From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail115-80.sinamail.sina.com.cn (mail115-80.sinamail.sina.com.cn [218.30.115.80]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 34E05366 for ; Sat, 13 Apr 2024 08:46:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=218.30.115.80 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1712997971; cv=none; b=XRZjoiFWH9snixFWU5FkjP3uqxAazzjIZDmFxcROwPDaQPtghKKq6rdJySsZl396p8kXZiP88nRki5A81fr4xA2oO9qWZglblVp1HVWFYLBaqhH7s/aw7rfMLKYrCF0pm7bMkKbymIiYKg0aPF2bz7qedK+Fu/kg3O04GaBg9jU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1712997971; c=relaxed/simple; bh=UWWc0EfDzeo1KhUuECrIHIrSFuJFcZtoao1je9C1Tk4=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=HKu+t1YgwZYHPGk9jRi8PdFoKvjpP/nUVLKH99IrzaUhde5fhcFWvw6k1Hatue0/eeownXFM8GvMq5k3+/9p0YcCZol35ssa77r9S2M5E+7JfbVoCZM5SwrT1gvN6FNzOpuY7RRhypCGRxmha2RWZYJOv8O//PnN1mdaYyb6xx0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=sina.com; spf=pass smtp.mailfrom=sina.com; arc=none smtp.client-ip=218.30.115.80 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=sina.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=sina.com X-SMAIL-HELO: localhost.localdomain Received: from unknown (HELO localhost.localdomain)([113.88.51.22]) by sina.com (10.75.12.45) with ESMTP id 661A4624000059B8; Sat, 13 Apr 2024 16:45:26 +0800 (CST) X-Sender: hdanton@sina.com X-Auth-ID: hdanton@sina.com Authentication-Results: sina.com; spf=none smtp.mailfrom=hdanton@sina.com; dkim=none header.i=none; dmarc=none action=none header.from=hdanton@sina.com X-SMAIL-MID: 57740031457756 X-SMAIL-UIID: 1A7EB68A59634771834D1050F8AB7392-20240413-164526-1 From: Hillf Danton To: amir73il@gmail.com Cc: syzbot , linux-fsdevel@vger.kernel.org, syzkaller-bugs@googlegroups.com, linux-kernel@vger.kernel.org Subject: Re: [syzbot] Re: [syzbot] [ext4?] KASAN: slab-use-after-free Read in fsnotify Date: Sat, 13 Apr 2024 16:45:19 +0800 Message-Id: <20240413084519.1774-1-hdanton@sina.com> In-Reply-To: <00000000000095bb400615f4b0ed@google.com> References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit On Fri, 12 Apr 2024 23:42:19 -0700 Amir Goldstein > On Sat, Apr 13, 2024 at 4:41=E2=80=AFAM Hillf Danton wrote: > > > > On Thu, 11 Apr 2024 01:11:20 -0700 > > > syzbot found the following issue on: > > > > > > HEAD commit: 6ebf211bb11d Add linux-next specific files for 20240410 > > > git tree: linux-next > > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=3D1621af9d180000 > > > > #syz test https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git 6ebf211bb11d > > > > --- x/fs/notify/fsnotify.c > > +++ y/fs/notify/fsnotify.c > > @@ -101,8 +101,8 @@ void fsnotify_sb_delete(struct super_blo > > wait_var_event(fsnotify_sb_watched_objects(sb), > > !atomic_long_read(fsnotify_sb_watched_objects(sb))); > > WARN_ON(fsnotify_sb_has_priority_watchers(sb, FSNOTIFY_PRIO_CONTENT)); > > - WARN_ON(fsnotify_sb_has_priority_watchers(sb, > > - FSNOTIFY_PRIO_PRE_CONTENT)); > > + WARN_ON(fsnotify_sb_has_priority_watchers(sb, FSNOTIFY_PRIO_PRE_CONTENT)); > > + synchronize_srcu(&fsnotify_mark_srcu); > > kfree(sbinfo); > > } > > > > @@ -499,7 +499,7 @@ int fsnotify(__u32 mask, const void *dat > > { > > const struct path *path =3D fsnotify_data_path(data, data_type); > > struct super_block *sb =3D fsnotify_data_sb(data, data_type); > > - struct fsnotify_sb_info *sbinfo =3D fsnotify_sb_info(sb); > > + struct fsnotify_sb_info *sbinfo; > > struct fsnotify_iter_info iter_info = {}; > > struct mount *mnt =3D NULL; > > struct inode *inode2 =3D NULL; > > @@ -529,6 +529,8 @@ int fsnotify(__u32 mask, const void *dat > > inode2_type =3D FSNOTIFY_ITER_TYPE_PARENT; > > } > > > > + iter_info.srcu_idx =3D srcu_read_lock(&fsnotify_mark_srcu); > > + sbinfo =3D fsnotify_sb_info(sb); > > /* > > * Optimization: srcu_read_lock() has a memory barrier which can > > * be expensive. It protects walking the *_fsnotify_marks lists. > > > See comment above. This kills the optimization. > It is not worth letting all the fsnotify hooks suffer the consequence > for the edge case of calling fsnotify hook during fs shutdown. Say nothing before reading your fix. > > Also, fsnotify_sb_info(sb) in fsnotify_sb_has_priority_watchers() > is also not protected and using srcu_read_lock() there completely > nullifies the purpose of fsnotify_sb_info. > > Here is a simplified fix for fsnotify_sb_error() rebased on the > pending mm fixes for this syzbot boot failure: > > #syz test: https://github.com/amir73il/linux fsnotify-fixes Feel free to post your patch at lore because not everyone has access to sites like github. > > Jan, > > I think that all the functions called from fs shutdown context > should observe that SB_ACTIVE is cleared but wasn't sure? If you composed fix based on SB_ACTIVE that is cleared in generic_shutdown_super() with &sb->s_umount held for write, I wonder what simpler serialization than srcu you could find/create in fsnotify.