tracing: Fix regex_match_front() to not over compare the test string

commit dc432c3d7f9bceb3de6f5b44fb9c657c9810ed6d upstream.

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.

Fixes: 285caad415f45 ("tracing/filters: Fix MATCH_FRONT_ONLY filter matching")
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index ebbb24147d5150e32389e68ea82a2ffba21503cf..7b5c9a63dfdbb2bf4215813c44fab821c6c9f33e 100644 (file)
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -273,6 +273,9 @@ 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;