[PATCH ghak82] audit: Fix wrong task in comparison of session ID

[Paul Moore]

On Thu, May 17, 2018 at 11:31 AM, Ondrej Mosnacek <omosnace at redhat.com> wrote:
> The audit_filter_rules() function in auditsc.c compared the session ID
> with the credentials of the current task, while it should use the
> credentials of the task given to audit_filter_rules() as a parameter
> (tsk).
>
> GitHub issue:
> https://github.com/linux-audit/audit-kernel/issues/82
>
> Fixes: 8fae47705685 ("audit: add support for session ID user filter")
> Cc: stable at vger.kernel.org
> Signed-off-by: Ondrej Mosnacek <omosnace at redhat.com>
> ---
>  kernel/auditsc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Good catch.  However, I'm not completely convinced this is stable material.

This bug really only affects "task" filters which I believe to be
fairly limited in the wild, due to the limited number of fields that
one can filter on.  Every other filter, including the "exit" filter,
work as expected (which is why the audit-testsuite didn't catch this
bug).  Further, even in the case of the task filter, the *only* time
where the current session ID would be different from the tsk session
ID is in the case of a login event, but even in this case the two
values should be equal during the "task" filtering as you can't change
the login-ID/session-ID until after you have successfully
fork()'d/clone()'d the new task.

I'll hold off on merging this in case I'm missing some even more
subtle point that you've found.  From what I can tell this is a good
fix, but not something an actual user would ever really encounter and
therefore not something that warrants inclusion in stable.

> diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> index ec38e4d97c23..6d577a34b16b 100644
> --- a/kernel/auditsc.c
> +++ b/kernel/auditsc.c
> @@ -513,7 +513,7 @@ static int audit_filter_rules(struct task_struct *tsk,
>                         result = audit_gid_comparator(cred->fsgid, f->op, f->gid);
>                         break;
>                 case AUDIT_SESSIONID:
> -                       sessionid = audit_get_sessionid(current);
> +                       sessionid = audit_get_sessionid(tsk);
>                         result = audit_comparator(sessionid, f->op, f->val);
>                         break;
>                 case AUDIT_PERS:
> --
> 2.17.0

-- 
paul moore
www.paul-moore.com