From: Jan Kara Subject: [PATCH] ext4: Fix SEEK_HOLE/SEEK_DATA for blocksize < pagesize Date: Fri, 28 Jul 2017 13:16:37 +0200 Message-ID: <20170728111637.12473-1-jack@suse.cz> Cc: , Andreas Gruenbacher , Jan Kara , stable@vger.kernel.org To: Ted Tso Return-path: Received: from mx2.suse.de ([195.135.220.15]:55682 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751071AbdG1LQm (ORCPT ); Fri, 28 Jul 2017 07:16:42 -0400 Sender: linux-ext4-owner@vger.kernel.org List-ID: ext4_find_unwritten_pgoff() does not properly handle a situation when starting index is in the middle of a page and blocksize < pagesize. The following command shows the bug on filesystem with 1k blocksize: xfs_io -f -c "falloc 0 4k" \ -c "pwrite 1k 1k" \ -c "pwrite 3k 1k" \ -c "seek -a -r 0" foo In this example, neither lseek(fd, 1024, SEEK_HOLE) nor lseek(fd, 2048, SEEK_DATA) will return the correct result. Fix the problem by neglecting buffers in a page before starting offset. Reported-by: Andreas Gruenbacher CC: stable@vger.kernel.org Signed-off-by: Jan Kara --- fs/ext4/file.c | 3 +++ 1 file changed, 3 insertions(+) This is an easy fix for the SEEK_HOLE/SEEK_DATA bug Andreas found. Longer term we want to move ext4 to use page_cache_seek_hole_data() however for stable backporting this is more suitable. diff --git a/fs/ext4/file.c b/fs/ext4/file.c index b221d0b546b0..8ba34cbe8fe7 100644 --- a/fs/ext4/file.c +++ b/fs/ext4/file.c @@ -530,6 +530,8 @@ static int ext4_find_unwritten_pgoff(struct inode *inode, lastoff = page_offset(page); bh = head = page_buffers(page); do { + if (lastoff + bh->b_size <= startoff) + goto next; if (buffer_uptodate(bh) || buffer_unwritten(bh)) { if (whence == SEEK_DATA) @@ -544,6 +546,7 @@ static int ext4_find_unwritten_pgoff(struct inode *inode, unlock_page(page); goto out; } +next: lastoff += bh->b_size; bh = bh->b_this_page; } while (bh != head); -- 2.12.3