_ref = keyring_search_aux(
make_key_ref(rcu_dereference(ctx->cred->session_keyring), 1),
ctx);
rcu_read_unlock();
if (!IS_ERR(key_ref))
goto found;
switch (PTR_ERR(key_ref)) {
case -EAGAIN: /* no key */
if (ret)
break;
case -ENOKEY: /* negative key */
ret = key_ref;
break;
default:
err = key_ref;
break;
}
}
/* or search the user-session keyring */
else if (ctx->cred->user->session_keyring) {
key_ref = keyring_search_aux(
make_key_ref(ctx->cred->user->session_keyring, 1),
ctx);
if (!IS_ERR(key_ref))
goto found;
switch (PTR_ERR(key_ref)) {
case -EAGAIN: /* no key */
if (ret)
break;
case -ENOKEY: /* negative key */
ret = key_ref;
break;
default:
err = key_ref;
break;
}
}
/* no key - decide on the error we're going to go for */
key_ref = ret ? ret : err;
found:
return key_ref;
}
/*
* Search the process keyrings attached to the supplied cred for the first
* matching key in the manner of search_my_process_keyrings(), but also search
* the keys attached to the assumed authorisation key using its credentials if
* one is available.
*
* Return same as search_my_process_keyrings().
*/
key_ref_t search_process_keyrings(struct keyring_search_context *ctx)
{
struct request_key_auth *rka;
key_ref_t key_ref, ret = ERR_PTR(-EACCES), err;
might_sleep();
key_ref = search_my_process_keyrings(ctx);
if (!IS_ERR(key_ref))
goto found;
err = key_ref;
/* if this process has an instantiation authorisation key, then we also
* search the keyrings of the process mentioned there
* - we don't permit access to request_key auth keys via this method
*/
if (ctx->cred->request_key_auth &&
ctx->cred == current_cred() &&
ctx->index_key.type != &key_type_request_key_auth
) {
const struct cred *cred = ctx->cred;
/* defend against the auth key being revoked */
down_read(&cred->request_key_auth->sem);
if (key_validate(ctx->cred->request_key_auth) == 0) {
rka = ctx->cred->request_key_auth->payload.data;
ctx->cred = rka->cred;
key_ref = search_process_keyrings(ctx);
ctx->cred = cred;
up_read(&cred->request_key_auth->sem);
if (!IS_ERR(key_ref))
goto found;
ret = key_ref;
} else {
up_read(&cred->request_key_auth->sem);
}
}
/* no key - decide on the error we're going to go for */
if (err == ERR_PTR(-ENOKEY) || ret == ERR_PTR(-ENOKEY))
key_ref = ERR_PTR(-ENOKEY);
else if (err == ERR_PTR(-EACCES))
key_ref = ret;
else
key_ref = err;
found:
return key_ref;
}
/*
* See if the key we're looking at is the target key.
*/
bool lookup_user_key_possessed(const struct key *key,
const struct key_match_data *match_data)
{
return key == match_data->raw_data;
}
/*
* Look up a key ID given us by userspace with a given permissions mask to get
* the key it refers to.
*
* Flags can be passed to request that special keyrings be created if referred
* to directly, to permit partially constructed keys to be found and to skip
* validity and permission checks on the found key.
*
* Returns a pointer to the key with an incremented usage count if successful;
* -EINVAL if the key ID is invalid; -ENOKEY if the key ID does not correspond
* to a key or the best found key was a negative key; -EKEYREVOKED or
* -EKEYEXPIRED if the best found key was revoked or expired; -EACCES if the
* found key doesn't grant the requested permit or the LSM denied access to it;
* or -ENOMEM if a special keyring couldn't be created.
*
* In the case of a successful return, the possession attribute is set on the
* returned key reference.
