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audit: Record fanotify access control decisions

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The fanotify interface allows user space daemons to make access
control decisions. Under common criteria requirements, we need to
optionally record decisions based on policy. This patch adds a bit mask,
FAN_AUDIT, that a user space daemon can 'or' into the response decision
which will tell the kernel that it made a decision and record it.

It would be used something like this in user space code:

  response.response = FAN_DENY | FAN_AUDIT;
  write(fd, &response, sizeof(struct fanotify_response));

When the syscall ends, the audit system will record the decision as a
AUDIT_FANOTIFY auxiliary record to denote that the reason this event
occurred is the result of an access control decision from fanotify
rather than DAC or MAC policy.

A sample event looks like this:

type=PATH msg=audit(1504310584.332:290): item=0 name="./evil-ls"
inode=1319561 dev=fc:03 mode=0100755 ouid=1000 ogid=1000 rdev=00:00
obj=unconfined_u:object_r:user_home_t:s0 nametype=NORMAL
type=CWD msg=audit(1504310584.332:290): cwd="/home/sgrubb"
type=SYSCALL msg=audit(1504310584.332:290): arch=c000003e syscall=2
success=no exit=-1 a0=32cb3fca90 a1=0 a2=43 a3=8 items=1 ppid=901
pid=959 auid=1000 uid=1000 gid=1000 euid=1000 suid=1000
fsuid=1000 egid=1000 sgid=1000 fsgid=1000 tty=pts1 ses=3 comm="bash"
exe="/usr/bin/bash" subj=unconfined_u:unconfined_r:unconfined_t:
s0-s0:c0.c1023 key=(null)
type=FANOTIFY msg=audit(1504310584.332:290): resp=2

Prior to using the audit flag, the developer needs to call
fanotify_init or'ing in FAN_ENABLE_AUDIT to ensure that the kernel
supports auditing. The calling process must also have the CAP_AUDIT_WRITE
capability.

Signed-off-by: sgrubb <sgrubb@redhat.com>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
This commit is contained in:
Steve Grubb 2017-10-02 20:21:39 -04:00 committed by Jan Kara
parent 8a5776a5f4
commit de8cd83e91
8 changed files with 46 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
fs/notify/fanotify/fanotify.c
View File

@ -9,6 +9,7 @@
#include <linux/sched/user.h>
#include <linux/types.h>
#include <linux/wait.h>
#include <linux/audit.h>
#include "fanotify.h"
@ -78,7 +79,7 @@ static int fanotify_get_response(struct fsnotify_group *group,
fsnotify_finish_user_wait(iter_info);
out:
/* userspace responded, convert to something usable */
switch (event->response) {
switch (event->response & ~FAN_AUDIT) {
case FAN_ALLOW:
ret = 0;
break;
@ -86,6 +87,11 @@ out:
default:
ret = -EPERM;
}
/* Check if the response should be audited */
if (event->response & FAN_AUDIT)
audit_fanotify(event->response & ~FAN_AUDIT);
event->response = 0;
pr_debug("%s: group=%p event=%p about to return ret=%d\n", __func__,

16
fs/notify/fanotify/fanotify_user.c
View File

@ -179,7 +179,7 @@ static int process_access_response(struct fsnotify_group *group,
* userspace can send a valid response or we will clean it up after the
* timeout
*/
switch (response) {
switch (response & ~FAN_AUDIT) {
case FAN_ALLOW:
case FAN_DENY:
break;
@ -190,6 +190,9 @@ static int process_access_response(struct fsnotify_group *group,
if (fd < 0)
return -EINVAL;
if ((response & FAN_AUDIT) && !group->fanotify_data.audit)
return -EINVAL;
event = dequeue_event(group, fd);
if (!event)
return -ENOENT;
@ -721,7 +724,11 @@ SYSCALL_DEFINE2(fanotify_init, unsigned int, flags, unsigned int, event_f_flags)
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
#ifdef CONFIG_AUDITSYSCALL
if (flags & ~(FAN_ALL_INIT_FLAGS | FAN_ENABLE_AUDIT))
#else
if (flags & ~FAN_ALL_INIT_FLAGS)
#endif
return -EINVAL;
if (event_f_flags & ~FANOTIFY_INIT_ALL_EVENT_F_BITS)
@ -805,6 +812,13 @@ SYSCALL_DEFINE2(fanotify_init, unsigned int, flags, unsigned int, event_f_flags)
group->fanotify_data.max_marks = FANOTIFY_DEFAULT_MAX_MARKS;
}
if (flags & FAN_ENABLE_AUDIT) {
fd = -EPERM;
if (!capable(CAP_AUDIT_WRITE))
goto out_destroy_group;
group->fanotify_data.audit = true;
}
fd = anon_inode_getfd("[fanotify]", &fanotify_fops, group, f_flags);
if (fd < 0)
goto out_destroy_group;

