In ovl_fill_super(), there is an if statement on line 1607 to check
whether ofs->upper_mnt is NULL:
if (!ofs->upper_mnt)
When ofs->upper_mnt is NULL and d_make_root() on line 1654 fails,
ovl_free_fs() on line 1683 is executed.
In ovl_free_fs(), ofs->upper_mnt is used on line 224:
ovl_inuse_unlock(ofs->upper_mnt->mnt_root);
Thus, a possible null-pointer dereference may occur.
To fix this bug, ofs->upper_mnt is checked before being used in
ovl_free_fs().
This bug is found by a static analysis tool STCheck written by us.
Signed-off-by: Jia-Ju Bai <baijiaju1990@xxxxxxxxx>
---
fs/overlayfs/super.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index b368e2e102fa..1d7c3d280834 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -220,7 +220,7 @@ static void ovl_free_fs(struct ovl_fs *ofs)
if (ofs->workdir_locked)
ovl_inuse_unlock(ofs->workbasedir);
dput(ofs->workbasedir);
- if (ofs->upperdir_locked)
+ if (ofs->upperdir_locked && ofs->upper_mnt)
ovl_inuse_unlock(ofs->upper_mnt->mnt_root);
mntput(ofs->upper_mnt);
for (i = 0; i < ofs->numlower; i++) {
--
2.17.0
