fix oops in __audit_signal_info()

The check for audit_signals is misplaced and the check for
audit_dummy_context() is missing; as the result, if we send a signal to
auditd from task with NULL ->audit_context while we have audit_signals
!= 0 we end up with an oops.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Acked-by: James Morris <jmorris@namei.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/auditsc.c

@@ -1992,8 +1992,8 @@ int __audit_signal_info(int sig, struct task_struct *t)
 	extern uid_t audit_sig_uid;
 	extern u32 audit_sig_sid;
 
-	if (audit_pid && t->tgid == audit_pid &&
-	    (sig == SIGTERM || sig == SIGHUP || sig == SIGUSR1)) {
+	if (audit_pid && t->tgid == audit_pid) {
+		if (sig == SIGTERM || sig == SIGHUP || sig == SIGUSR1) {
 			audit_sig_pid = tsk->pid;
 			if (ctx)
 				audit_sig_uid = ctx->loginuid;
@@ -2001,9 +2001,9 @@ int __audit_signal_info(int sig, struct task_struct *t)
 				audit_sig_uid = tsk->uid;
 			selinux_get_task_sid(tsk, &audit_sig_sid);
 		}
-
-	if (!audit_signals) /* audit_context checked in wrapper */
+		if (!audit_signals || audit_dummy_context())
 			return 0;
+	}
 
 	/* optimize the common case by putting first signal recipient directly
 	 * in audit_context */