[PATCH 6/6] ovl: fix corner case of non-constant st_dev;st_ino

Amir Goldstein
2019-11-17T15:44:07Z

On non-samefs overlay without xino, non pure upper inodes should use a
pseudo_dev assigned to each unique lower fs, but if lower layer is on
the same fs and upper layer, it has no pseudo_dev assigned.

In this overlay layers setup:
- 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
st_dev;st_ino values of the real lower inode before copy up and the
st_dev;st_ino values of the real upper inode after copy up.

Fix this inconsitency by assigning a unique pseudo_dev also for upper fs,
that will be used as st_dev value along with the lower inode st_dev for
overlay inodes in the case above.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---
fs/overlayfs/inode.c | 13 +++----------
fs/overlayfs/super.c | 15 ++++++++++-----
2 files changed, 13 insertions(+), 15 deletions(-)

diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index 9e894f5e19b4..00c4e9c17492 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -125,9 +125,8 @@ static int ovl_map_dev_ino(struct dentry *dentry, struct kstat *stat, int fsid)
/*
* For non-samefs setup, if we cannot map all layers st_ino
* to a unified address space, we need to make sure that st_dev
- * is unique per lower fs. Layers that are on the same fs as
- * upper layer use real upper st_dev and other lower layers use
- * the unique anonymous bdev assigned to the lower fs.
+ * is unique per underlying fs, so we use the unique anonymous
+ * bdev assigned to the underlying fs.
*/
stat->dev = OVL_FS(dentry->d_sb)->fs[fsid].pseudo_dev;
}
@@ -195,13 +194,7 @@ 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))) {
- /*
- * Cannot use origin st_dev;st_ino because
- * origin inode content may differ from overlay
- * inode content.
- */
- if (samefs || fsid)
- stat->ino = lowerstat.ino;
+ stat->ino = lowerstat.ino;
} else {
fsid = 0;
}
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index e80f79bb8a4e..9270e059eb9b 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -230,8 +230,7 @@ static void ovl_free_fs(struct ovl_fs *ofs)
}
kfree(ofs->layers);
if (ofs->fs) {
- /* fs[0].pseudo_dev is either null or real upper st_dev */
- for (i = 1; i <= ofs->maxfsid; i++)
+ for (i = 0; i <= ofs->maxfsid; i++)
free_anon_bdev(ofs->fs[i].pseudo_dev);
kfree(ofs->fs);
}
@@ -1335,13 +1334,19 @@ static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
ofs->layers[0].fsid = 0;

/*
- * All lower layers that share the same fs as upper layer, use the real
- * upper st_dev.
+ * All lower layers that share the same fs as upper layer, use the same
+ * pseudo_dev as upper layer. Allocate fs[0].pseudo_dev even for lower
+ * only overlay to simplify ovl_fs_free().
* is_lower will be set if upper fs is shared with a lower layer.
*/
+ err = get_anon_bdev(&ofs->fs[0].pseudo_dev);
+ if (err) {
+ pr_err("overlayfs: failed to get anonymous bdev for upper fs\n");
+ goto out;
+ }
+
if (ofs->upper_mnt) {
ofs->fs[0].sb = ofs->upper_mnt->mnt_sb;
- ofs->fs[0].pseudo_dev = ofs->upper_mnt->mnt_sb->s_dev;
ofs->fs[0].is_lower = false;
}

--
2.17.1