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=-13.4 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,USER_IN_DEF_DKIM_WL 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 F17FAC10F00 for ; Fri, 6 Mar 2020 15:36:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CC60A20726 for ; Fri, 6 Mar 2020 15:36:51 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="pdzfVkRp" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727191AbgCFPgu (ORCPT ); Fri, 6 Mar 2020 10:36:50 -0500 Received: from mail-oi1-f193.google.com ([209.85.167.193]:35159 "EHLO mail-oi1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727137AbgCFPgu (ORCPT ); Fri, 6 Mar 2020 10:36:50 -0500 Received: by mail-oi1-f193.google.com with SMTP id c1so2939342oiy.2 for ; Fri, 06 Mar 2020 07:36:48 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=aIS3j9BcsIx1974rQkdX3Sq/wS4nhMN+kP4/ppiopJQ=; b=pdzfVkRpdhCdinsJQyA2PpGXMwl9diPaAtQ+q5PW7umYSE8oOsh+l4A7IkWmbd5V30 FVXy2Y5U+5S7vPuSIkuWSXFTasDAGkFOEf1jlNfn2DSNAz37CkwOZZ/So73T1EpJeKsy Z0uixE4WN+DrWt9CriO18kAzqHWWy3qebwSLleITjbms4v81y6Jq9tZRtNWNGYmEaX/Z n7tiP8mwgfqQ9F+kl4DnTqxA0TRHNrnQuFlfAL0kPfG5fBhEkkidL3UXquSbhYhIeo5X kYpplD1y0KZNmODQs8TfxBxhueX2QCEv381klgHQxcoaX9sY/bszhuiSfVzkR1xt66XO wEQg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=aIS3j9BcsIx1974rQkdX3Sq/wS4nhMN+kP4/ppiopJQ=; b=f6TJ5oIED4pJuN8F9xDIR8Tbb1p4jW1JECag24S9wzTFhLhcY7ppo8RSRfawvrBtcu JY6ACIvge0OiBonIF7ucA7jSL+KpeoxBEN8feJlmUGUqPUfxdbdeFSgK61Ejo3+n/Epe LMUNRZNlvxiAIavIONFyV/oEvJgevBfFA9Y5KSFuHg0Yfkp0EpMrpmD5Z5lB2id0uuxi 7YNFdCZqvmnNX7JGwlnxdNMa0HjDBttqeUTw4m8Eq6j8kczWLdOCO6GX1PjD8ol0bl/5 xJkWxSQGBbjkfUNgxBHHVuL2gOYN7i8EorkwN2acOeDrhV4LR8lCB1aPtoD3asIk5GiW cKBw== X-Gm-Message-State: ANhLgQ3k5ImeGEIx1XS5EmAdYVHnp2OdpJU6t36vYRqEgV3DKXHWYa3D j7P0y/C8ZV62yZ6snOoPOtwGgbweTNNJgK9zBCmgcA== X-Google-Smtp-Source: ADFU+vvgF4FhHryXSvnABcW3w8OiD7DynVdUdHWARYq/viqNv1B+cG0awG7CYgS9jYS7UtPoQdF/YFo5AlaEqpOqD50= X-Received: by 2002:a05:6808:8d0:: with SMTP id k16mr3048626oij.68.1583509007480; Fri, 06 Mar 2020 07:36:47 -0800 (PST) MIME-Version: 1.0 References: <00000000000067c6df059df7f9f5@google.com> <3f805e51-1db7-3e57-c9a3-15a20699ea54@kernel.dk> <075e7fbe-aeec-cb7d-9338-8eb4e1576293@kernel.dk> In-Reply-To: <075e7fbe-aeec-cb7d-9338-8eb4e1576293@kernel.dk> From: Jann Horn Date: Fri, 6 Mar 2020 16:36:20 +0100 Message-ID: Subject: Re: KASAN: use-after-free Read in percpu_ref_switch_to_atomic_rcu To: Jens Axboe , "Paul E . McKenney" Cc: Dmitry Vyukov , syzbot , Al Viro , io-uring , linux-fsdevel , Borislav Petkov , "H. Peter Anvin" , LKML , Ingo Molnar , Peter Zijlstra , syzkaller-bugs , Thomas Gleixner , tony.luck@intel.com, "the arch/x86 maintainers" , Dan Carpenter Content-Type: text/plain; charset="UTF-8" Sender: io-uring-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On Fri, Mar 6, 2020 at 4:34 PM Jens Axboe wrote: > On 3/6/20 7:57 AM, Jann Horn wrote: > > +paulmck > > > > On Wed, Mar 4, 2020 at 3:40 PM Jens Axboe wrote: > >> On 3/4/20 12:59 AM, Dmitry Vyukov wrote: > >>> On Fri, Feb 7, 2020 at 9:14 AM syzbot > >>> wrote: > >>>> > >>>> Hello, > >>>> > >>>> syzbot found the following crash on: > >>>> > >>>> HEAD commit: 4c7d00cc Merge tag 'pwm/for-5.6-rc1' of git://git.kernel.o.. > >>>> git tree: upstream > >>>> console output: https://syzkaller.appspot.com/x/log.txt?x=12fec785e00000 > >>>> kernel config: https://syzkaller.appspot.com/x/.config?x=e162021ddededa72 > >>>> dashboard link: https://syzkaller.appspot.com/bug?extid=e017e49c39ab484ac87a > >>>> compiler: clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81) > >>>> > >>>> Unfortunately, I don't have any reproducer for this crash yet. > >>>> > >>>> IMPORTANT: if you fix the bug, please add the following tag to the commit: > >>>> Reported-by: syzbot+e017e49c39ab484ac87a@syzkaller.appspotmail.com > >>> > >>> +io_uring maintainers > >>> > >>> Here is a repro: > >>> https://gist.githubusercontent.com/dvyukov/6b340beab6483a036f4186e7378882ce/raw/cd1922185516453c201df8eded1d4b006a6d6a3a/gistfile1.txt > >> > >> I've queued up a fix for this: > >> > >> https://git.kernel.dk/cgit/linux-block/commit/?h=io_uring-5.6&id=9875fe3dc4b8cff1f1b440fb925054a5124403c3 > > > > I believe that this fix relies on call_rcu() having FIFO ordering; but > > > > says: > > > > | call_rcu() normally acts only on CPU-local state[...] It simply > > enqueues the rcu_head structure on a per-CPU list, > > > > Is this fix really correct? > > That's a good point, there's a potentially stronger guarantee we need > here that isn't "nobody is inside an RCU critical section", but rather > that we're depending on a previous call_rcu() to have happened. Hence I > think you are right - it'll shrink the window drastically, since the > previous callback is already queued up, but it's not a full close. > > Hmm... You could potentially hack up the semantics you want by doing a call_rcu() whose callback does another call_rcu(), or something like that - but I'd like to hear paulmck's opinion on this first.