perf tools: Fix out-of-bound access to struct perf_session

If filename is NULL there is an out-of-bound access to struct
perf_session if it would be used with perf_session__open(). Shouldn't
actually happen in current implementation as filename is always !NULL.
Fixing this by always null-terminating filename.

Cc: Frederic Weisbecker <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Stephane Eranian <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Robert Richter <[e-mail]>
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/util/session.c

···
 				       bool force, bool repipe,
 				       struct perf_tool *tool)
 {
-	size_t len = filename ? strlen(filename) + 1 : 0;
+	size_t len = filename ? strlen(filename) : 0;
 	struct perf_session *self = zalloc(sizeof(*self) + len);
 
 	if (self == NULL)

tools/perf/util/session.h

···
 	int			cwdlen;
 	char			*cwd;
 	struct ordered_samples	ordered_samples;
-	char			filename[0];
+	char			filename[1];
 };
 
 struct perf_tool;