perf: Fix read buffer overflow

Check whether index is within bounds before testing the element.

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Cc: a.p.zijlstra@chello.nl
Cc: Andrew Morton <akpm@linux-foundation.org>
LKML-Reference: <4A757BCF.40101@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

tools/perf/builtin-report.c

@@ -253,7 +253,7 @@ static int strcommon(const char *pathname)
 {
 	int n = 0;
 
-	while (pathname[n] == cwd[n] && n < cwdlen)
+	while (n < cwdlen && pathname[n] == cwd[n])
 		++n;
 
 	return n;