From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from zeniv.linux.org.uk ([195.92.253.2]:55870 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751000AbeEJUIC (ORCPT ); Thu, 10 May 2018 16:08:02 -0400 Date: Thu, 10 May 2018 21:07:53 +0100 From: Al Viro To: Tetsuo Handa Cc: miklos@szeredi.hu, syzbot , syzkaller-bugs@googlegroups.com, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH] fuse: don't keep inode-less dentry at fuse_ctl_add_dentry(). Message-ID: <20180510200753.GU30522@ZenIV.linux.org.uk> References: <000000000000c0a706056ad69897@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Wed, May 09, 2018 at 07:58:58PM +0900, Tetsuo Handa wrote: > >From 9f41081f8bd6762a6f629e5e23e6d07a62bba69c Mon Sep 17 00:00:00 2001 > From: Tetsuo Handa > Date: Sat, 28 Apr 2018 11:24:09 +0900 > Subject: [PATCH] fuse: don't keep inode-less dentry at fuse_ctl_add_dentry(). > > syzbot is reporting NULL pointer dereference at fuse_ctl_remove_conn() [1]. > Since fc->ctl_ndents is incremented by fuse_ctl_add_conn() when new_inode() > failed, fuse_ctl_remove_conn() reaches an inode-less dentry and tries to > clear d_inode(dentry)->i_private field. Fix this by calling dput() rather > than incrementing fc->ctl_ndents when new_inode() failed. That looks bloody awful. Sure, everything that accesses fc->ctl_dentry is synchronous with this, but it would've been much easier to follow if shoving dentry into that array happened only after it's been fully set up. Incidentally, there's a nasty headache waiting to happen in that code - consider a twit mounting something on that. And think what happens when connection gets shut down...