PATCH: ausearch doesn't correcly act as a filter when no EOF on input

This was filed as a bug in our bugzilla.

works : cat /var/log/audit/audit.log | ausearch -i -if /dev/stdin | cat
doesnt: tail -f /var/log/audit/audit.log | ausearch -i -if /dev/stdin | cat

Obviously it's a contrived example, they have more interesting processes each
side of the filter. Issue is that tail -f never indicates EOF and if ausearch
stdout is a pipe (versus a file), the output can remain queued in the pipebuf.

Following patch fixes it, or a simpler patch could unconditionally flush stdout.

I've not looked for similar issues elsewhere.

Tony

@@ -58,11 +58,11 @@
 extern int match(llist *l);
 extern void output_record(llist *l);
 
-static int input_is_pipe(void)
+static int is_pipe(int fd)
 {
 	struct stat st;
 
-	if (fstat(0, &st) == 0) {
+	if (fstat(fd, &st) == 0) {
 		if (S_ISFIFO(st.st_mode)) 
 			pipe_mode = 1;
 	}

@@ -92,7 +92,7 @@
 		rc = process_file(user_file);
 	else if (force_logs)
 		rc = process_logs();
-	else if (input_is_pipe())
+	else if (is_pipe(0))
 		rc = process_stdin();
 	else
 		rc = process_logs();

@@ -175,6 +175,7 @@
 {
 	llist entries; // entries in a record
 	int ret;
+	int flush = is_pipe(1);
 
 	/* For each record in file */
 	list_create(&entries);

@@ -185,6 +186,8 @@
 		}
 		if (match(&entries)) {
 			output_record(&entries);
+			if (flush) 
+				fflush(stdout);
 			found = 1;
 			if (just_one) {
 				list_clear(&entries);

The general problem is a little bigger. ausearch can't tell when an event is complete. It assumes that the kernel serializes things - which it doesn't. With files, it flushes everything when it hits EOF. But pipes don't have that. The solution I was going to implement was to start a timer when the input is a pipe and timeout the currently accumulating event. Flushing the output if using a pipe looks like a good measure, too.

I'd rather not flush all the time otherwise the performance improvement of buffering is lost. I currently have ausearch completely tore apart to rework its event collection logic so that interlaced events are assembled correctly and completely. Maybe in a few days I can revisit this problem.

aureport shares much of the same IO design and the auparse library also does not use clock time to finish off events if the input is a pipe.

-Steve

Applied in commit #190.

-Steve