ovl: fix corner case of non-constant st_dev;st_ino

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>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

1 files changed, 10 insertions, 5 deletions

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 7cf543608b9f..dcdcb4e3003a 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -229,8 +229,7 @@ static void ovl_free_fs(struct ovl_fs *ofs)
 		mntput(ofs->layers[i].mnt);
 	}
 	kfree(ofs->layers);
-	/* fs[0].pseudo_dev is either null or real upper st_dev */
-	for (i = 1; i < ofs->numfs; i++)
+	for (i = 0; i < ofs->numfs; i++)
 		free_anon_bdev(ofs->fs[i].pseudo_dev);
 	kfree(ofs->fs);
 
@@ -1341,13 +1340,19 @@ static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
 	ofs->numlayer = 1;
 
 	/*
-	 * 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("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;
 	}