linux-kernel - Re: [PATCH 2/2] auxdisplay: charlcd: checking for pointer reference before dereferencing

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Message-ID: <CANiq72kgm-5CidoN8VRLnWokiDSWsQcMFbaUd4WKOnbPsON9RQ@mail.gmail.com>
Date:   Mon, 8 Nov 2021 12:58:33 +0100
From:   Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To:     Luiz Sampaio <sampaio.ime@...il.com>
Cc:     Miguel Ojeda <ojeda@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] auxdisplay: charlcd: checking for pointer reference
 before dereferencing

On Sun, Nov 7, 2021 at 4:03 PM Luiz Sampaio <sampaio.ime@...il.com> wrote:
>
> Check if the pointer lcd->ops->init_display exists before dereferencing it.
> If a driver called charlcd_init() without defining the ops, this would
> return segmentation fault, as happened to me when implementing a charlcd
> driver.  Checking the pointer before dereferencing protects from
> segmentation fault.

It can't hurt -- thanks! I think `EINVAL` makes more sense here, also
we could use `WARN_ON`:

    if (WARN_ON(!lcd->ops->init_display))
        return -EINVAL;

Cheers,
Miguel