index: verify we have enough space left when writing index entries
In our code writing index entries, we carry around a `disk_size`
representing how much memory we have in total and pass this value to
`git_encode_varint` to do bounds checks. This does not make much sense,
as at the time when passing on this variable it is already out of date.
Fix this by subtracting used memory from `disk_size` as we go along.
Furthermore, assert we've actually got enough space left to do the final
path memcpy.
diff --git a/src/index.c b/src/index.c
index 860adaf..c29e90f 100644
--- a/src/index.c
+++ b/src/index.c
@@ -2655,15 +2655,34 @@
ondisk_ext->flags_extended = htons(entry->flags_extended &
GIT_IDXENTRY_EXTENDED_FLAGS);
path = ondisk_ext->path;
- }
- else
+ disk_size -= offsetof(struct entry_long, path);
+ } else {
path = ondisk->path;
+ disk_size -= offsetof(struct entry_short, path);
+ }
if (last) {
- path += git_encode_varint((unsigned char *) path,
+ varint_len = git_encode_varint((unsigned char *) path,
disk_size, same_len);
+ assert(varint_len > 0);
+ path += varint_len;
+ disk_size -= varint_len;
+
+ /*
+ * If using path compression, we are not allowed
+ * to have additional trailing NULs.
+ */
+ assert(disk_size == path_len + 1);
+ } else {
+ /*
+ * If no path compression is used, we do have
+ * NULs as padding. As such, simply assert that
+ * we have enough space left to write the path.
+ */
+ assert(disk_size > path_len);
}
- memcpy(path, path_start, path_len);
+
+ memcpy(path, path_start, path_len + 1);
return 0;
}
