ovl: no direct iteration for dir with origin xattr

If a non-merge dir in an overlay mount has an overlay.origin xattr, it
means it was once an upper merge dir, which may contain whiteouts and
then the lower dir was removed under it.

Do not iterate real dir directly in this case to avoid exposing whiteouts.

[SzM] Set OVL_WHITEOUT for all merge directories as well.

[amir] A directory that was just copied up does not have the OVL_WHITEOUTS
flag. We need to set it to fix merge dir iteration.
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/overlayfs/copy_up.c

@@ -486,6 +486,7 @@ static int ovl_copy_up_inode(struct ovl_copy_up_ctx *c, struct dentry *temp)
 static int ovl_copy_up_locked(struct ovl_copy_up_ctx *c)
 {
 	struct inode *udir = c->destdir->d_inode;
+	struct inode *inode;
 	struct dentry *newdentry = NULL;
 	struct dentry *temp = NULL;
 	int err;
@@ -508,7 +509,11 @@ static int ovl_copy_up_locked(struct ovl_copy_up_ctx *c)
 	if (err)
 		goto out_cleanup;
 
-	ovl_inode_update(d_inode(c->dentry), newdentry);
+	inode = d_inode(c->dentry);
+	ovl_inode_update(inode, newdentry);
+	if (S_ISDIR(inode->i_mode))
+		ovl_set_flag(OVL_WHITEOUTS, inode);
+
 out:
 	dput(temp);
 	return err;

fs/overlayfs/inode.c

@@ -661,6 +661,16 @@ struct inode *ovl_get_inode(struct dentry *dentry, struct dentry *upperdentry,
 	if (upperdentry && ovl_is_impuredir(upperdentry))
 		ovl_set_flag(OVL_IMPURE, inode);
 
+	/* Check for non-merge dir that may have whiteouts */
+	if (S_ISDIR(realinode->i_mode)) {
+		struct ovl_entry *oe = dentry->d_fsdata;
+
+		if (((upperdentry && lowerdentry) || oe->numlower > 1) ||
+		    ovl_check_origin_xattr(upperdentry ?: lowerdentry)) {
+			ovl_set_flag(OVL_WHITEOUTS, inode);
+		}
+	}
+
 	if (inode->i_state & I_NEW)
 		unlock_new_inode(inode);
 out:

fs/overlayfs/overlayfs.h

@@ -28,7 +28,10 @@ enum ovl_path_type {
 #define OVL_XATTR_NLINK OVL_XATTR_PREFIX "nlink"
 
 enum ovl_flag {
+	/* Pure upper dir that may contain non pure upper entries */
 	OVL_IMPURE,
+	/* Non-merge dir that may contain whiteout entries */
+	OVL_WHITEOUTS,
 	OVL_INDEX,
 };
 
@@ -223,6 +226,7 @@ bool ovl_is_whiteout(struct dentry *dentry);
 struct file *ovl_path_open(struct path *path, int flags);
 int ovl_copy_up_start(struct dentry *dentry);
 void ovl_copy_up_end(struct dentry *dentry);
+bool ovl_check_origin_xattr(struct dentry *dentry);
 bool ovl_check_dir_xattr(struct dentry *dentry, const char *name);
 int ovl_check_setxattr(struct dentry *dentry, struct dentry *upperdentry,
 		       const char *name, const void *value, size_t size,

fs/overlayfs/readdir.c

@@ -316,21 +316,37 @@ static inline int ovl_dir_read(struct path *realpath,
 	return err;
 }
 
+/*
+ * Can we iterate real dir directly?
+ *
+ * Non-merge dir may contain whiteouts from a time it was a merge upper, before
+ * lower dir was removed under it and possibly before it was rotated from upper
+ * to lower layer.
+ */
+static bool ovl_dir_is_real(struct dentry *dir)
+{
+	return !ovl_test_flag(OVL_WHITEOUTS, d_inode(dir));
+}
+
 static void ovl_dir_reset(struct file *file)
 {
 	struct ovl_dir_file *od = file->private_data;
 	struct ovl_dir_cache *cache = od->cache;
 	struct dentry *dentry = file->f_path.dentry;
-	enum ovl_path_type type = ovl_path_type(dentry);
+	bool is_real;
 
 	if (cache && ovl_dentry_version_get(dentry) != cache->version) {
 		ovl_cache_put(od, dentry);
 		od->cache = NULL;
 		od->cursor = NULL;
 	}
-	WARN_ON(!od->is_real && !OVL_TYPE_MERGE(type));
-	if (od->is_real && OVL_TYPE_MERGE(type))
+	is_real = ovl_dir_is_real(dentry);
+	if (od->is_real != is_real) {
+		/* is_real can only become false when dir is copied up */
+		if (WARN_ON(is_real))
+			return;
 		od->is_real = false;
+	}
 }
 
 static int ovl_dir_read_merged(struct dentry *dentry, struct list_head *list,
@@ -816,7 +832,7 @@ static int ovl_dir_open(struct inode *inode, struct file *file)
 		return PTR_ERR(realfile);
 	}
 	od->realfile = realfile;
-	od->is_real = !OVL_TYPE_MERGE(type);
+	od->is_real = ovl_dir_is_real(file->f_path.dentry);
 	od->is_upper = OVL_TYPE_UPPER(type);
 	file->private_data = od;
 

fs/overlayfs/super.c

@@ -1141,6 +1141,8 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 
 	root_dentry->d_fsdata = oe;
 
+	/* Root is always merge -> can have whiteouts */
+	ovl_set_flag(OVL_WHITEOUTS, d_inode(root_dentry));
 	ovl_inode_init(d_inode(root_dentry), upperpath.dentry,
 		       ovl_dentry_lower(root_dentry));
 

fs/overlayfs/util.c

@@ -329,6 +329,19 @@ void ovl_copy_up_end(struct dentry *dentry)
 	mutex_unlock(&OVL_I(d_inode(dentry))->lock);
 }
 
+bool ovl_check_origin_xattr(struct dentry *dentry)
+{
+	int res;
+
+	res = vfs_getxattr(dentry, OVL_XATTR_ORIGIN, NULL, 0);
+
+	/* Zero size value means "copied up but origin unknown" */
+	if (res >= 0)
+		return true;
+
+	return false;
+}
+
 bool ovl_check_dir_xattr(struct dentry *dentry, const char *name)
 {
 	int res;