On 8/17/20 1:07 PM, Thiébaud Weksteen wrote:
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@xxxxxxxxxx>
Suggested-by: Joel Fernandes <joelaf@xxxxxxxxxx>
Reviewed-by: Peter Enderborg <peter.enderborg@xxxxxxxx>
Acked-by: Stephen Smalley <stephen.smalley.work@xxxxxxxxx>
