Patch "fs/cifs: make share unaccessible at root level mountable" has been added to the 4.4-stable tree

@@ -46,6 +46,9 @@
 #define CIFS_MOUNT_CIFS_BACKUPUID 0x200000 /* backup intent bit for a user */
 #define CIFS_MOUNT_CIFS_BACKUPGID 0x400000 /* backup intent bit for a group */
 #define CIFS_MOUNT_MAP_SFM_CHR	0x800000 /* SFM/MAC mapping for illegal chars */
+#define CIFS_MOUNT_USE_PREFIX_PATH 0x1000000 /* make subpath with unaccessible
+					      * root mountable
+					      */
 
 struct cifs_sb_info {
 	struct rb_root tlink_tree;

@@ -67,5 +70,6 @@ struct cifs_sb_info {
 	struct backing_dev_info bdi;
 	struct delayed_work prune_tlinks;
 	struct rcu_head rcu;
+	char *prepath;
 };
 #endif				/* _CIFS_FS_SB_H */

@@ -686,6 +686,14 @@ cifs_do_mount(struct file_system_type *f
 		goto out_cifs_sb;
 	}
 
+	if (volume_info->prepath) {
+		cifs_sb->prepath = kstrdup(volume_info->prepath, GFP_KERNEL);
+		if (cifs_sb->prepath == NULL) {
+			root = ERR_PTR(-ENOMEM);
+			goto out_cifs_sb;
+		}
+	}
+
 	cifs_setup_cifs_sb(volume_info, cifs_sb);
 
 	rc = cifs_mount(cifs_sb, volume_info);

@@ -724,7 +732,11 @@ cifs_do_mount(struct file_system_type *f
 		sb->s_flags |= MS_ACTIVE;
 	}
 
-	root = cifs_get_root(volume_info, sb);
+	if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_USE_PREFIX_PATH)
+		root = dget(sb->s_root);
+	else
+		root = cifs_get_root(volume_info, sb);
+
 	if (IS_ERR(root))
 		goto out_super;
 

67 lines not on this page · raw message

@@ -84,6 +84,7 @@ build_path_from_dentry(struct dentry *di
 	struct dentry *temp;
 	int namelen;
 	int dfsplen;
+	int pplen = 0;
 	char *full_path;
 	char dirsep;
 	struct cifs_sb_info *cifs_sb = CIFS_SB(direntry->d_sb);

@@ -95,8 +96,12 @@ build_path_from_dentry(struct dentry *di
 		dfsplen = strnlen(tcon->treeName, MAX_TREE_SIZE + 1);
 	else
 		dfsplen = 0;
+
+	if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_USE_PREFIX_PATH)
+		pplen = cifs_sb->prepath ? strlen(cifs_sb->prepath) + 1 : 0;
+
 cifs_bp_rename_retry:
-	namelen = dfsplen;
+	namelen = dfsplen + pplen;
 	seq = read_seqbegin(&rename_lock);
 	rcu_read_lock();
 	for (temp = direntry; !IS_ROOT(temp);) {

@@ -137,7 +142,7 @@ cifs_bp_rename_retry:
 		}
 	}
 	rcu_read_unlock();
-	if (namelen != dfsplen || read_seqretry(&rename_lock, seq)) {
+	if (namelen != dfsplen + pplen || read_seqretry(&rename_lock, seq)) {
 		cifs_dbg(FYI, "did not end path lookup where expected. namelen=%ddfsplen=%d\n",
 			 namelen, dfsplen);
 		/* presumably this is only possible if racing with a rename

@@ -153,6 +158,17 @@ cifs_bp_rename_retry:
 	   those safely to '/' if any are found in the middle of the prepath */
 	/* BB test paths to Windows with '/' in the midst of prepath */
 
+	if (pplen) {
+		int i;
+
+		cifs_dbg(FYI, "using cifs_sb prepath <%s>\n", cifs_sb->prepath);
+		memcpy(full_path+dfsplen+1, cifs_sb->prepath, pplen-1);
+		full_path[dfsplen] = '\\';
+		for (i = 0; i < pplen-1; i++)
+			if (full_path[dfsplen+1+i] == '/')
+				full_path[dfsplen+1+i] = CIFS_DIR_SEP(cifs_sb);
+	}
+
 	if (dfsplen) {
 		strncpy(full_path, tcon->treeName, dfsplen);
 		if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_POSIX_PATHS) {

@@ -982,10 +982,26 @@ struct inode *cifs_root_iget(struct supe
 	struct inode *inode = NULL;
 	long rc;
 	struct cifs_tcon *tcon = cifs_sb_master_tcon(cifs_sb);
+	char *path = NULL;
+	int len;
+
+	if ((cifs_sb->mnt_cifs_flags & CIFS_MOUNT_USE_PREFIX_PATH)
+	    && cifs_sb->prepath) {
+		len = strlen(cifs_sb->prepath);
+		path = kzalloc(len + 2 /* leading sep + null */, GFP_KERNEL);
+		if (path == NULL)
+			return ERR_PTR(-ENOMEM);
+		path[0] = '/';
+		memcpy(path+1, cifs_sb->prepath, len);
+	} else {
+		path = kstrdup("", GFP_KERNEL);
+		if (path == NULL)
+			return ERR_PTR(-ENOMEM);
+	}
 
 	xid = get_xid();
 	if (tcon->unix_ext) {
-		rc = cifs_get_inode_info_unix(&inode, "", sb, xid);
+		rc = cifs_get_inode_info_unix(&inode, path, sb, xid);
 		/* some servers mistakenly claim POSIX support */
 		if (rc != -EOPNOTSUPP)
 			goto iget_no_retry;

@@ -993,7 +1009,8 @@ struct inode *cifs_root_iget(struct supe
 		tcon->unix_ext = false;
 	}
 
-	rc = cifs_get_inode_info(&inode, "", NULL, sb, xid, NULL);
+	convert_delimiter(path, CIFS_DIR_SEP(cifs_sb));
+	rc = cifs_get_inode_info(&inode, path, NULL, sb, xid, NULL);
 
 iget_no_retry:
 	if (!inode) {

@@ -1022,6 +1039,7 @@ iget_no_retry:
 	}
 
 out:
+	kfree(path);
 	/* can not call macro free_xid here since in a void func
 	 * TODO: This is no longer true
 	 */