[PATCH 0/2] Begin auditing SECCOMP_RET_ERRNO return actions

[Paul Moore]

On Tue, Jan 3, 2017 at 4:03 PM, Kees Cook <keescook at chromium.org> wrote:
> On Tue, Jan 3, 2017 at 12:54 PM, Paul Moore <paul at paul-moore.com> wrote:
>> On Tue, Jan 3, 2017 at 3:44 PM, Kees Cook <keescook at chromium.org> wrote:
>>> I still wonder, though, isn't there a way to use auditctl to get all
>>> the seccomp messages you need?
>>
>> Not all of the seccomp actions are currently logged, that's one of the
>> problems (and the biggest at the moment).
>
> Well... sort of. It all gets passed around, but the logic isn't very
> obvious (or at least I always have to go look it up).

Last time I checked SECCOMP_RET_ALLOW wasn't logged (as well as at
least one other action, but I can't remember which off the top of my
head)?

> include/linux/audit.h:
>
> #ifdef CONFIG_AUDITSYSCALL
> ...
> static inline void audit_seccomp(unsigned long syscall, long signr, int code)
> {
>         if (!audit_enabled)
>                 return;
>
>         /* Force a record to be reported if a signal was delivered. */
>         if (signr || unlikely(!audit_dummy_context()))
>                 __audit_seccomp(syscall, signr, code);
> }
> ...
> #else /* CONFIG_AUDITSYSCALL */
>
> static inline void audit_seccomp(unsigned long syscall, long signr, int code)
> { }
> ...
> #endif
>
> kernel/seccomp.c:
>
>         switch (action) {
>         case SECCOMP_RET_ERRNO:
>                 /* Set low-order bits as an errno, capped at MAX_ERRNO. */
>                 if (data > MAX_ERRNO)
>                         data = MAX_ERRNO;
>                 syscall_set_return_value(current, task_pt_regs(current),
>                                          -data, 0);
>                 goto skip;
> ...
>         case SECCOMP_RET_KILL:
>         default:
>                 audit_seccomp(this_syscall, SIGSYS, action);
>                 do_exit(SIGSYS);
>         }
>
>         unreachable();
>
> skip:
>         audit_seccomp(this_syscall, 0, action);
>
>
> Current state:
>
> - if CONFIG_AUDITSYSCALL=n, then nothing is ever reported.
>
> - if audit is disabled, nothing is ever reported.
>
> - if a process isn't being specifically audited
> (!audit_dummy_context()), only signals (RET_KILL) are reported.
>
> - when being specifically audited, everything is reported.
>
>
> So, shouldn't it be possible to specifically audit a process and
> examine the resulting logs for the RET_* level one is interested in
> ("code=0x%x" in __audit_seccomp())?
>
> -Kees
>
> --
> Kees Cook
> Nexus Security



-- 
paul moore
www.paul-moore.com