From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752016Ab2LUKfn (ORCPT ); Fri, 21 Dec 2012 05:35:43 -0500 Received: from mail.parknet.co.jp ([210.171.160.6]:55185 "EHLO mail.parknet.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751594Ab2LUKfd (ORCPT ); Fri, 21 Dec 2012 05:35:33 -0500 From: OGAWA Hirofumi To: Namjae Jeon Cc: akpm@linux-foundation.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Namjae Jeon , Ravishankar N , Amit Sahrawat Subject: Re: [PATCH v5 7/8] fat (exportfs): rebuild directory-inode if fat_dget() fails References: <1353504311-6020-1-git-send-email-linkinjeon@gmail.com> <878v9f5ugn.fsf@devron.myhome.or.jp> <87k3sy17vk.fsf@devron.myhome.or.jp> <87txs0x45r.fsf@devron.myhome.or.jp> <87623ydnvq.fsf@devron.myhome.or.jp> <877gobn7fy.fsf@devron.myhome.or.jp> Date: Fri, 21 Dec 2012 19:35:30 +0900 In-Reply-To: (Namjae Jeon's message of "Fri, 21 Dec 2012 19:15:29 +0900") Message-ID: <87obhnlmkt.fsf@devron.myhome.or.jp> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3.50 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Namjae Jeon writes: >> Yes, we can't use fat_search_long() as is, of course. However, we can >> share the basic algorithm and code. >> >> The both are doing, >> >> 1) traverse the blocks chained by ->i_start. >> 2) get the record (dirent) from blocks. >> 3) check the detail of record >> >> The difference is only (3), right? I know, the code has many differences >> though. The actual logic are almost same. >> >> And see, e.g., fat_get_cluster() is checking several unexpected >> state. We have to care about corrupting data. It is not only >> "infinite-loop" case. And why I'm saying it is better to share code. > > Regarding unexpected conditions, > When we compare the unexpected conditions in fat_get_cluster: > We get these as conditions which can arise: > fat_end_read() returns: > 1) < 0 > 2) FAT_ENT_FREE > 3) FAT_ENT_EOF > And the last is > 4) Preventing the infinite looping of cluster chain. > > Our patch is already covering the cases: > case 1) , 2) => if (search_clus < 0 || search_clus == FAT_ENT_FREE) > about case 3) => while (search_clus != FAT_ENT_EOF); > > while for Case 4: > We can make changes like this: > > @@ -179,8 +179,9 @@ struct dentry *fat_get_parent(struct dentry *child_dir) > struct inode *parent_inode = NULL; > struct msdos_sb_info *sbi = MSDOS_SB(sb); > int parent_logstart; > - int search_clus, clus_to_match; > + int search_clus, clus_to_match, clus_count = 0; > sector_t blknr; > + const int limit = sb->s_maxbytes >> MSDOS_SB(sb)->cluster_bits; > > if (!fat_get_dotdot_entry(child_dir->d_inode, &dotdot_bh, &de)) { > parent_logstart = fat_get_start(sbi, de); > @@ -223,6 +224,14 @@ struct dentry *fat_get_parent(struct dentry *child_dir) > search_clus, clus_to_match); > if (IS_ERR(parent_inode) || parent_inode) > break; > + if (++clus_count > limit) { > + fat_fs_error_ratelimit(sb, > + "%s: detected the cluster chain loop" > + " while reading directory entries from" > + " cluster %d", __func__, search_clus); > + parent_inode = ERR_PTR(-EIO); > + break; > + } > fatent_init(&fatent); > search_clus = fat_ent_read(sb, &fatent, > search_clus); and it is copy of fat_get_cluster(), right? It would be sane as start though, it is true to increase maintain cost, and it makes more similar to fat_search_long() path. It is why I said, copy at first, and refactoring after that. -- OGAWA Hirofumi