From: Akira Fujita Subject: [PATCH 3/3] mke2fs: prevent creation of unmountable ext4 with large flex_bg count Date: Wed, 11 Jun 2014 08:38:10 +0000 Message-ID: <28989C0C9F1C0A428470D967B5FCED372A7EA3@BPXM22GP.gisp.nec.co.jp> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-2022-jp" Content-Transfer-Encoding: 8BIT Cc: Ext4 Developers List To: Theodore Tso Return-path: Received: from TYO200.gate.nec.co.jp ([210.143.35.50]:43335 "EHLO tyo200.gate.nec.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751311AbaFKIn3 convert rfc822-to-8bit (ORCPT ); Wed, 11 Jun 2014 04:43:29 -0400 Received: from tyo201.gate.nec.co.jp ([10.7.69.201]) by tyo200.gate.nec.co.jp (8.13.8/8.13.4) with ESMTP id s5B8hSRU016072 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO) for ; Wed, 11 Jun 2014 17:43:28 +0900 (JST) Content-Language: ja-JP Sender: linux-ext4-owner@vger.kernel.org List-ID: In mke2fs command, if flex_bg count is too large to filesystem blocks count, unmountable ext4 which has the out of filesystem block offset is created (Case1). Moreover this large flex_bg count causes an unintentional metadata layout (bmap-imap-itable-bmap-imap-itable .. in block group) (Case2). To fix these issues and keep healthy flex_bg layout, disallow creating ext4 with obviously large flex_bg count to filesystem blocks count. Steps to reproduce: (Case1) 1. # mke2fs -t ext4 -b 4096 -O ^resize_inode -G $((2**20)) DEV 2130483 2. # mount -t ext4 DEV MP mount: wrong fs type, bad option, bad superblock on /dev/sdb4, missing codepage or helper program, or other error In some cases useful info is found in syslog - try dmesg | tail or so 3. # dumpe2fs DEV Block count: 2130483 Flex block group size: 1048576 Group 65: (Blocks 2129920-2130482) [INODE_UNINIT] Checksum 0x4cb3, unused inodes 8080 Block bitmap at 67 (bg #0 + 67), Inode bitmap at 1048643 (bg #32 + 67) Inode table at 2129979-2130483 (+59) <---- 2130483 is out of FS! 65535 free blocks, 8080 free inodes, 0 directories, 8080 unused inodes Free blocks: Free inodes: 525201-533280 (Case2) 1. # mke2fs -t ext4 -G 2147483648 DEV 3145728 2. # debugfs -R stats DEV Block count: 786432 Flex block group size: 2147483648 Group 0: block bitmap at 193, inode bitmap at 194, inode table at 195 <-- 20233 free blocks, 8181 free inodes, 2 used directories, 8181 unused inodes [Checksum 0xa597] Group 1: block bitmap at 707, inode bitmap at 708, inode table at 709 <-- 32575 free blocks, 8192 free inodes, 0 used directories, 8192 unused inodes [Inode not init, Block not init, Checksum 0x196f] Group 2: block bitmap at 1221, inode bitmap at 1222, inode table at 1223 <-- 32768 free blocks, 8192 free inodes, 0 used directories, 8192 unused inodes [Inode not init, Block not init, Checksum 0x856f] Signed-off-by: Akira Fujita --- lib/ext2fs/initialize.c | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) diff --git a/lib/ext2fs/initialize.c b/lib/ext2fs/initialize.c index 75fbf8e..34753d0 100644 --- a/lib/ext2fs/initialize.c +++ b/lib/ext2fs/initialize.c @@ -91,8 +91,10 @@ errcode_t ext2fs_initialize(const char *name, int flags, unsigned int rem; unsigned int overhead = 0; unsigned int ipg; + unsigned int flexbg_size; dgrp_t i; blk64_t free_blocks; + blk64_t flexbg_overhead; blk_t numblocks; int rsv_gdt; int csum_flag; @@ -419,6 +421,28 @@ ipg_retry: } /* + * Calculate the flex_bg related metadata blocks count. + * It includes the boot block, the super block, + * the block group descriptors, the reserved gdt blocks, + * the block bitmaps, the inode bitmaps and the inode tables. + * This is a simple check, so that the backup superblock and + * other feature related blocks are not considered. + */ + flexbg_size = 1 << fs->super->s_log_groups_per_flex; + flexbg_overhead = super->s_first_data_block + 1 + + fs->desc_blocks + super->s_reserved_gdt_blocks + + (__u64)flexbg_size * (2 + fs->inode_blocks_per_group); + + /* + * Disallow creating ext4 which breaks flex_bg metadata layout + * obviously. + */ + if (flexbg_overhead > ext2fs_blocks_count(fs->super)) { + retval = EXT2_ET_INVALID_ARGUMENT; + goto cleanup; + } + + /* * At this point we know how big the filesystem will be. So * we can do any and all allocations that depend on the block * count.