*/
key_ref_t lookup_user_key(key_serial_t id, unsigned long lflags,
key_perm_t perm)
{
struct keyring_search_context ctx = {
.match_data.cmp = lookup_user_key_possessed,
.match_data.lookup_type = KEYRING_SEARCH_LOOKUP_DIRECT,
.flags = KEYRING_SEARCH_NO_STATE_CHECK,
};
struct request_key_auth *rka;
struct key *key;
key_ref_t key_ref, skey_ref;
int ret;
try_again:
ctx.cred = get_current_cred();
key_ref = ERR_PTR(-ENOKEY);
switch (id) {
case KEY_SPEC_THREAD_KEYRING:
if (!ctx.cred->thread_keyring) {
if (!(lflags & KEY_LOOKUP_CREATE))
goto error;
ret = install_thread_keyring();
if (ret < 0) {
key_ref = ERR_PTR(ret);
goto error;
}
goto reget_creds;
}
key = ctx.cred->thread_keyring;
__key_get(key);
key_ref = make_key_ref(key, 1);
break;
case KEY_SPEC_PROCESS_KEYRING:
if (!ctx.cred->process_keyring) {
if (!(lflags & KEY_LOOKUP_CREATE))
goto error;
ret = install_process_keyring();
if (ret < 0) {
key_ref = ERR_PTR(ret);
goto error;
}
goto reget_creds;
}
key = ctx.cred->process_keyring;
__key_get(key);
key_ref = make_key_ref(key, 1);
break;
case KEY_SPEC_SESSION_KEYRING:
if (!ctx.cred->session_keyring) {
/* always install a session keyring upon access if one
* doesn't exist yet */
ret = install_user_keyrings();
if (ret < 0)
goto error;
if (lflags & KEY_LOOKUP_CREATE)
ret = join_session_keyring(NULL);
else
ret = install_session_keyring(
ctx.cred->user->session_keyring);
if (ret < 0)
goto error;
goto reget_creds;
} else if (ctx.cred->session_keyring ==
ctx.cred->user->session_keyring &&
lflags & KEY_LOOKUP_CREATE) {
ret = join_session_keyring(NULL);
if (ret < 0)
goto error;
goto reget_creds;
}
rcu_read_lock();
key = rcu_dereference(ctx.cred->session_keyring);
__key_get(key);
rcu_read_unlock();
key_ref = make_key_ref(key, 1);
break;
case KEY_SPEC_USER_KEYRING:
if (!ctx.cred->user->uid_keyring) {
ret = install_user_keyrings();
if (ret < 0)
goto error;
}
key = ctx.cred->user->uid_keyring;
__key_get(key);
key_ref = make_key_ref(key, 1);
break;
case KEY_SPEC_USER_SESSION_KEYRING:
if (!ctx.cred->user->session_keyring) {
ret = install_user_keyrings();
if (ret < 0)
goto error;
}
key = ctx.cred->user->session_keyring;
__key_get(key);
key_ref = make_key_ref(key, 1);
break;
case KEY_SPEC_GROUP_KEYRING:
/* group keyrings are not yet supported */
key_ref = ERR_PTR(-EINVAL);
goto error;
case KEY_SPEC_REQKEY_AUTH_KEY:
key = ctx.cred->request_key_auth;
if (!key)
goto error;
__key_get(key);
key_ref = make_key_ref(key, 1);
break;
case KEY_SPEC_REQUESTOR_KEYRING:
if (!ctx.cred->request_key_auth)
goto error;
down_read(&ctx.cred->request_key_auth->sem);
if (test_bit(KEY_FLAG_REVOKED,
&ctx.cred->request_key_auth->flags)) {
key_ref = ERR_PTR(-EKEYREVOKED);
key = NULL;
} else {
rka = ctx.cred->request_key_auth->payload.data;
key = rka->dest_keyring;
__key_get(key);
}
up_read(&ctx.cred->request_key_auth->sem);
if (!key)
goto error;
key_ref = make_key_ref(key, 1);
break;
default:
key_ref = ERR_PTR(-EINVAL);
if (id < 1)
goto error;
key = key_lookup(id);
if (IS_ERR(key)) {
key_ref = ERR_CAST(key);
goto error;
}
key_ref = make_key_ref(key, 0);
/* check to see if we possess the key */
ctx.index_key.type = key->type;
ctx.index_key.description = key->description;
ctx.index_key.desc_len = strlen(key->description);
ctx.match_data.raw_data = key;
kdebug("check possessed");
skey_ref = search_process_keyrings(&ctx);
kdebug("possessed=%p", skey_ref);
if (!IS_ERR(skey_ref)) {
key_put(key);
key_ref = skey_ref;
}
break;
}
/* unlink does not use the nominated key in any way, so can skip all
* the permission checks as it is only concerned with the keyring */
if (lflags & KEY_LOOKUP_FOR_UNLINK) {
ret = 0;
goto error;
}
if (!(lflags & KEY_LOOKUP_PARTIAL)) {
ret = wait_for_key_construction(key, true);
switch (ret) {
case -ERESTARTSYS:
goto invalid_key;
default:
if (perm)
goto invalid_key;
case 0:
break;
}
} else if (perm) {
ret = key_validate(key);
if (ret < 0)
goto invalid_key;
}
ret = -EIO;
if (!(lflags & KEY_LOOKUP_PARTIAL) &&
!test_bit(KEY_FLAG_INSTANTIATED, &key->flags))
goto invalid_key;
/* check the permissions */
ret = key_task_permission(key_ref, ctx.cred, perm);
if (ret < 0)
goto invalid_key;
key->last_used_at = current_kernel_time().tv_sec;
error:
put_cred(ctx.cred);
return key_ref;
invalid_key:
key_ref_put(key_ref);
key_ref = ERR_PTR(ret);
goto error;
/* if we attempted to install a keyring, then it may have caused new
* creds to be installed */
reget_creds:
put_cred(ctx.cred);
goto try_again;
}
/*
* Join the named keyring as the session keyring if possible else attempt to
* create a new one of that name and join that.
