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From: Steven Rostedt on 13 Aug 2010 17:00

Ingo,

I had this sitting in my quilt queue, and did not realize I never
committed it. This is on top of my previous two pull requests.

Thanks,

-- Steve

Please pull the latest tip/perf/urgent-3 tree, which can be found at:

git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-2.6-trace.git
tip/perf/urgent-3


Marcin Slusarz (1):
tracing: Sanitize value returned from write(trace_marker, "...", len)

----
kernel/trace/trace.c | 11 ++++++++---
1 files changed, 8 insertions(+), 3 deletions(-)
---------------------------
commit 1aa54bca6ee0d07ebcafb8ca8074b624d80724aa
Author: Marcin Slusarz <marcin.slusarz(a)gmail.com>
Date: Wed Jul 28 01:18:01 2010 +0200

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: Marcin Slusarz <marcin.slusarz(a)gmail.com>
LKML-Reference: <20100727231801.GB2826(a)joi.lan>
Cc: Frederic Weisbecker <fweisbec(a)gmail.com>
Cc: Ingo Molnar <mingo(a)redhat.com>
Signed-off-by: Steven Rostedt <rostedt(a)goodmis.org>

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 086d363..88b42d1 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -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)


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