io_uring: don't audit the capability check in io_uring_create()

The check being unconditional may lead to unwanted denials reported by
LSMs when a process has the capability granted by DAC, but denied by an
LSM. In the case of SELinux such denials are a problem, since they can't
be effectively filtered out via the policy and when not silenced, they
produce noise that may hide a true problem or an attack.

Since not having the capability merely means that the created io_uring
context will be accounted against the current user's RLIMIT_MEMLOCK
limit, we can disable auditing of denials for this check by using
ns_capable_noaudit() instead of capable().

Fixes: 2b188cc1bb ("Add io_uring IO interface")
Link: https://bugzilla.redhat.com/show_bug.cgi?id=2193317
Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
Link: https://lore.kernel.org/r/20230718115607.65652-1-omosnace@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/io_uring.c

@@ -3870,7 +3870,7 @@ static __cold int io_uring_create(unsigned entries, struct io_uring_params *p,
 		ctx->syscall_iopoll = 1;
 
 	ctx->compat = in_compat_syscall();
-	if (!capable(CAP_IPC_LOCK))
+	if (!ns_capable_noaudit(&init_user_ns, CAP_IPC_LOCK))
 		ctx->user = get_uid(current_user());
 
 	/*