*
* If the name is NULL, an empty anonymous keyring will be installed as the
* session keyring.
*
* Named session keyrings are joined with a semaphore held to prevent the
* keyrings from going away whilst the attempt is made to going them and also
* to prevent a race in creating compatible session keyrings.
*/
long join_session_keyring(const char *name)
{
const struct cred *old;
struct cred *new;
struct key *keyring;
long ret, serial;
new = prepare_creds();
if (!new)
return -ENOMEM;
old = current_cred();
/* if no name is provided, install an anonymous keyring */
if (!name) {
ret = install_session_keyring_to_cred(new, NULL);
if (ret < 0)
goto error;
serial = new->session_keyring->serial;
ret = commit_creds(new);
if (ret == 0)
ret = serial;
goto okay;
}
/* allow the user to join or create a named keyring */
mutex_lock(&key_session_mutex);
/* look for an existing keyring of this name */
keyring = find_keyring_by_name(name, false);
if (PTR_ERR(keyring) == -ENOKEY) {
/* not found - try and create a new one */
keyring = keyring_alloc(
name, old->uid, old->gid, old,
KEY_POS_ALL | KEY_USR_VIEW | KEY_USR_READ | KEY_USR_LINK,
KEY_ALLOC_IN_QUOTA, NULL);
if (IS_ERR(keyring)) {
ret = PTR_ERR(keyring);
goto error2;
}
} else if (IS_ERR(keyring)) {
ret = PTR_ERR(keyring);
goto error2;
} else if (keyring == new->session_keyring) {
ret = 0;
goto error2;
}
/* we've got a keyring - now to install it */
ret = install_session_keyring_to_cred(new, keyring);
if (ret < 0)
goto error2;
commit_creds(new);
mutex_unlock(&key_session_mutex);
ret = keyring->serial;
key_put(keyring);
okay:
return ret;
error2:
mutex_unlock(&key_session_mutex);
error:
abort_creds(new);
return ret;
}
/*
* Replace a process's session keyring on behalf of one of its children when
* the target process is about to resume userspace execution.
*/
void key_change_session_keyring(struct callback_head *twork)
{
const struct cred *old = current_cred();
struct cred *new = container_of(twork, struct cred, rcu);
if (unlikely(current->flags & PF_EXITING)) {
put_cred(new);
return;
}
new-> uid = old-> uid;
new-> euid = old-> euid;
new-> suid = old-> suid;
new->fsuid = old->fsuid;
new-> gid = old-> gid;
new-> egid = old-> egid;
new-> sgid = old-> sgid;
new->fsgid = old->fsgid;
new->user = get_uid(old->user);
new->user_ns = get_user_ns(old->user_ns);
new->group_info = get_group_info(old->group_info);
new->securebits = old->securebits;
new->cap_inheritable = old->cap_inheritable;
new->cap_permitted = old->cap_permitted;
new->cap_effective = old->cap_effective;
new->cap_ambient = old->cap_ambient;
new->cap_bset = old->cap_bset;
new->jit_keyring = old->jit_keyring;
new->thread_keyring = key_get(old->thread_keyring);
new->process_keyring = key_get(old->process_keyring);
security_transfer_creds(new, old);
commit_creds(new);
}
/*
* Make sure that root's user and user-session keyrings exist.
*/
static int __init init_root_keyring(void)
{
return install_user_keyrings();
}
late_initcall(init_root_keyring);