Commit 8f203dd4 authored Jun 13, 2023 by Christian Brauner Committed by Greg Kroah-Hartman Aug 30, 2023

ovl: check type and offset of struct vfsmount in ovl_entry



[ 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>

parent 8abed186

fs/overlayfs/ovl_entry.h

+9 −0

Original line number	Diff line number	Diff line
		@@ -27,6 +27,7 @@ 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;
		@@ -37,6 +38,14 @@ 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 {
		struct ovl_layer *layer;
		struct dentry *dentry;