linux-kernel - Re: [PATCH v2] drivers/tty/serial: check the return value of uart_port

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Message-ID: <CAMEuxRpm5xNm2kEnhCSimoaCE3zSxbyoo7xUxNg74QrL7F6YUg@mail.gmail.com>
Date:   Sat, 3 Sep 2022 16:14:59 -0700
From:   Li Zhong <floridsleeves@...il.com>
To:     Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc:     Andy Shevchenko <andy.shevchenko@...il.com>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>
Subject: Re: [PATCH v2] drivers/tty/serial: check the return value of uart_port_check()

On Tue, Aug 30, 2022 at 12:20 AM Ilpo Järvinen
<ilpo.jarvinen@...ux.intel.com> wrote:
>
> On Mon, 29 Aug 2022, Li Zhong wrote:
>
> > On Mon, Aug 29, 2022 at 12:09 AM Ilpo Järvinen
> > <ilpo.jarvinen@...ux.intel.com> wrote:
> > >
> > > On Sun, 28 Aug 2022, Li Zhong wrote:
> > >
> > > > On Fri, Aug 26, 2022 at 9:01 AM Andy Shevchenko
> > > > <andy.shevchenko@...il.com> wrote:
> > > > >
> > > > > On Fri, Aug 26, 2022 at 11:38 AM Li Zhong <floridsleeves@...il.com> wrote:
> > > > > >
> > > > > > uart_port_check() will return NULL pointer when state->uart_port 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 why
> > > > > the current locking scheme doesn't prevent an error from happening.
> > > > >
> > > >
> > > > The locking is taken into consideration but these three checks do not need to
> > > > unlock in error-handling because unlock() will be called in the callers. 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 value 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 is 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 analysis
tools to reduce false postives.

>
> --
>  i.