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>
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 @@
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 @@
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..0455ea7 100644
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -179,7 +179,7 @@
* 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 @@
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 @@
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 @@
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;
diff --git a/fs/notify/fdinfo.c b/fs/notify/fdinfo.c
index dd63aa9..645ab56 100644
--- a/fs/notify/fdinfo.c
+++ b/fs/notify/fdinfo.c
@@ -156,6 +156,9 @@
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);
diff --git a/include/linux/audit.h b/include/linux/audit.h
index cb708eb..d66220d 100644
--- a/include/linux/audit.h
+++ b/include/linux/audit.h
@@ -356,6 +356,7 @@
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 @@
__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_fanotify(unsigned int response)
+{ }
+
static inline void audit_ptrace(struct task_struct *t)
{ }
#define audit_n_rules 0
diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
index c6c6931..4a474f9 100644
--- a/include/linux/fsnotify_backend.h
+++ b/include/linux/fsnotify_backend.h
@@ -190,6 +190,7 @@
int f_flags;
unsigned int max_marks;
struct user_struct *user;
+ bool audit;
} fanotify_data;
#endif /* CONFIG_FANOTIFY */
};
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..5dda19a 100644
--- a/include/uapi/linux/fanotify.h
+++ b/include/uapi/linux/fanotify.h
@@ -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 @@
/* 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 ecc23e2..9c723e9 100644
--- a/kernel/auditsc.c
+++ b/kernel/auditsc.c
@@ -2390,6 +2390,12 @@
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;