Merge branch 'overlayfs-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/vfs

Pull overlayfs fixes from Miklos Szeredi:
 "Fix a regression in 4.14 and one in 4.13. The latter is a case when
  Docker is doing something it really shouldn't and gets away with it.
  We now print a warning instead of erroring out.

  There are also fixes to several error paths"

* 'overlayfs-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/vfs:
  ovl: fix regression caused by exclusive upper/work dir protection
  ovl: fix missing unlock_rename() in ovl_do_copy_up()
  ovl: fix dentry leak in ovl_indexdir_cleanup()
  ovl: fix dput() of ERR_PTR in ovl_cleanup_index()
  ovl: fix error value printed in ovl_lookup_index()
  ovl: fix may_write_real() for overlayfs directories

Documentation/filesystems/overlayfs.txt

@@ -210,8 +210,11 @@ path as another overlay mount and it may use a lower layer path that is
 beneath or above the path of another overlay lower layer path.
 
 Using an upper layer path and/or a workdir path that are already used by
-another overlay mount is not allowed and will fail with EBUSY.  Using
+another overlay mount is not allowed and may fail with EBUSY.  Using
 partially overlapping paths is not allowed but will not fail with EBUSY.
+If files are accessed from two overlayfs mounts which share or overlap the
+upper layer and/or workdir path the behavior of the overlay is undefined,
+though it will not result in a crash or deadlock.
 
 Mounting an overlay using an upper layer path, where the upper layer path
 was previously used by another mounted overlay in combination with a

fs/namespace.c

@@ -468,7 +468,9 @@ static inline int may_write_real(struct file *file)
 
 	/* File refers to upper, writable layer? */
 	upperdentry = d_real(dentry, NULL, 0, D_REAL_UPPER);
-	if (upperdentry && file_inode(file) == d_inode(upperdentry))
+	if (upperdentry &&
+	    (file_inode(file) == d_inode(upperdentry) ||
+	     file_inode(file) == d_inode(dentry)))
 		return 0;
 
 	/* Lower layer: can't write to real file, sorry... */

fs/overlayfs/copy_up.c

@@ -561,10 +561,8 @@ static int ovl_do_copy_up(struct ovl_copy_up_ctx *c)
 		c->tmpfile = true;
 		err = ovl_copy_up_locked(c);
 	} else {
-		err = -EIO;
-		if (lock_rename(c->workdir, c->destdir) != NULL) {
-			pr_err("overlayfs: failed to lock workdir+upperdir\n");
-		} else {
+		err = ovl_lock_rename_workdir(c->workdir, c->destdir);
+		if (!err) {
 			err = ovl_copy_up_locked(c);
 			unlock_rename(c->workdir, c->destdir);
 		}

fs/overlayfs/dir.c

@@ -216,26 +216,6 @@ static int ovl_create_upper(struct dentry *dentry, struct inode *inode,
 	return err;
 }
 
-static int ovl_lock_rename_workdir(struct dentry *workdir,
-				   struct dentry *upperdir)
-{
-	/* Workdir should not be the same as upperdir */
-	if (workdir == upperdir)
-		goto err;
-
-	/* Workdir should not be subdir of upperdir and vice versa */
-	if (lock_rename(workdir, upperdir) != NULL)
-		goto err_unlock;
-
-	return 0;
-
-err_unlock:
-	unlock_rename(workdir, upperdir);
-err:
-	pr_err("overlayfs: failed to lock workdir+upperdir\n");
-	return -EIO;
-}
-
 static struct dentry *ovl_clear_empty(struct dentry *dentry,
 				      struct list_head *list)
 {

fs/overlayfs/namei.c

@@ -506,6 +506,7 @@ static struct dentry *ovl_lookup_index(struct dentry *dentry,
 
 	index = lookup_one_len_unlocked(name.name, ofs->indexdir, name.len);
 	if (IS_ERR(index)) {
+		err = PTR_ERR(index);
 		pr_warn_ratelimited("overlayfs: failed inode index lookup (ino=%lu, key=%*s, err=%i);\n"
 				    "overlayfs: mount with '-o index=off' to disable inodes index.\n",
 				    d_inode(origin)->i_ino, name.len, name.name,

fs/overlayfs/overlayfs.h

@@ -235,6 +235,7 @@ bool ovl_inuse_trylock(struct dentry *dentry);
 void ovl_inuse_unlock(struct dentry *dentry);
 int ovl_nlink_start(struct dentry *dentry, bool *locked);
 void ovl_nlink_end(struct dentry *dentry, bool locked);
+int ovl_lock_rename_workdir(struct dentry *workdir, struct dentry *upperdir);
 
 static inline bool ovl_is_impuredir(struct dentry *dentry)
 {

fs/overlayfs/ovl_entry.h

@@ -37,6 +37,9 @@ struct ovl_fs {
 	bool noxattr;
 	/* sb common to all layers */
 	struct super_block *same_sb;
+	/* Did we take the inuse lock? */
+	bool upperdir_locked;
+	bool workdir_locked;
 };
 
