From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754191Ab3ERGs2 (ORCPT ); Sat, 18 May 2013 02:48:28 -0400 Received: from zeniv.linux.org.uk ([195.92.253.2]:58442 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752898Ab3ERGs1 (ORCPT ); Sat, 18 May 2013 02:48:27 -0400 Date: Sat, 18 May 2013 07:48:26 +0100 From: Al Viro To: Mikulas Patocka Cc: linux-kernel@vger.kernel.org, Linus Torvalds Subject: hpfs: deadlock and race in hpfs_dir_lseek() Message-ID: <20130518064825.GX25399@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org For one thing, there's an ABBA deadlock on hpfs fs-wide lock and i_mutex in hpfs_dir_lseek() - there's a lot of methods that grab the former with the caller already holding the latter, so it must take i_mutex first. For another, locking the damn thing, carefully validating the offset, then dropping locks and assigning the offset is obviously racy. Moreover, we _must_ do hpfs_add_pos(), or the machinery in dnode.c won't modify the sucker on B-tree surgeries. Signed-off-by: Al Viro -- diff --git a/fs/hpfs/dir.c b/fs/hpfs/dir.c index 546f6d3..834ac13 100644 --- a/fs/hpfs/dir.c +++ b/fs/hpfs/dir.c @@ -33,25 +33,27 @@ static loff_t hpfs_dir_lseek(struct file *filp, loff_t off, int whence) if (whence == SEEK_DATA || whence == SEEK_HOLE) return -EINVAL; + mutex_lock(&i->i_mutex); hpfs_lock(s); /*printk("dir lseek\n");*/ if (new_off == 0 || new_off == 1 || new_off == 11 || new_off == 12 || new_off == 13) goto ok; - mutex_lock(&i->i_mutex); pos = ((loff_t) hpfs_de_as_down_as_possible(s, hpfs_inode->i_dno) << 4) + 1; while (pos != new_off) { if (map_pos_dirent(i, &pos, &qbh)) hpfs_brelse4(&qbh); else goto fail; if (pos == 12) goto fail; } - mutex_unlock(&i->i_mutex); + hpfs_add_pos(i, &filp->f_pos); ok: + filp->f_pos = new_off; hpfs_unlock(s); - return filp->f_pos = new_off; -fail: mutex_unlock(&i->i_mutex); + return new_off; +fail: /*printk("illegal lseek: %016llx\n", new_off);*/ hpfs_unlock(s); + mutex_unlock(&i->i_mutex); return -ESPIPE; }