[GIT PULL] tracing: Fix regex_match_front() to not over compare the test string

[Steven Rostedt]

Linus,

Working on some new updates to trace filtering, I noticed that the
regex_match_front() test was updated to be limited to the size
of the pattern instead of the full test string. But as the test string
is not guaranteed to be nul terminated, it still needs to consider
the size of the test string.


Please pull the latest trace-v4.17-rc4 tree, which can be found at:


  git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git
trace-v4.17-rc4

Tag SHA1: cb82e07247fa5f1a91940a2928fb260256727a14
Head SHA1: dc432c3d7f9bceb3de6f5b44fb9c657c9810ed6d


Steven Rostedt (VMware) (1):
      tracing: Fix regex_match_front() to not over compare the test string

----
 kernel/trace/trace_events_filter.c | 3 +++
 1 file changed, 3 insertions(+)
---------------------------
commit dc432c3d7f9bceb3de6f5b44fb9c657c9810ed6d
Author: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
Date:   Wed May 9 11:59:32 2018 -0400

    tracing: Fix regex_match_front() to not over compare the test string
    
    The regex match function regex_match_front() in the tracing filter logic,
    was fixed to test just the pattern length from testing the entire test
    string. That is, it went from strncmp(str, r->pattern, len) to
    strcmp(str, r->pattern, r->len).
    
    The issue is that str is not guaranteed to be nul terminated, and if r->len
    is greater than the length of str, it can access more memory than is
    allocated.
    
    The solution is to add a simple test if (len < r->len) return 0.
    
    Cc: stable@xxxxxxxxxxxxxxx
    Fixes: 285caad415f45 ("tracing/filters: Fix MATCH_FRONT_ONLY filter matching")
    Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>

diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index 1f951b3df60c..7d306b74230f 100644
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -762,6 +762,9 @@ static int regex_match_full(char *str, struct regex *r, int len)
 
 static int regex_match_front(char *str, struct regex *r, int len)
 {
+	if (len < r->len)
+		return 0;
+
 	if (strncmp(str, r->pattern, r->len) == 0)
 		return 1;
 	return 0;