[3.16.y-ckt stable] Patch "tracing/filter: Do not allow infix to exceed end of string" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

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

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt15.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From f7ae4936f3129d243f8a64c2701c8132024ecaf3 Mon Sep 17 00:00:00 2001
From: "Steven Rostedt (Red Hat)" <rostedt at goodmis.org>
Date: Thu, 25 Jun 2015 18:10:09 -0400
Subject: tracing/filter: Do not allow infix to exceed end of string

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.

Signed-off-by: Steven Rostedt <rostedt at goodmis.org>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 kernel/trace/trace_events_filter.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index 61959fa704ed..7b244d004d68 100644
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -1086,6 +1086,9 @@ static void parse_init(struct filter_parse_state *ps,

 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_parse_state *ps)

 static void infix_advance(struct filter_parse_state *ps)
 {
+	if (!ps->infix.cnt)
+		return;
+
 	ps->infix.cnt--;
 	ps->infix.tail++;
 }