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ovl: verify stored origin fh matches lower dir 

When the NFS export feature is enabled, overlayfs implicitly enables the
feature "verify_lower". When the "verify_lower" feature is enabled, a
directory inode found in lower layer by name or by redirect_dir is
verified against the file handle of the copy up origin that is stored in
the upper layer.

This introduces a change of behavior for the case of lower layer
modification while overlay is offline. A lower directory created or
moved offline under an exisitng upper directory, will not be merged with
that upper directory.

The NFS export feature should not be used after copying layers, because
the new lower directory inodes would fail verification and won't be
merged with upper directories.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
This commit is contained in:
Amir Goldstein 2018-01-10 22:29:38 +02:00 committed by Miklos Szeredi
parent f168f1098d
commit 37b12916c0
1 changed files with 12 additions and 0 deletions
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12
fs/overlayfs/namei.c
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@ -737,6 +737,18 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
}
}
/*
* When "verify_lower" feature is enabled, do not merge with a
* lower dir that does not match a stored origin xattr.
*/
if (upperdentry && !ctr && ovl_verify_lower(dentry->d_sb)) {
err = ovl_verify_origin(upperdentry, this, false);
if (err) {
dput(this);
break;
}
}
stack[ctr].dentry = this;
stack[ctr].layer = lower.layer;
ctr++;