On non-samefs overlay without xino, non pure upper inodes should use a
pseudo_dev assigned to each unique lower fs and pure upper inodes use
the real upper st_dev.
It is fine for an overlay pure upper inode to use the same st_dev;st_ino
values as the real upper inode, because the content of those two
different filesystem objects is always the same.
In this case, however:
- two filesystems, A and B
- upper layer is on A
- lower layer 1 is also on A
- lower layer 2 is on B
Non pure upper overlay inode, whose origin is in layer 1 will have the
same st_dev;st_ino values as the real lower inode. This may result with
a false positive results of 'diff' between the real lower and copied up
overlay inode.
Fix this by using the upper st_dev;st_ino values in this case.
This breaks the property of constant st_dev;st_ino across copy up
of this case. This breakage will be fixed by a later patch.
Fixes: 5148626b806a ("ovl: allocate anon bdev per unique lower fs")
Cc: stable@xxxxxxxxxxxxxxx # v4.17+
Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
---
fs/overlayfs/inode.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index bc14781886bf..b045cf1826fc 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -200,8 +200,14 @@ int ovl_getattr(const struct path *path, struct kstat *stat,
if (ovl_test_flag(OVL_INDEX, d_inode(dentry)) ||
(!ovl_verify_lower(dentry->d_sb) &&
(is_dir || lowerstat.nlink == 1))) {
- stat->ino = lowerstat.ino;
lower_layer = ovl_layer_lower(dentry);
+ /*
+ * Cannot use origin st_dev;st_ino because
+ * origin inode content may differ from overlay
+ * inode content.
+ */
+ if (samefs || lower_layer->fsid)
+ stat->ino = lowerstat.ino;
}
/*
--
2.17.1
