selinux: add tracepoint on audited events
The audit data currently captures which process and which target
is responsible for a denial. There is no data on where exactly in the
process that call occurred. Debugging can be made easier by being able to
reconstruct the unified kernel and userland stack traces [1]. Add a
tracepoint on the SELinux denials which can then be used by userland
(i.e. perf).
Although this patch could manually be added by each OS developer to
trouble shoot a denial, adding it to the kernel streamlines the
developers workflow.
It is possible to use perf for monitoring the event:
# perf record -e avc:selinux_audited -g -a
^C
# perf report -g
[...]
6.40% 6.40% audited=800000 tclass=4
|
__libc_start_main
|
|--4.60%--__GI___ioctl
| entry_SYSCALL_64
| do_syscall_64
| __x64_sys_ioctl
| ksys_ioctl
| binder_ioctl
| binder_set_nice
| can_nice
| capable
| security_capable
| cred_has_capability.isra.0
| slow_avc_audit
| common_lsm_audit
| avc_audit_post_callback
| avc_audit_post_callback
|
It is also possible to use the ftrace interface:
# echo 1 > /sys/kernel/debug/tracing/events/avc/selinux_audited/enable
# cat /sys/kernel/debug/tracing/trace
tracer: nop
entries-in-buffer/entries-written: 1/1 #P:8
[...]
dmesg-3624 [001] 13072.325358: selinux_denied: audited=800000 tclass=4
The tclass value can be mapped to a class by searching
security/selinux/flask.h. The audited value is a bit field of the
permissions described in security/selinux/av_permissions.h for the
corresponding class.
[1] https://source.android.com/devices/tech/debug/native_stack_dump
Signed-off-by: Thiébaud Weksteen <tweek@google.com>
Suggested-by: Joel Fernandes <joelaf@google.com>
Reviewed-by: Peter Enderborg <peter.enderborg@sony.com>
Acked-by: Stephen Smalley <stephen.smalley.work@gmail.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>
diff --git a/security/selinux/avc.c b/security/selinux/avc.c
index d18cb32..b0a0af7 100644
--- a/security/selinux/avc.c
+++ b/security/selinux/avc.c
@@ -31,6 +31,9 @@
#include "avc_ss.h"
#include "classmap.h"
+#define CREATE_TRACE_POINTS
+#include <trace/events/avc.h>
+
#define AVC_CACHE_SLOTS 512
#define AVC_DEF_CACHE_THRESHOLD 512
#define AVC_CACHE_RECLAIM 16
@@ -706,6 +709,8 @@ static void avc_audit_post_callback(struct audit_buffer *ab, void *a)
u32 scontext_len;
int rc;
+ trace_selinux_audited(sad);
+
rc = security_sid_to_context(sad->state, sad->ssid, &scontext,
&scontext_len);
if (rc)
