Hello,
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_AUDIT_ENABLE to ensure that the kernel
supports auditing. The calling process must also have the CAP_AUDIT_WRITE
capability.
Signed-off-by: sgrubb <sgrubb@xxxxxxxxxx>
---
fs/notify/fanotify/fanotify.c | 8 +++++++-
fs/notify/fanotify/fanotify_user.c | 12 +++++++++++-
include/linux/audit.h | 7 +++++++
include/linux/fsnotify_backend.h | 1 +
include/uapi/linux/audit.h | 1 +
include/uapi/linux/fanotify.h | 5 ++++-
kernel/auditsc.c | 6 ++++++
7 files changed, 37 insertions(+), 3 deletions(-)
diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
index 2fa99ae..1968d21 100644
--- a/fs/notify/fanotify/fanotify.c
+++ b/fs/notify/fanotify/fanotify.c
@@ -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 @@ static int fanotify_get_response(struct fsnotify_group *group,
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__,
diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
index 907a481..231db8b 100644
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -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->audit_enabled == 0))
+ return -EINVAL;
+
event = dequeue_event(group, fd);
if (!event)
return -ENOENT;
@@ -805,6 +808,13 @@ 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->audit_enabled = 1;
+ }
+
fd = anon_inode_getfd("[fanotify]", &fanotify_fops, group, f_flags);
if (fd < 0)
goto out_destroy_group;
diff --git a/include/linux/audit.h b/include/linux/audit.h
index 2150bdc..bf55732 100644
--- a/include/linux/audit.h
+++ b/include/linux/audit.h
@@ -360,6 +360,7 @@ 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)
{
@@ -456,6 +457,12 @@ 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 */
diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
index c6c6931..8f7ea68 100644
--- a/include/linux/fsnotify_backend.h
+++ b/include/linux/fsnotify_backend.h
@@ -193,6 +193,7 @@ struct fsnotify_group {
} fanotify_data;
#endif /* CONFIG_FANOTIFY */
};
+ unsigned int audit_enabled;
};
/* when calling fsnotify tell it if the data is a path or inode */
diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
index 0714a66..221f8b7 100644
--- a/include/uapi/linux/audit.h
+++ b/include/uapi/linux/audit.h
@@ -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 */
diff --git a/include/uapi/linux/fanotify.h b/include/uapi/linux/fanotify.h
index 030508d..46bb431 100644
--- a/include/uapi/linux/fanotify.h
+++ b/include/uapi/linux/fanotify.h
@@ -35,10 +35,11 @@
#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 |\
- FAN_UNLIMITED_MARKS)
+ FAN_UNLIMITED_MARKS | FAN_ENABLE_AUDIT)
/* flags used for fanotify_modify_mark() */
#define FAN_MARK_ADD 0x00000001
@@ -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
diff --git a/kernel/auditsc.c b/kernel/auditsc.c
index 3260ba2..e046de8 100644
--- a/kernel/auditsc.c
+++ b/kernel/auditsc.c
@@ -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;
--
2.9.5
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