From: Christian Brauner brauner@kernel.org
[ Upstream commit f723edb8a532cd26e1ff0a2b271d73762d48f762 ]
Porting overlayfs to the new amount api I started experiencing random crashes that couldn't be explained easily. So after much debugging and reasoning it became clear that struct ovl_entry requires the point to struct vfsmount to be the first member and of type struct vfsmount.
During the port I added a new member at the beginning of struct ovl_entry which broke all over the place in the form of random crashes and cache corruptions. While there's a comment in ovl_free_fs() to the effect of "Hack! Reuse ofs->layers as a vfsmount array before freeing it" there's no such comment on struct ovl_entry which makes this easy to trip over.
Add a comment and two static asserts for both the offset and the type of pointer in struct ovl_entry.
Signed-off-by: Christian Brauner brauner@kernel.org Signed-off-by: Amir Goldstein amir73il@gmail.com Signed-off-by: Sasha Levin sashal@kernel.org --- fs/overlayfs/ovl_entry.h | 9 +++++++++ 1 file changed, 9 insertions(+)
diff --git a/fs/overlayfs/ovl_entry.h b/fs/overlayfs/ovl_entry.h index fd11fe6d6d45f..6b9f7917fc1bb 100644 --- a/fs/overlayfs/ovl_entry.h +++ b/fs/overlayfs/ovl_entry.h @@ -32,6 +32,7 @@ struct ovl_sb { };
struct ovl_layer { + /* ovl_free_fs() relies on @mnt being the first member! */ struct vfsmount *mnt; /* Trap in ovl inode cache */ struct inode *trap; @@ -42,6 +43,14 @@ struct ovl_layer { int fsid; };
+/* + * ovl_free_fs() relies on @mnt being the first member when unmounting + * the private mounts created for each layer. Let's check both the + * offset and type. + */ +static_assert(offsetof(struct ovl_layer, mnt) == 0); +static_assert(__same_type(typeof_member(struct ovl_layer, mnt), struct vfsmount *)); + struct ovl_path { const struct ovl_layer *layer; struct dentry *dentry;