From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E1CDCC433DF for ; Mon, 15 Jun 2020 07:38:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C605D20707 for ; Mon, 15 Jun 2020 07:38:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728599AbgFOHim (ORCPT ); Mon, 15 Jun 2020 03:38:42 -0400 Received: from mx2.suse.de ([195.135.220.15]:35492 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728465AbgFOHim (ORCPT ); Mon, 15 Jun 2020 03:38:42 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id C138FAE39; Mon, 15 Jun 2020 07:38:42 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id E64861E1289; Mon, 15 Jun 2020 09:38:36 +0200 (CEST) Date: Mon, 15 Jun 2020 09:38:36 +0200 From: Jan Kara To: "Eric W. Biederman" Cc: syzbot , a@unstable.cc, adobriyan@gmail.com, akpm@linux-foundation.org, alex.dewar@gmx.co.uk, amir73il@gmail.com, anton.ivanov@cambridgegreys.com, b.a.t.m.a.n@lists.open-mesh.org, davem@davemloft.net, jack@suse.cz, jdike@addtoit.com, kuba@kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-um@lists.infradead.org, mareklindner@neomailbox.ch, netdev@vger.kernel.org, richard@nod.at, sfr@canb.auug.org.au, sven@narfation.org, sw@simonwunderlich.de, syzkaller-bugs@googlegroups.com Subject: Re: [PATCH] proc: Use new_inode not new_inode_pseudo Message-ID: <20200615073836.GD9449@quack2.suse.cz> References: <000000000000d788c905a7dfa3f4@google.com> <87mu58p02g.fsf@x220.int.ebiederm.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87mu58p02g.fsf@x220.int.ebiederm.org> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Fri 12-06-20 14:15:51, Eric W. Biederman wrote: > > Recently syzbot reported that unmounting proc when there is an ongoing > inotify watch on the root directory of proc could result in a use > after free when the watch is removed after the unmount of proc > when the watcher exits. > > Commit 69879c01a0c3 ("proc: Remove the now unnecessary internal mount > of proc") made it easier to unmount proc and allowed syzbot to see the > problem, but looking at the code it has been around for a long time. > > Looking at the code the fsnotify watch should have been removed by > fsnotify_sb_delete in generic_shutdown_super. Unfortunately the inode > was allocated with new_inode_pseudo instead of new_inode so the inode > was not on the sb->s_inodes list. Which prevented > fsnotify_unmount_inodes from finding the inode and removing the watch > as well as made it so the "VFS: Busy inodes after unmount" warning > could not find the inodes to warn about them. > > Make all of the inodes in proc visible to generic_shutdown_super, > and fsnotify_sb_delete by using new_inode instead of new_inode_pseudo. > The only functional difference is that new_inode places the inodes > on the sb->s_inodes list. > > I wrote a small test program and I can verify that without changes it > can trigger this issue, and by replacing new_inode_pseudo with > new_inode the issues goes away. > > Cc: stable@vger.kernel.org > Link: https://lkml.kernel.org/r/000000000000d788c905a7dfa3f4@google.com > Reported-by: syzbot+7d2debdcdb3cb93c1e5e@syzkaller.appspotmail.com > Fixes: 0097875bd415 ("proc: Implement /proc/thread-self to point at the directory of the current thread") > Fixes: 021ada7dff22 ("procfs: switch /proc/self away from proc_dir_entry") > Fixes: 51f0885e5415 ("vfs,proc: guarantee unique inodes in /proc") > Signed-off-by: "Eric W. Biederman" Thanks for analysing this! I agree with the analysis and the patch looks good to me. You can add: Reviewed-by: Jan Kara Honza > --- > fs/proc/inode.c | 2 +- > fs/proc/self.c | 2 +- > fs/proc/thread_self.c | 2 +- > 3 files changed, 3 insertions(+), 3 deletions(-) > > diff --git a/fs/proc/inode.c b/fs/proc/inode.c > index f40c2532c057..28d6105e908e 100644 > --- a/fs/proc/inode.c > +++ b/fs/proc/inode.c > @@ -617,7 +617,7 @@ const struct inode_operations proc_link_inode_operations = { > > struct inode *proc_get_inode(struct super_block *sb, struct proc_dir_entry *de) > { > - struct inode *inode = new_inode_pseudo(sb); > + struct inode *inode = new_inode(sb); > > if (inode) { > inode->i_ino = de->low_ino; > diff --git a/fs/proc/self.c b/fs/proc/self.c > index ca5158fa561c..72cd69bcaf4a 100644 > --- a/fs/proc/self.c > +++ b/fs/proc/self.c > @@ -43,7 +43,7 @@ int proc_setup_self(struct super_block *s) > inode_lock(root_inode); > self = d_alloc_name(s->s_root, "self"); > if (self) { > - struct inode *inode = new_inode_pseudo(s); > + struct inode *inode = new_inode(s); > if (inode) { > inode->i_ino = self_inum; > inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode); > diff --git a/fs/proc/thread_self.c b/fs/proc/thread_self.c > index ac284f409568..a553273fbd41 100644 > --- a/fs/proc/thread_self.c > +++ b/fs/proc/thread_self.c > @@ -43,7 +43,7 @@ int proc_setup_thread_self(struct super_block *s) > inode_lock(root_inode); > thread_self = d_alloc_name(s->s_root, "thread-self"); > if (thread_self) { > - struct inode *inode = new_inode_pseudo(s); > + struct inode *inode = new_inode(s); > if (inode) { > inode->i_ino = thread_self_inum; > inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode); > -- > 2.20.1 > -- Jan Kara SUSE Labs, CR