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: <20220826083612.1699194-1-floridsleeves@gmail.com>
 <CAHp75VcdqL4wYnhEi8LrxqJktA2uDzP3a6-08suJRghX=1UZsg@mail.gmail.com>
 <CAMEuxRqBEMdva3qEphvuYkFLpRjp=xg7vpqQT1oqb2AgkkG2+w@mail.gmail.com>
 <2033d06d-10a4-5a57-d650-7541c39990ee@linux.intel.com> <CAMEuxRq6wn+wakYHGtnS_vSgpcw6aNOir=KyXWb12vPrOr76pA@mail.gmail.com>
 <40e16474-99d2-2359-a545-4a437f555ec1@linux.intel.com>
In-Reply-To: <40e16474-99d2-2359-a545-4a437f555ec1@linux.intel.com>
From:   Li Zhong <floridsleeves@gmail.com>
Date:   Sat, 3 Sep 2022 16:14:59 -0700
Message-ID: <CAMEuxRpm5xNm2kEnhCSimoaCE3zSxbyoo7xUxNg74QrL7F6YUg@mail.gmail.com>
Subject: Re: [PATCH v2] drivers/tty/serial: check the return value of uart_port_check()
To:     =?UTF-8?Q?Ilpo_J=C3=A4rvinen?= <ilpo.jarvinen@linux.intel.com>
Cc:     Andy Shevchenko <andy.shevchenko@gmail.com>,
        "open list:SERIAL DRIVERS" <linux-serial@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jiri Slaby <jirislaby@kernel.org>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Tue, Aug 30, 2022 at 12:20 AM Ilpo J=C3=A4rvinen
<ilpo.jarvinen@linux.intel.com> wrote:
>
> On Mon, 29 Aug 2022, Li Zhong wrote:
>
> > On Mon, Aug 29, 2022 at 12:09 AM Ilpo J=C3=A4rvinen
> > <ilpo.jarvinen@linux.intel.com> wrote:
> > >
> > > On Sun, 28 Aug 2022, Li Zhong wrote:
> > >
> > > > On Fri, Aug 26, 2022 at 9:01 AM Andy Shevchenko
> > > > <andy.shevchenko@gmail.com> wrote:
> > > > >
> > > > > On Fri, Aug 26, 2022 at 11:38 AM Li Zhong <floridsleeves@gmail.co=
m> wrote:
> > > > > >
> > > > > > uart_port_check() will return NULL pointer when state->uart_por=
t is
> > > > > > NULL. Check the return value before dereference it to avoid
> > > > > > null-pointer-dereference error.
> > > > >
> > > > > Have you taken the locking into consideration?
> > > > > If no, please do, if yes, expand your commit message to explain w=
hy
> > > > > the current locking scheme doesn't prevent an error from happenin=
g.
> > > > >
> > > >
> > > > The locking is taken into consideration but these three checks do n=
ot need to
> > > > unlock in error-handling because unlock() will be called in the cal=
lers. Will
> > > > add the comment in v2 patch.
> > >
> > > I think he meant you should indicate why the current locking doesn't =
cover
> > > the case you're fixing, not whether this function should call unlock(=
) or
> > > not.
> > >
> >
> > Thanks for clarifications. The locking does not guarantee the return va=
lue of
> > uart_port_check()  is not NULL.
>
> Please put such explanation into the commit message like Andy was asking,
> thank you.
>

Thanks! I'll add this into the v3 patch.

> And make sure you properly mention what has changed for any new version
> of any patch you send so that Greg don't need to auto-mail you about it
> (and end up ignoring your patch).
>

I'll mention this in the commit message of new patch.

> > Actually in line 773 of this file
> > (drivers/tty/serial/serial_core.c), uart_port_check() is also called in
> > critical section but still there is check on whether the return value i=
s NULL.
>
> Existance of such a check elsewhere alone isn't enough to guarantee that
> the check is necessary (and not even that the check in that other place
> would be necessary). You need a deeper analysis than that. I'm not
> claiming its either way here, just pointing out to the direction/details
> you should consider while writing the analysis of the problem.
>

Thanks for the suggestions. We will try consider more factor into our analy=
sis
tools to reduce false postives.

>
> --
>  i.