[tip:perf/core] perf header: Fix unchecked usage of strncpy()

[tip-bot for Arnaldo Carvalho de Melo]

Commit-ID:  7572588085a13d5db02bf159542189f52fdb507e
Gitweb:     https://git.kernel.org/tip/7572588085a13d5db02bf159542189f52fdb507e
Author:     Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
AuthorDate: Thu, 6 Dec 2018 11:02:57 -0300
Committer:  Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
CommitDate: Mon, 17 Dec 2018 14:59:06 -0300

perf header: Fix unchecked usage of strncpy()

The strncpy() function may leave the destination string buffer
unterminated, better use strlcpy() that we have a __weak fallback
implementation for systems without it.

This fixes this warning on an Alpine Linux Edge system with gcc 8.2:

  util/header.c: In function 'perf_event__synthesize_event_update_unit':
  util/header.c:3586:2: error: 'strncpy' output truncated before terminating nul copying as many bytes from a string as its length [-Werror=stringop-truncation]
    strncpy(ev->data, evsel->unit, size);
    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  util/header.c:3579:16: note: length computed here
    size_t size = strlen(evsel->unit);
                  ^~~~~~~~~~~~~~~~~~~

Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Fixes: a6e5281780d1 ("perf tools: Add event_update event unit type")
Link: https://lkml.kernel.org/n/tip-fiikh5nay70bv4zskw2aa858@xxxxxxxxxxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 tools/perf/util/header.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
index 4a64739c67e7..c87cfe6b7c96 100644
--- a/tools/perf/util/header.c
+++ b/tools/perf/util/header.c
@@ -3583,7 +3583,7 @@ perf_event__synthesize_event_update_unit(struct perf_tool *tool,
 	if (ev == NULL)
 		return -ENOMEM;
 
-	strncpy(ev->data, evsel->unit, size);
+	strlcpy(ev->data, evsel->unit, size + 1);
 	err = process(tool, (union perf_event *)ev, NULL, NULL);
 	free(ev);
 	return err;