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ovl: check type and offset of struct vfsmount in ovl_entry

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[ Upstream commit f723edb8a5 ]

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>
This commit is contained in:
Christian Brauner 2023-06-13 10:13:37 +02:00 • committed by Justin Hammond
parent a534f8b484
commit 1bf8f34096
1 changed files with 9 additions and 0 deletions
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9
fs/overlayfs/ovl_entry.h
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@ -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;