3
fs/notify/fdinfo.c
View File

@ -156,6 +156,9 @@ void fanotify_show_fdinfo(struct seq_file *m, struct file *f)
if (group->fanotify_data.max_marks == UINT_MAX)
flags |= FAN_UNLIMITED_MARKS;
if (group->fanotify_data.audit)
flags |= FAN_ENABLE_AUDIT;
seq_printf(m, "fanotify flags:%x event-flags:%x\n",
flags, group->fanotify_data.f_flags);

10
include/linux/audit.h
View File

@ -356,6 +356,7 @@ extern int __audit_log_bprm_fcaps(struct linux_binprm *bprm,
extern void __audit_log_capset(const struct cred *new, const struct cred *old);
extern void __audit_mmap_fd(int fd, int flags);
extern void __audit_log_kern_module(char *name);
extern void __audit_fanotify(unsigned int response);
static inline void audit_ipc_obj(struct kern_ipc_perm *ipcp)
{
@ -452,6 +453,12 @@ static inline void audit_log_kern_module(char *name)
__audit_log_kern_module(name);
}
static inline void audit_fanotify(unsigned int response)
{
if (!audit_dummy_context())
__audit_fanotify(response);
}
extern int audit_n_rules;
extern int audit_signals;
#else /* CONFIG_AUDITSYSCALL */
@ -568,6 +575,9 @@ static inline void audit_log_kern_module(char *name)
{
}
static inline void audit_fanotify(unsigned int response)
{ }
static inline void audit_ptrace(struct task_struct *t)
{ }
#define audit_n_rules 0

1
include/linux/fsnotify_backend.h
View File

@ -190,6 +190,7 @@ struct fsnotify_group {
int f_flags;
unsigned int max_marks;
struct user_struct *user;
bool audit;
} fanotify_data;
#endif /* CONFIG_FANOTIFY */
};

1
include/uapi/linux/audit.h
View File

@ -112,6 +112,7 @@
#define AUDIT_FEATURE_CHANGE 1328 /* audit log listing feature changes */
#define AUDIT_REPLACE 1329 /* Replace auditd if this packet unanswerd */
#define AUDIT_KERN_MODULE 1330 /* Kernel Module events */
#define AUDIT_FANOTIFY 1331 /* Fanotify access decision */
#define AUDIT_AVC 1400 /* SE Linux avc denial or grant */
#define AUDIT_SELINUX_ERR 1401 /* Internal SE Linux Errors */

3
include/uapi/linux/fanotify.h
View File

@ -35,6 +35,7 @@
#define FAN_UNLIMITED_QUEUE 0x00000010
#define FAN_UNLIMITED_MARKS 0x00000020
#define FAN_ENABLE_AUDIT 0x00000040
#define FAN_ALL_INIT_FLAGS (FAN_CLOEXEC | FAN_NONBLOCK | \
FAN_ALL_CLASS_BITS | FAN_UNLIMITED_QUEUE |\
@ -99,6 +100,8 @@ struct fanotify_response {
/* Legit userspace responses to a _PERM event */
#define FAN_ALLOW 0x01
#define FAN_DENY 0x02
#define FAN_AUDIT 0x10 /* Bit mask to create audit record for result */
/* No fd set in event */
#define FAN_NOFD -1

6
kernel/auditsc.c
View File

@ -2390,6 +2390,12 @@ void __audit_log_kern_module(char *name)
context->type = AUDIT_KERN_MODULE;
}
void __audit_fanotify(unsigned int response)
{
audit_log(current->audit_context, GFP_KERNEL,
AUDIT_FANOTIFY, "resp=%u", response);
}
static void audit_log_task(struct audit_buffer *ab)
{
kuid_t auid, uid;