[PATCH 3.16 365/366] perf thread_map: Correctly size buffer used with dirent->dt_name

[Ben Hutchings]

3.16.61-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>

commit bdf23a9a190d7ecea092fd5c4aabb7d4bd0a9980 upstream.

The size of dirent->dt_name is NAME_MAX + 1, but the size for the 'path'
buffer is hard coded at 256, which may truncate it because we also
prepend "/proc/", so that all that into account and thank gcc 7 for this
warning:

  /git/linux/tools/perf/util/thread_map.c: In function 'thread_map__new_by_uid':
  /git/linux/tools/perf/util/thread_map.c:119:39: error: '%s' directive output may be truncated writing up to 255 bytes into a region of size 250 [-Werror=format-truncation=]
     snprintf(path, sizeof(path), "/proc/%s", dirent->d_name);
                                         ^~
  In file included from /usr/include/stdio.h:939:0,
                   from /git/linux/tools/perf/util/thread_map.c:5:
  /usr/include/bits/stdio2.h:64:10: note: '__builtin___snprintf_chk' output between 7 and 262 bytes into a destination of size 256
     return __builtin___snprintf_chk (__s, __n, __USE_FORTIFY_LEVEL - 1,
            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          __bos (__s), __fmt, __va_arg_pack ());
          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx>
Cc: David Ahern <dsahern@xxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Wang Nan <wangnan0@xxxxxxxxxx>
Link: http://lkml.kernel.org/n/tip-csy0r8zrvz5efccgd4k12c82@xxxxxxxxxxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 tools/perf/util/thread_map.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/tools/perf/util/thread_map.c
+++ b/tools/perf/util/thread_map.c
@@ -63,7 +63,7 @@ struct thread_map *thread_map__new_by_ui
 {
 	DIR *proc;
 	int max_threads = 32, items, i;
-	char path[256];
+	char path[NAME_MAX + 1 + 6];
 	struct dirent *dirent, **namelist = NULL;
 	struct thread_map *threads = malloc(sizeof(*threads) +
 					    max_threads * sizeof(pid_t));