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ovl: check type and offset of struct vfsmount in ovl_entry
[ 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>
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@ -30,6 +30,7 @@ struct ovl_sb {
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};
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struct ovl_layer {
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/* ovl_free_fs() relies on @mnt being the first member! */
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struct vfsmount *mnt;
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/* Trap in ovl inode cache */
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struct inode *trap;
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@ -40,6 +41,14 @@ struct ovl_layer {
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int fsid;
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};
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/*
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* ovl_free_fs() relies on @mnt being the first member when unmounting
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* the private mounts created for each layer. Let's check both the
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* offset and type.
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*/
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static_assert(offsetof(struct ovl_layer, mnt) == 0);
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static_assert(__same_type(typeof_member(struct ovl_layer, mnt), struct vfsmount *));
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struct ovl_path {
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const struct ovl_layer *layer;
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struct dentry *dentry;
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