audit: Make testing for a valid loginuid explicit.

audit rule additions containing "-F auid!=4294967295" were failing
with EINVAL because of a regression caused by e1760bd.

Apparently some userland audit rule sets want to know if loginuid uid
has been set and are using a test for auid != 4294967295 to determine
that.

In practice that is a horrible way to ask if a value has been set,
because it relies on subtle implementation details and will break
every time the uid implementation in the kernel changes.

So add a clean way to test if the audit loginuid has been set, and
silently convert the old idiom to the cleaner and more comprehensible
new idiom.

Cc: <stable@vger.kernel.org> # 3.7
Reported-By: Richard Guy Briggs <rgb@redhat.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Tested-by: Richard Guy Briggs <rgb@redhat.com>
Signed-off-by: Eric Paris <eparis@redhat.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/include/linux/audit.h b/include/linux/audit.h
index 469d11755e46..b20b03852f21 100644
--- a/include/linux/audit.h
+++ b/include/linux/audit.h
@@ -391,6 +391,11 @@ static inline void audit_ptrace(struct task_struct *t)
 #define audit_signals 0
 #endif /* CONFIG_AUDITSYSCALL */
 
+static inline bool audit_loginuid_set(struct task_struct *tsk)
+{
+        return uid_valid(audit_get_loginuid(tsk));
+}
+
 #ifdef CONFIG_AUDIT
 /* These are defined in audit.c */
                                 /* Public API */