Patch "tracing/filter: Do not allow infix to exceed end of string" has been added to the 3.14-stable tree

This is a note to let you know that I've just added the patch titled

tracing/filter: Do not allow infix to exceed end of string

to the 3.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
tracing-filter-do-not-allow-infix-to-exceed-end-of-string.patch
and it can be found in the queue-3.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: "Steven Rostedt (Red Hat)" <[email protected]>
Date: Thu, 25 Jun 2015 18:10:09 -0400
Subject: tracing/filter: Do not allow infix to exceed end of string

From: "Steven Rostedt (Red Hat)" <[email protected]>

commit 6b88f44e161b9ee2a803e5b2b1fbcf4e20e8b980 upstream.

While debugging a WARN_ON() for filtering, I found that it is possible for the filter string to be referenced after its end. With the filter:

 # echo '>' > /sys/kernel/debug/events/ext4/ext4_truncate_exit/filter

The filter_parse() function can call infix_get_op() which calls infix_advance() that updates the infix filter pointers for the cnt and tail without checking if the filter is already at the end, which will put the cnt to zero and the tail beyond the end. The loop then calls infix_next() that has

	ps->infix.cnt--;
	return ps->infix.string[ps->infix.tail++];

The cnt will now be below zero, and the tail that is returned is already passed the end of the filter string. So far the allocation of the filter string usually has some buffer that is zeroed out, but if the filter string is of the exact size of the allocated buffer there's no guarantee that the charater after the nul terminating character will be zero.

Luckily, only root can write to the filter.

---
 kernel/trace/trace_events_filter.c |    6 ++++++
 1 file changed, 6 insertions(+)

@@ -1086,6 +1086,9 @@ static void parse_init(struct filter_par
 
 static char infix_next(struct filter_parse_state *ps)
 {
+	if (!ps->infix.cnt)
+		return 0;
+
 	ps->infix.cnt--;
 
 	return ps->infix.string[ps->infix.tail++];

@@ -1101,6 +1104,9 @@ static char infix_peek(struct filter_par
 
 static void infix_advance(struct filter_parse_state *ps)
 {
+	if (!ps->infix.cnt)
+		return;
+
 	ps->infix.cnt--;
 	ps->infix.tail++;
 }

Patches currently in stable-queue which might be from [email protected] are

queue-3.14/tracing-have-branch-tracer-use-recursive-field-of-task-struct.patch queue-3.14/tracing-filter-do-not-allow-infix-to-exceed-end-of-string.patch queue-3.14/tracing-filter-do-not-warn-on-operand-count-going-below-zero.patch