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audit: Record fanotify access control decisions 

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;