audit: Record fanotify access control decisions

Forwarding a copy due to a copy & paste error

---------- Forwarded Message ----------

Subject: [PATCH v6 1/1] audit: Record fanotify access control decisions
Date: Tuesday, September 26, 2017, 5:11:48 PM EDT
From: Steve Grubb <[email protected]>
To: fsdevel <[email protected]>
CC: Linux Audit <[email protected]>, [email protected], Jan Kara <[email protected]>, Amir Goldstein <[email protected]>, Paul Moore <[email protected]>

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_ENABLE_AUDIT to ensure that the kernel supports auditing. The calling process must also have the CAP_AUDIT_WRITE capability.

* This v6 update adds empty inline audit_fanotify function for when CONFIG_AUDITSYSCALL is not defined.

---
 fs/notify/fanotify/fanotify.c      |  8 +++++++-
 fs/notify/fanotify/fanotify_user.c | 16 +++++++++++++++-
 fs/notify/fdinfo.c                 |  3 +++
 include/linux/audit.h              | 10 ++++++++++
 include/linux/fsnotify_backend.h   |  1 +
 include/uapi/linux/audit.h         |  1 +
 include/uapi/linux/fanotify.h      |  3 +++
 kernel/auditsc.c                   |  6 ++++++
 8 files changed, 46 insertions(+), 2 deletions(-)

index 2fa99ae..1968d21 100644
@@ -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__,

fanotify_user.c
index 907a481..ea3c458 100644

@@ -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_enabled)
+ 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_enabled = true;
+ }
+
fd = anon_inode_getfd("[fanotify]", &fanotify_fops, group, f_flags); if (fd < 0)
goto out_destroy_group;

index dd63aa9..ed311e3 100644
@@ -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_enabled)
+ flags |= FAN_ENABLE_AUDIT;
+
seq_printf(m, "fanotify flags:%x event-flags:%x\n",
flags, group->fanotify_data.f_flags);

index 2150bdc..9095617 100644
@@ -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 */
@@ -572,6 +579,9 @@ 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

fsnotify_backend.h
index c6c6931..f4131f2 100644

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

index 0714a66..221f8b7 100644
@@ -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 */

index 030508d..5dda19a 100644
@@ -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
 

index 3260ba2..e046de8 100644
@@ -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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