ovl: lookup indexed ancestor of lower dir

ovl_lookup_real() in lower layer walks back lower parents to find the
topmost indexed parent. If an indexed ancestor is found before reaching
lower layer root, ovl_lookup_real() is called recursively with upper
layer to walk back from indexed upper to the topmost connected/hashed
upper parent (or up to root).

ovl_lookup_real() in upper layer then walks forward to connect the topmost
upper overlay dir dentry and ovl_lookup_real() in lower layer continues to
walk forward to connect the decoded lower overlay dir dentry.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/overlayfs/export.c

@@ -294,6 +294,10 @@ fail:
 	goto out;
 }
 
+static struct dentry *ovl_lookup_real(struct super_block *sb,
+				      struct dentry *real,
+				      struct ovl_layer *layer);
+
 /*
  * Lookup an indexed or hashed overlay dentry by real inode.
  */
@@ -301,9 +305,16 @@ static struct dentry *ovl_lookup_real_inode(struct super_block *sb,
 					    struct dentry *real,
 					    struct ovl_layer *layer)
 {
+	struct ovl_fs *ofs = sb->s_fs_info;
+	struct ovl_layer upper_layer = { .mnt = ofs->upper_mnt };
+	struct dentry *index = NULL;
 	struct dentry *this = NULL;
 	struct inode *inode;
 
+	/*
+	 * Decoding upper dir from index is expensive, so first try to lookup
+	 * overlay dentry in inode/dcache.
+	 */
 	inode = ovl_lookup_inode(sb, real, !layer->idx);
 	if (IS_ERR(inode))
 		return ERR_CAST(inode);
@@ -312,7 +323,35 @@ static struct dentry *ovl_lookup_real_inode(struct super_block *sb,
 		iput(inode);
 	}
 
-	/* TODO: use index when looking up by origin inode */
+	/*
+	 * For decoded lower dir file handle, lookup index by origin to check
+	 * if lower dir was copied up and and/or removed.
+	 */
+	if (!this && layer->idx && ofs->indexdir && !WARN_ON(!d_is_dir(real))) {
+		index = ovl_lookup_index(ofs, NULL, real, false);
+		if (IS_ERR(index))
+			return index;
+	}
+
+	/* Get connected upper overlay dir from index */
+	if (index) {
+		struct dentry *upper = ovl_index_upper(ofs, index);
+
+		dput(index);
+		if (IS_ERR_OR_NULL(upper))
+			return upper;
+
+		/*
+		 * ovl_lookup_real() in lower layer may call recursively once to
+		 * ovl_lookup_real() in upper layer. The first level call walks
+		 * back lower parents to the topmost indexed parent. The second
+		 * recursive call walks back from indexed upper to the topmost
+		 * connected/hashed upper parent (or up to root).
+		 */
+		this = ovl_lookup_real(sb, upper, &upper_layer);
+		dput(upper);
+	}
+
 	if (!this)
 		return NULL;
 

fs/overlayfs/namei.c

@@ -661,11 +661,9 @@ struct dentry *ovl_get_index_fh(struct ovl_fs *ofs, struct ovl_fh *fh)
 	return ERR_PTR(err);
 }
 
-static struct dentry *ovl_lookup_index(struct dentry *dentry,
-				       struct dentry *upper,
-				       struct dentry *origin)
+struct dentry *ovl_lookup_index(struct ovl_fs *ofs, struct dentry *upper,
+				struct dentry *origin, bool verify)
 {
-	struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
 	struct dentry *index;
 	struct inode *inode;
 	struct qstr name;
@@ -693,6 +691,16 @@ static struct dentry *ovl_lookup_index(struct dentry *dentry,
 	inode = d_inode(index);
 	if (d_is_negative(index)) {
 		goto out_dput;
+	} else if (ovl_is_whiteout(index) && !verify) {
+		/*
+		 * When index lookup is called with !verify for decoding an
+		 * overlay file handle, a whiteout index implies that decode
+		 * should treat file handle as stale and no need to print a
+		 * warning about it.
+		 */
+		dput(index);
+		index = ERR_PTR(-ESTALE);
+		goto out;
 	} else if (ovl_dentry_weird(index) || ovl_is_whiteout(index) ||
 		   ((inode->i_mode ^ d_inode(origin)->i_mode) & S_IFMT)) {
 		/*
@@ -706,7 +714,7 @@ static struct dentry *ovl_lookup_index(struct dentry *dentry,
 				    index, d_inode(index)->i_mode & S_IFMT,
 				    d_inode(origin)->i_mode & S_IFMT);
 		goto fail;
-	} else if (is_dir) {
+	} else if (is_dir && verify) {
 		if (!upper) {
 			pr_warn_ratelimited("overlayfs: suspected uncovered redirected dir found (origin=%pd2, index=%pd2).\n",
 					    origin, index);
@@ -943,7 +951,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 
 	if (origin && ovl_indexdir(dentry->d_sb) &&
 	    (!d.is_dir || ovl_index_all(dentry->d_sb))) {
-		index = ovl_lookup_index(dentry, upperdentry, origin);
+		index = ovl_lookup_index(ofs, upperdentry, origin, true);
 		if (IS_ERR(index)) {
 			err = PTR_ERR(index);
 			index = NULL;

fs/overlayfs/overlayfs.h

@@ -274,6 +274,8 @@ struct dentry *ovl_index_upper(struct ovl_fs *ofs, struct dentry *index);
 int ovl_verify_index(struct ovl_fs *ofs, struct dentry *index);
 int ovl_get_index_name(struct dentry *origin, struct qstr *name);
 struct dentry *ovl_get_index_fh(struct ovl_fs *ofs, struct ovl_fh *fh);
+struct dentry *ovl_lookup_index(struct ovl_fs *ofs, struct dentry *upper,
+				struct dentry *origin, bool verify);
 int ovl_path_next(int idx, struct dentry *dentry, struct path *path);
 struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 			  unsigned int flags);