libselinux: store_stem(): do not free possible non-heap object

GCC 11 complains:

In file included from label_file.c:24:
In function ‘store_stem’,
    inlined from ‘load_mmap’ at label_file.c:277:12,
    inlined from ‘process_file’ at label_file.c:551:5:
label_file.h:289:25: error: ‘free’ called on pointer ‘*mmap_area.next_addr’ with nonzero offset 4 [-Werror=free-nonheap-object]
  289 |                         free(buf);
      |                         ^~~~~~~~~

Free the pointer on failure at the caller instead of inside `store_stem()`.

Signed-off-by: Christian Göttsche <[email protected]>

libselinux/src/label_file.h

@@ -286,7 +286,6 @@ static inline int store_stem(struct saved_data *data, char *buf, int stem_len)
 		tmp_arr = realloc(data->stem_arr,
 				  sizeof(*tmp_arr) * alloc_stems);
 		if (!tmp_arr) {
-			free(buf);
 			return -1;
 		}
 		data->alloc_stems = alloc_stems;
@@ -308,6 +307,7 @@ static inline int find_stem_from_spec(struct saved_data *data, const char *buf)
 	int stem_len = get_stem_from_spec(buf);
 	int stemid;
 	char *stem;
+	int r;
 
 	if (!stem_len)
 		return -1;
@@ -321,7 +321,11 @@ static inline int find_stem_from_spec(struct saved_data *data, const char *buf)
 	if (!stem)
 		return -1;
 
-	return store_stem(data, stem, stem_len);
+	r = store_stem(data, stem, stem_len);
+	if (r < 0)
+		free(stem);
+
+	return r;
 }
 
 /* This will always check for buffer over-runs and either read the next entry