Fix broken audit tests for exec arg len

The "fix" in commit 0b08c5e5944 ("audit: Fix check of return value of
strnlen_user()") didn't fix anything, it broke things.  As reported by
Steven Rostedt:

 "Yes, strnlen_user() returns 0 on fault, but if you look at what len is
  set to, than you would notice that on fault len would be -1"

because we just subtracted one from the return value.  So testing
against 0 doesn't test for a fault condition, it tests against a
perfectly valid empty string.

Also fix up the usual braindamage wrt using WARN_ON() inside a
conditional - make it part of the conditional and remove the explicit
unlikely() (which is already part of the WARN_ON*() logic, exactly so
that you don't have to write unreadable code.

Reported-and-tested-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Paul Moore <pmoore@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/kernel/auditsc.c b/kernel/auditsc.c
index 09c65640cad6156f0ea702bc32ba9847b9465249..e85bdfd15fedd4c8fed46818edae6191673bff07 100644 (file)
--- a/kernel/auditsc.c
+++ b/kernel/auditsc.c
@@ -1021,8 +1021,7 @@ static int audit_log_single_execve_arg(struct audit_context *context,
         * for strings that are too long, we should not have created
         * any.
         */
-       if (unlikely((len == 0) || len > MAX_ARG_STRLEN - 1)) {
-               WARN_ON(1);
+       if (WARN_ON_ONCE(len < 0 || len > MAX_ARG_STRLEN - 1)) {
                send_sig(SIGKILL, current, 0);
                return -1;
        }