[PATCH userspace 1/2] libselinux: fix invalid free in store_stem()/load_mmap()

[Ondrej Mosnacek <omosnace@xxxxxxxxxx>]

Building libselinux with GCC 11.1.1 produces the following warning:
```
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);
      |                         ^~~~~~~~~
```

Indeed, in this case the pointer shouldn't be freed as it comes from
mmap. Fix this by adding a from_mmap parameter to store_stem() instead
of overriding the saved_data::from_mmap value in load_mmap().

Signed-off-by: Ondrej Mosnacek <omosnace@xxxxxxxxxx>
---
 libselinux/src/label_file.c |  3 +--
 libselinux/src/label_file.h | 12 +++++++-----
 2 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/libselinux/src/label_file.c b/libselinux/src/label_file.c
index cfce23e0..199ae66b 100644
--- a/libselinux/src/label_file.c
+++ b/libselinux/src/label_file.c
@@ -274,12 +274,11 @@ end_arch_check:
 		/* store the mapping between old and new */
 		newid = find_stem(data, buf, stem_len);
 		if (newid < 0) {
-			newid = store_stem(data, buf, stem_len);
+			newid = store_stem(data, buf, stem_len, true);
 			if (newid < 0) {
 				rc = newid;
 				goto out;
 			}
-			data->stem_arr[newid].from_mmap = 1;
 		}
 		stem_map[i] = newid;
 	}
diff --git a/libselinux/src/label_file.h b/libselinux/src/label_file.h
index baed3341..66e5721f 100644
--- a/libselinux/src/label_file.h
+++ b/libselinux/src/label_file.h
@@ -62,7 +62,7 @@ struct spec {
 struct stem {
 	char *buf;
 	int len;
-	char from_mmap;
+	bool from_mmap;
 };
 
 /* Where we map the file in during selabel_open() */
@@ -276,7 +276,8 @@ static inline int find_stem(struct saved_data *data, const char *buf,
 }
 
 /* returns the index of the new stored object */
-static inline int store_stem(struct saved_data *data, char *buf, int stem_len)
+static inline int store_stem(struct saved_data *data, char *buf, int stem_len,
+			     bool from_mmap)
 {
 	int num = data->num_stems;
 
@@ -286,7 +287,8 @@ 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);
+			if (!from_mmap)
+				free(buf);
 			return -1;
 		}
 		data->alloc_stems = alloc_stems;
@@ -294,7 +296,7 @@ static inline int store_stem(struct saved_data *data, char *buf, int stem_len)
 	}
 	data->stem_arr[num].len = stem_len;
 	data->stem_arr[num].buf = buf;
-	data->stem_arr[num].from_mmap = 0;
+	data->stem_arr[num].from_mmap = from_mmap;
 	data->num_stems++;
 
 	return num;
@@ -321,7 +323,7 @@ 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);
+	return store_stem(data, stem, stem_len, false);
 }
 
 /* This will always check for buffer over-runs and either read the next entry
-- 
2.31.1