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Commit 1aa54bca authored by Marcin Slusarz's avatar Marcin Slusarz Committed by Steven Rostedt
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tracing: Sanitize value returned from write(trace_marker, "...", len) 



When userspace code writes non-new-line-terminated string to trace_marker
file, write handler appends new-line and returns number of bytes written
to trace buffer, so
write(fd, "abc", 3) will return 4

That's unexpected and unfortunately it confuses glibc's fprintf function.

Example:
int main() {
  fprintf(stderr, "abc");
  return 0;
}

$ gcc test.c -o test
$ echo mmiotrace > /sys/kernel/debug/tracing/current_tracer
$ ./test 2>/sys/kernel/debug/tracing/trace_marker

results in infinite loop:
write(fd, "abc", 3) = 4
write(fd, "", 1) = 0
write(fd, "", 1) = 0
write(fd, "", 1) = 0
write(fd, "", 1) = 0
write(fd, "", 1) = 0
write(fd, "", 1) = 0
write(fd, "", 1) = 0
(...)

...and kernel trace buffer full of empty markers.

Fix it by sanitizing write return value.

Signed-off-by: default avatarMarcin Slusarz <marcin.slusarz@gmail.com>
LKML-Reference: <20100727231801.GB2826@joi.lan>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
parent 2a37a3df

kernel/trace/trace.c

+8 −3
Original line number Diff line number Diff line
@@ -3498,6 +3498,7 @@ tracing_mark_write(struct file *filp, const char __user *ubuf, 
					size_t cnt, loff_t *fpos)

{

	char *buf;

	size_t written;



	if (tracing_disabled)

		return -EINVAL;
@@ -3519,11 +3520,15 @@ tracing_mark_write(struct file *filp, const char __user *ubuf, 
	} else

		buf[cnt] = '\0';



	cnt = mark_printk("%s", buf);

	written = mark_printk("%s", buf);

	kfree(buf);

	*fpos += cnt;

	*fpos += written;



	return cnt;

	/* don't tell userspace we wrote more - it might confuse them */

	if (written > cnt)

		written = cnt;



	return written;

}



static int tracing_clock_show(struct seq_file *m, void *v)