Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <20230515095956.17898-1-zyytlz.wz@163.com> <kyzmstq5dodvgpmd7rge3gtdikbbpauw6fide7vccgii4xtb6n@bwrwjsx4ylmx>
In-Reply-To: <kyzmstq5dodvgpmd7rge3gtdikbbpauw6fide7vccgii4xtb6n@bwrwjsx4ylmx>
From:   Zheng Hacker <hackerzheng666@gmail.com>
Date:   Fri, 21 Jul 2023 16:15:19 +0800
Message-ID: <CAJedcCzmx02bfa22QezE8mu-iDsSdSy_oApT2ozCWO8O-8MJEQ@mail.gmail.com>
Subject: Re: [PATCH] fs/jfs: Add a mutex named txEnd_lmLogClose_mutex to
 prevent a race condition between txEnd and lmLogClose functions
To:     =?UTF-8?Q?Michal_Koutn=C3=BD?= <mkoutny@suse.com>
Cc:     Zheng Wang <zyytlz.wz@163.com>, shaggy@kernel.org,
        jfs-discussion@lists.sourceforge.net, linux-kernel@vger.kernel.org,
        1395428693sheep@gmail.com, alex000young@gmail.com,
        security@kernel.org
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

Hello Michal,


Michal Koutn=C3=BD <mkoutny@suse.com> =E4=BA=8E2023=E5=B9=B47=E6=9C=8820=E6=
=97=A5=E5=91=A8=E5=9B=9B 17:56=E5=86=99=E9=81=93=EF=BC=9A
>
> Hello Zheng.
>
> On Mon, May 15, 2023 at 05:59:56PM +0800, Zheng Wang <zyytlz.wz@163.com> =
wrote:
> > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> > BUG: KASAN: slab-use-after-free in instrument_atomic_write include/linu=
x/instrumented.h:87 [inline]
> > BUG: KASAN: slab-use-after-free in clear_bit include/asm-generic/bitops=
/instrumented-atomic.h:41 [inline]
> > BUG: KASAN: slab-use-after-free in txEnd+0x2a3/0x5a0 fs/jfs/jfs_txnmgr.=
c:535
> > Write of size 8 at addr ffff888021bee840 by task jfsCommit/130
> >
> > CPU: 3 PID: 130 Comm: jfsCommit Not tainted 6.3.0-rc7-pasta #1
>
> Is this still pertinent with the current mainline? (There were some
> changes to jfs.)

Thank you very much for your reply and suggestion. I thought that this
BUG still exists in the current mainline kernel version. Since I am
not very familiar with this part of the code, I am not sure if the
proposed fix is correct.

>
> > Through analysis, it was found that a race condition occurred between t=
wo
> > functions lmLogClose and txEnd, which were executed in different thread=
s.
> > The possible sequence is as follows:
> >
> > -----------------------------------------------------------------------=
--
> > cpu1(free thread)        |        cpu2(use thread)
> > -----------------------------------------------------------------------=
--
> > lmLogClose               |        txEnd
> >                          |        log =3D JFS_SBI(tblk->sb)->log;
> > sbi->log =3D NULL;         |
> > kfree(log); [1] free log |
> >                          |        clear_bit(log_FLUSH, &log->flag); [2]=
 UAF
>
> That looks sane to a by-passer.
>
> > Fix it by add a mutex lock between lmLogClose and txEnd:
>
> It doesn't feel right wrt "lock data, not code" heuristics.
> And when I apply that, it turns out there's already jfs_log_mutex.
> I'd suggest you explain more why a new lock is needed (if that's the
> preferred solutino).

You're right, I think my fix method is not a good solution. Hoping you
and other developers can help fix it.

>
> Thanks,
> Michal

Once again, I appreciate your help and will take your feedback into
consideration when working on a solution.

Best regards,
Zheng