From: Peng Tao Subject: Re: [PATCH 2/2] ext4: fix null pointer bug in move_extent.c Date: Sun, 09 Aug 2009 01:18:32 +0800 Message-ID: <4A7DB368.1000709@gmail.com> References: <1249213404-6277-1-git-send-email-bergwolf@gmail.com> <1249213404-6277-2-git-send-email-bergwolf@gmail.com> <4A76A043.20105@rs.jp.nec.com> <6149e97b0908030620w3a4b4d9em7d8b1aa4940e837d@mail.gmail.com> <4A77F049.4050301@rs.jp.nec.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Cc: linux-ext4@vger.kernel.org, Theodore Ts'o To: Akira Fujita Return-path: Received: from wa-out-1112.google.com ([209.85.146.180]:15529 "EHLO wa-out-1112.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751236AbZHHRSi (ORCPT ); Sat, 8 Aug 2009 13:18:38 -0400 Received: by wa-out-1112.google.com with SMTP id j5so462914wah.21 for ; Sat, 08 Aug 2009 10:18:38 -0700 (PDT) In-Reply-To: <4A77F049.4050301@rs.jp.nec.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: Hi, Akira Sorry to response late. Akira Fujita wrote: > Hi Peng, > > Peng Tao wrote: >> Will there be situations where empty extents exist in the middle of an >> extent tree? Because your patch only checks NULL extents once at the >> begining. If some NULL extents are later found in the loop, the bug >> still can be triggered and we should check NULL extents in >> mext_replace_branches(). > > In the case of eh->entries is 0 in ext4_ext_find_extent(), > the extent which ext4_ext_path indicates is null. > This is happened if file blocks are not allocated yet. > But an extent tree does not have empty extents in the middle of it, I think. I'm afraid it does when the targeted extent points to an empty leaf. from fs/ext4/extents.c ext4_ext_find_extent() 681 682 /* find extent */ 683 ext4_ext_binsearch(inode, path + ppos, block); 684 /* if not an empty leaf */ 685 if (path[ppos].p_ext) 686 path[ppos].p_block = ext_pblock(path[ppos].p_ext); 687 Please correct me if I am wrong. BTW, I don't think ENOENT (translated to "No such file or directory") is a good return value , because the file is obviously out there. It just has empty extents. > > I have no idea we should handle empty extents case in EXT4_IOC_MOVE_EXTENTS, > but if yes, we should do null check at other places > not only mext_replace_branches(). > > So I add this null check to get_ext_path macro > which is used to get ext4_ext_path. > > Regards, > Akira Fujita > > Signed-off-by: Akira Fujita > --- > move_extent.c | 32 +++++++++++++++----------------- > 1 file changed, 15 insertions(+), 17 deletions(-) > --- linux-2.6.31-rc4-a/fs/ext4/move_extent.c 2009-07-23 11:32:59.000000000 +0900 > +++ linux-2.6.31-rc4-b/fs/ext4/move_extent.c 2009-08-04 15:51:04.000000000 +0900 > @@ -25,6 +25,8 @@ > if (IS_ERR(path)) { \ > ret = PTR_ERR(path); \ > path = NULL; \ > + } else if (path[ext_depth(inode)].p_ext == NULL) { \ > + ret = -ENOENT; \ > } \ > } while (0) > > @@ -284,7 +286,7 @@ mext_insert_across_blocks(handle_t *hand > > if (new_flag) { > get_ext_path(orig_path, orig_inode, eblock, err); > - if (orig_path == NULL) > + if (err) > goto out; > > if (ext4_ext_insert_extent(handle, orig_inode, > @@ -295,7 +297,7 @@ mext_insert_across_blocks(handle_t *hand > if (end_flag) { > get_ext_path(orig_path, orig_inode, > le32_to_cpu(end_ext->ee_block) - 1, err); > - if (orig_path == NULL) > + if (err) > goto out; > > if (ext4_ext_insert_extent(handle, orig_inode, > @@ -632,12 +634,12 @@ mext_replace_branches(handle_t *handle, > > /* Get the original extent for the block "orig_off" */ > get_ext_path(orig_path, orig_inode, orig_off, err); > - if (orig_path == NULL) > + if (err) > goto out; > > /* Get the donor extent for the head */ > get_ext_path(donor_path, donor_inode, donor_off, err); > - if (donor_path == NULL) > + if (err) > goto out; > depth = ext_depth(orig_inode); > oext = orig_path[depth].p_ext; > @@ -679,7 +681,7 @@ mext_replace_branches(handle_t *handle, > if (orig_path) > ext4_ext_drop_refs(orig_path); > get_ext_path(orig_path, orig_inode, orig_off, err); > - if (orig_path == NULL) > + if (err) > goto out; > depth = ext_depth(orig_inode); > oext = orig_path[depth].p_ext; > @@ -694,7 +696,7 @@ mext_replace_branches(handle_t *handle, > ext4_ext_drop_refs(donor_path); > get_ext_path(donor_path, donor_inode, > donor_off, err); > - if (donor_path == NULL) > + if (err) > goto out; > depth = ext_depth(donor_inode); > dext = donor_path[depth].p_ext; > @@ -1138,7 +1140,7 @@ ext4_move_extents(struct file *o_filp, s > donor_start, &len, *moved_len); > mext_double_up_read(orig_inode, donor_inode); > if (ret) > - goto out2; > + goto out; > > file_end = (i_size_read(orig_inode) - 1) >> orig_inode->i_blkbits; > block_end = block_start + len - 1; > @@ -1146,20 +1148,16 @@ ext4_move_extents(struct file *o_filp, s > len -= block_end - file_end; > > get_ext_path(orig_path, orig_inode, block_start, ret); > - if (orig_path == NULL) > - goto out2; > + if (ret) > + goto out; > > /* Get path structure to check the hole */ > get_ext_path(holecheck_path, orig_inode, block_start, ret); > - if (holecheck_path == NULL) > + if (ret) > goto out; > > depth = ext_depth(orig_inode); > ext_cur = holecheck_path[depth].p_ext; > - if (ext_cur == NULL) { > - ret = -EINVAL; > - goto out; > - } > > /* > * Get proper extent whose ee_block is beyond block_start > @@ -1282,7 +1280,7 @@ ext4_move_extents(struct file *o_filp, s > ext4_ext_drop_refs(holecheck_path); > get_ext_path(holecheck_path, orig_inode, > seq_start, ret); > - if (holecheck_path == NULL) > + if (ret) > break; > depth = holecheck_path->p_depth; > > @@ -1290,7 +1288,7 @@ ext4_move_extents(struct file *o_filp, s > if (orig_path) > ext4_ext_drop_refs(orig_path); > get_ext_path(orig_path, orig_inode, seq_start, ret); > - if (orig_path == NULL) > + if (ret) > break; > > ext_cur = holecheck_path[depth].p_ext; > @@ -1307,7 +1305,7 @@ out: > ext4_ext_drop_refs(holecheck_path); > kfree(holecheck_path); > } > -out2: > + > mext_inode_double_unlock(orig_inode, donor_inode); > > if (ret) > > -- Best Regards, Peng Tao State Key Laboratory of Networking and Switching Technology Beijing Univ. of Posts and Telecoms.