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ovl: unbless lower st_ino of unverified origin

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On a malformed overlay, several redirected dirs can point to the same
dir on a lower layer. This presents a similar challenge as broken
hardlinks, because different objects in the overlay can return the same
st_ino/st_dev pair from stat(2).

For broken hardlinks, we do not provide constant st_ino on copy up to
avoid this inconsistency. When NFS export feature is enabled, apply
the same logic to files and directories with unverified lower origin.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
This commit is contained in:
Amir Goldstein 2017-11-21 13:55:51 +02:00 committed by Miklos Szeredi
parent 37b12916c0
commit 86eaa13046
1 changed files with 12 additions and 4 deletions
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16
fs/overlayfs/inode.c
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@ -105,12 +105,20 @@ int ovl_getattr(const struct path *path, struct kstat *stat,
* Lower hardlinks may be broken on copy up to different
* upper files, so we cannot use the lower origin st_ino
* for those different files, even for the same fs case.
*
* Similarly, several redirected dirs can point to the
* same dir on a lower layer. With the "verify_lower"
* feature, we do not use the lower origin st_ino, if
* we haven't verified that this redirect is unique.
*
* With inodes index enabled, it is safe to use st_ino
* of an indexed hardlinked origin. The index validates
* that the upper hardlink is not broken.
* of an indexed origin. The index validates that the
* upper hardlink is not broken and that a redirected
* dir is the only redirect to that origin.
*/
if (is_dir || lowerstat.nlink == 1 ||
ovl_test_flag(OVL_INDEX, d_inode(dentry)))
if (ovl_test_flag(OVL_INDEX, d_inode(dentry)) ||
(!ovl_verify_lower(dentry->d_sb) &&
(is_dir || lowerstat.nlink == 1)))
stat->ino = lowerstat.ino;
if (samefs)