perf probe: Fix unchecked usage of strncpy()

Commit-ID:  11435d1a1e325c6e7b0a411905235638deff742b
Gitweb:     https://git.kernel.org/tip/11435d1a1e325c6e7b0a411905235638deff742b
Author:     Arnaldo Carvalho de Melo <[email protected]>
AuthorDate: Thu, 6 Dec 2018 11:50:08 -0300
Committer:  Arnaldo Carvalho de Melo <[email protected]>
CommitDate: Thu, 6 Dec 2018 16:42:19 -0300

perf probe: 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.

In this case the 'target' buffer is coming from a list of build-ids that are expected to have a len of at most (SBUILD_ID_SIZE - 1) chars, so probably we're safe, but since we're using strncpy() here, use strlcpy() instead to provide the intended safety checking without the using the problematic strncpy() function.

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

util/probe-file.c: In function 'probe_cache__open.isra.5':
util/probe-file.c:427:3: error: 'strncpy' specified bound 41 equals destination size [-Werror=stringop-truncation]

     strncpy(sbuildid, target, SBUILD_ID_SIZE);
     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

cc1: all warnings being treated as errors

---
 tools/perf/util/probe-file.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index aac7817d9e14..0b1195cad0e5 100644
@@ -424,7 +424,7 @@ static int probe_cache__open(struct probe_cache *pcache, const char *target,
 
 	if (target && build_id_cache__cached(target)) {
 		/* This is a cached buildid */
-		strncpy(sbuildid, target, SBUILD_ID_SIZE);
+		strlcpy(sbuildid, target, SBUILD_ID_SIZE);
 		dir_name = build_id_cache__linkname(sbuildid, NULL, 0);
 		goto found;
 	}