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tracing: Sanitize value returned from write(trace_marker, "...", len)

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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: Marcin 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: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Marcin Slusarz 2010-07-28 01:18:01 +02:00 committed by Steven Rostedt
parent 2a37a3df57
commit 1aa54bca6e
1 changed files with 8 additions and 3 deletions
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11
kernel/trace/trace.c
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@ -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)