[PATCH libnftnl 1/7] include: str_array.h: avoid oob read

[Florian Westphal <fw@strlen.de>]

LLM says:
The increment expression unconditionally dereferences `array[len]` *before*
the loop condition can stop it. This is UB on every call regardless of `len > 0`.
If `array == NULL` and `len == 0`, the *init* expression also segfaults.

Add extra guards.

Signed-off-by: Florian Westphal <fw@strlen.de>
---
 include/str_array.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/include/str_array.h b/include/str_array.h
index 98c9b4f3e6d1..cef71cf2ca63 100644
--- a/include/str_array.h
+++ b/include/str_array.h
@@ -14,9 +14,9 @@ void nftnl_str_array_clear(struct nftnl_str_array *sa);
 int nftnl_str_array_set(struct nftnl_str_array *sa, const char * const *array);
 int nftnl_parse_devs(struct nftnl_str_array *sa, const struct nlattr *nest);
 
-#define nftnl_str_array_foreach(ptr, sa, idx)	\
-	for (idx = 0, ptr = (sa)->array[idx];	\
-	     idx < (sa)->len;			\
-	     ptr = (sa)->array[++idx])
+#define nftnl_str_array_foreach(ptr, sa, idx)			\
+	for (idx = 0, ptr = (sa)->len ? (sa)->array[0] : NULL;	\
+	     idx < (sa)->len; idx++,				\
+	     ptr = (idx < (sa)->len) ? (sa)->array[idx] : NULL)
 
 #endif /* LIBNFTNL_STR_ARRAY_H */
-- 
2.55.0