revert: 1320a4052e ("audit: trigger accompanying records when no rules present")

Unfortunately the commit listed in the subject line above failed
to ensure that the task's audit_context was properly initialized/set
before enabling the "accompanying records".  Depending on the
situation, the resulting audit_context could have invalid values in
some of it's fields which could cause a kernel panic/oops when the
task/syscall exists and the audit records are generated.

We will revisit the original patch, with the necessary fixes, in a
future kernel but right now we just want to fix the kernel panic
with the least amount of added risk.

Cc: stable@vger.kernel.org
Fixes: 1320a4052e ("audit: trigger accompanying records when no rules present")
Reported-by: j2468h@googlemail.com
Signed-off-by: Paul Moore <paul@paul-moore.com>

kernel/audit.c

@@ -1848,7 +1848,6 @@ struct audit_buffer *audit_log_start(struct audit_context *ctx, gfp_t gfp_mask,
 	}
 
 	audit_get_stamp(ab->ctx, &t, &serial);
-	audit_clear_dummy(ab->ctx);
 	audit_log_format(ab, "audit(%llu.%03lu:%u): ",
 			 (unsigned long long)t.tv_sec, t.tv_nsec/1000000, serial);
 

kernel/audit.h

@@ -290,13 +290,6 @@ extern int audit_signal_info_syscall(struct task_struct *t);
 extern void audit_filter_inodes(struct task_struct *tsk,
 				struct audit_context *ctx);
 extern struct list_head *audit_killed_trees(void);
-
-static inline void audit_clear_dummy(struct audit_context *ctx)
-{
-	if (ctx)
-		ctx->dummy = 0;
-}
-
 #else /* CONFIG_AUDITSYSCALL */
 #define auditsc_get_stamp(c, t, s) 0
 #define audit_put_watch(w) {}
@@ -330,7 +323,6 @@ static inline int audit_signal_info_syscall(struct task_struct *t)
 }
 
 #define audit_filter_inodes(t, c) AUDIT_DISABLED
-#define audit_clear_dummy(c) {}
 #endif /* CONFIG_AUDITSYSCALL */
 
 extern char *audit_unpack_string(void **bufp, size_t *remain, size_t len);

kernel/auditsc.c

@@ -1417,6 +1417,9 @@ static void audit_log_proctitle(void)
 	struct audit_context *context = audit_context();
 	struct audit_buffer *ab;
 
+	if (!context || context->dummy)
+		return;
+
 	ab = audit_log_start(context, GFP_KERNEL, AUDIT_PROCTITLE);
 	if (!ab)
 		return;	/* audit_panic or being filtered */