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, 4 insertions, 12 deletions

diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index 60f7b8f092f2..79e8994e3bc1 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -121,13 +121,12 @@ static int ovl_map_dev_ino(struct dentry *dentry, struct kstat *stat, int fsid)
 		 */
 		stat->dev = dentry->d_sb->s_dev;
 		stat->ino = dentry->d_inode->i_ino;
-	} else if (fsid) {
+	} else {
 		/*
 		 * 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. Upper layer uses real st_dev and
-		 * 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;
 	}
@@ -143,7 +142,6 @@ int ovl_getattr(const struct path *path, struct kstat *stat,
 	struct path realpath;
 	const struct cred *old_cred;
 	bool is_dir = S_ISDIR(dentry->d_inode->i_mode);
-	bool samefs = ovl_same_fs(dentry->d_sb);
 	int fsid = 0;
 	int err;
 	bool metacopy_blocks = false;
@@ -198,13 +196,7 @@ int ovl_getattr(const struct path *path, struct kstat *stat,
 			    (!ovl_verify_lower(dentry->d_sb) &&
 			     (is_dir || lowerstat.nlink == 1))) {
 				fsid = ovl_layer_lower(dentry)->fsid;
-				/*
-				 * 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;
 			}
 
 			/*