audit: Fix check of return value of strnlen_user()

audit: Fix check of return value of strnlen_user()

Orabug: 25308127

[ Upstream commit 0b08c5e59441d08ab4b5e72afefd5cd98a4d83df ]

strnlen_user() returns 0 when it hits fault, not -1. Fix the test in
audit_log_single_execve_arg(). Luckily this shouldn't ever happen unless
there's a kernel bug so it's mostly a cosmetic fix.

CC: Paul Moore <pmoore@redhat.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Paul Moore <pmoore@redhat.com>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
(cherry picked from commit a49b282f08d96cd73838e4e1a5ace747d432ba7d)
Signed-off-by: Dhaval Giani <dhaval.giani@oracle.com>