 /* private information held for every overlayfs dentry */

fs/overlayfs/readdir.c

@@ -988,6 +988,7 @@ int ovl_indexdir_cleanup(struct dentry *dentry, struct vfsmount *mnt,
 			 struct path *lowerstack, unsigned int numlower)
 {
 	int err;
+	struct dentry *index = NULL;
 	struct inode *dir = dentry->d_inode;
 	struct path path = { .mnt = mnt, .dentry = dentry };
 	LIST_HEAD(list);
@@ -1007,8 +1008,6 @@ int ovl_indexdir_cleanup(struct dentry *dentry, struct vfsmount *mnt,
 
 	inode_lock_nested(dir, I_MUTEX_PARENT);
 	list_for_each_entry(p, &list, l_node) {
-		struct dentry *index;
-
 		if (p->name[0] == '.') {
 			if (p->len == 1)
 				continue;
@@ -1018,6 +1017,7 @@ int ovl_indexdir_cleanup(struct dentry *dentry, struct vfsmount *mnt,
 		index = lookup_one_len(p->name, dentry, p->len);
 		if (IS_ERR(index)) {
 			err = PTR_ERR(index);
+			index = NULL;
 			break;
 		}
 		err = ovl_verify_index(index, lowerstack, numlower);
@@ -1029,7 +1029,9 @@ int ovl_indexdir_cleanup(struct dentry *dentry, struct vfsmount *mnt,
 				break;
 		}
 		dput(index);
+		index = NULL;
 	}
+	dput(index);
 	inode_unlock(dir);
 out:
 	ovl_cache_free(&list);

fs/overlayfs/super.c

@@ -211,9 +211,10 @@ static void ovl_put_super(struct super_block *sb)
 
 	dput(ufs->indexdir);
 	dput(ufs->workdir);
+	if (ufs->workdir_locked)
 		ovl_inuse_unlock(ufs->workbasedir);
 	dput(ufs->workbasedir);
-	if (ufs->upper_mnt)
+	if (ufs->upper_mnt && ufs->upperdir_locked)
 		ovl_inuse_unlock(ufs->upper_mnt->mnt_root);
 	mntput(ufs->upper_mnt);
 	for (i = 0; i < ufs->numlower; i++)
@@ -881,9 +882,13 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 			goto out_put_upperpath;
 
 		err = -EBUSY;
-		if (!ovl_inuse_trylock(upperpath.dentry)) {
-			pr_err("overlayfs: upperdir is in-use by another mount\n");
+		if (ovl_inuse_trylock(upperpath.dentry)) {
+			ufs->upperdir_locked = true;
+		} else if (ufs->config.index) {
+			pr_err("overlayfs: upperdir is in-use by another mount, mount with '-o index=off' to override exclusive upperdir protection.\n");
 			goto out_put_upperpath;
+		} else {
+			pr_warn("overlayfs: upperdir is in-use by another mount, accessing files from both mounts will result in undefined behavior.\n");
 		}
 
 		err = ovl_mount_dir(ufs->config.workdir, &workpath);
@@ -901,9 +906,13 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 		}
 
 		err = -EBUSY;
-		if (!ovl_inuse_trylock(workpath.dentry)) {
-			pr_err("overlayfs: workdir is in-use by another mount\n");
+		if (ovl_inuse_trylock(workpath.dentry)) {
+			ufs->workdir_locked = true;
+		} else if (ufs->config.index) {
+			pr_err("overlayfs: workdir is in-use by another mount, mount with '-o index=off' to override exclusive workdir protection.\n");
 			goto out_put_workpath;
+		} else {
+			pr_warn("overlayfs: workdir is in-use by another mount, accessing files from both mounts will result in undefined behavior.\n");
 		}
 
 		ufs->workbasedir = workpath.dentry;
@@ -1156,10 +1165,12 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 out_free_lowertmp:
 	kfree(lowertmp);
 out_unlock_workdentry:
+	if (ufs->workdir_locked)
 		ovl_inuse_unlock(workpath.dentry);
 out_put_workpath:
 	path_put(&workpath);
 out_unlock_upperdentry:
+	if (ufs->upperdir_locked)
 		ovl_inuse_unlock(upperpath.dentry);
 out_put_upperpath:
 	path_put(&upperpath);

fs/overlayfs/util.c

@@ -430,7 +430,7 @@ void ovl_inuse_unlock(struct dentry *dentry)
 	}
 }
 
-/* Called must hold OVL_I(inode)->oi_lock */
+/* Caller must hold OVL_I(inode)->lock */
 static void ovl_cleanup_index(struct dentry *dentry)
 {
 	struct inode *dir = ovl_indexdir(dentry->d_sb)->d_inode;
@@ -469,6 +469,9 @@ static void ovl_cleanup_index(struct dentry *dentry)
 	err = PTR_ERR(index);
 	if (!IS_ERR(index))
 		err = ovl_cleanup(dir, index);
+	else
+		index = NULL;
+
 	inode_unlock(dir);
 	if (err)
 		goto fail;
@@ -557,3 +560,22 @@ void ovl_nlink_end(struct dentry *dentry, bool locked)
 		mutex_unlock(&OVL_I(d_inode(dentry))->lock);
 	}
 }
+
+int ovl_lock_rename_workdir(struct dentry *workdir, struct dentry *upperdir)
+{
+	/* Workdir should not be the same as upperdir */
+	if (workdir == upperdir)
+		goto err;
+
+	/* Workdir should not be subdir of upperdir and vice versa */
+	if (lock_rename(workdir, upperdir) != NULL)
+		goto err_unlock;
+
+	return 0;
+
+err_unlock:
+	unlock_rename(workdir, upperdir);
+err:
+	pr_err("overlayfs: failed to lock workdir+upperdir\n");
+	return -EIO;
+}