[PATCH libnftnl 6/7] src: utils: keep old name if strndup fails

[Florian Westphal <fw@strlen.de>]

LLM finding: flag/pointer state inconsistency on allocation failure.

In practice, strndup should never fail for any realistic scenario, however,
its clearly a bug.

Free old value after allocation succeded, not before.

nftnl_parse_str_attr has the same issue, delegate to the fixed function
instead of open-coding.

Signed-off-by: Florian Westphal <fw@strlen.de>
---
 src/utils.c | 24 +++++++++++++-----------
 1 file changed, 13 insertions(+), 11 deletions(-)

diff --git a/src/utils.c b/src/utils.c
index bbe44b4d532d..ec15f9bc8646 100644
--- a/src/utils.c
+++ b/src/utils.c
@@ -139,13 +139,15 @@ void __noreturn __abi_breakage(const char *file, int line, const char *reason)
 int nftnl_set_str_attr(const char **dptr, uint32_t *flags,
 		       uint16_t attr, const void *data, uint32_t data_len)
 {
-	if (*flags & (1 << attr))
-		xfree(*dptr);
+	char *new = strndup(data, data_len);
 
-	*dptr = strndup(data, data_len);
-	if (!*dptr)
+	if (!new)
 		return -1;
 
+	if (*flags & (1 << attr))
+		xfree(*dptr);
+
+	*dptr = new;
 	*flags |= (1 << attr);
 	return 0;
 }
@@ -196,14 +198,14 @@ char *nftnl_attr_get_ifname(const struct nlattr *attr)
 int nftnl_parse_str_attr(const struct nlattr *tb, int attr,
 			 const char **field, uint32_t *flags)
 {
+	const char *s;
+	uint32_t len;
+
 	if (!tb)
 		return 0;
 
-	if (*flags & (1 << attr))
-		xfree(*field);
-	*field = strdup(mnl_attr_get_str(tb));
-	if (!*field)
-		return -1;
-	*flags |= (1 << attr);
-	return 0;
+	len = mnl_attr_get_payload_len(tb);
+	s = mnl_attr_get_str(tb);
+
+	return nftnl_set_str_attr(field, flags, attr, s, len);
 }
-- 
2.55.0