[dm-devel] [PATCH 04/30] libmultipath: fix -Wstringop-overflow warning in merge_words()

[Martin Wilck]

Fixes the following warning from gcc 9:

In file included from /usr/include/string.h:494,
                 from dmparser.c:8:
In function ‘strncpy’,
    inlined from ‘merge_words’ at dmparser.c:41:2:
/usr/include/bits/string_fortified.h:106:10: warning: ‘__builtin_strncpy’
                 specified bound depends on the length of the source argument
                 [-Wstringop-overflow=]
  106 |   return __builtin___strncpy_chk (__dest, __src, __len, __bos (__dest));
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
dmparser.c: In function ‘merge_words’:
dmparser.c:41:19: note: length computed here
   41 |  strncpy(p, word, strlen(word) + 1);
      |                   ^~~~~~~~~~~~

Signed-off-by: Martin Wilck <mwilck at suse.com>
---
 libmultipath/dmparser.c | 15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/libmultipath/dmparser.c b/libmultipath/dmparser.c
index 04f675c1..a8b0b71a 100644
--- a/libmultipath/dmparser.c
+++ b/libmultipath/dmparser.c
@@ -21,24 +21,21 @@ static int
 merge_words(char **dst, char *word)
 {
 	char * p = *dst;
-	int len;
+	int len, dstlen;
 
-	len = strlen(*dst) + strlen(word) + 1;
-	*dst = REALLOC(*dst, len + 1);
+	dstlen = strlen(*dst);
+	len = dstlen + strlen(word) + 2;
+	*dst = REALLOC(*dst, len);
 
 	if (!*dst) {
 		free(p);
 		return 1;
 	}
 
-	p = *dst;
-
-	while (*p != '\0')
-		p++;
-
+	p = *dst + dstlen;
 	*p = ' ';
 	++p;
-	strncpy(p, word, strlen(word) + 1);
+	strncpy(p, word, len - dstlen - 1);
 
 	return 0;
 }
-- 
2.21.0