linux-kernel - Re: [PATCH] dispnv50: atom: fix an incorrect NULL check on list iterator

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Message-ID: <CACvgo50pK3rr5UH_FyfR1pADmPRjEawi43cAecoaz7nM5AFgBg@mail.gmail.com>
Date:   Sun, 27 Mar 2022 16:59:28 +0100
From:   Emil Velikov <emil.l.velikov@...il.com>
To:     Xiaomeng Tong <xiam0nd.tong@...il.com>
Cc:     Ben Skeggs <bskeggs@...hat.com>, Karol Herbst <kherbst@...hat.com>,
        Lyude <lyude@...hat.com>, Dave Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        ML nouveau <nouveau@...ts.freedesktop.org>,
        yangyingliang@...wei.com,
        "Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>,
        ML dri-devel <dri-devel@...ts.freedesktop.org>,
        "# 3.13+" <stable@...r.kernel.org>
Subject: Re: [PATCH] dispnv50: atom: fix an incorrect NULL check on list iterator

On Sun, 27 Mar 2022 at 08:39, Xiaomeng Tong <xiam0nd.tong@...il.com> wrote:
>
> The bug is here:
>         return encoder;
>
> The list iterator value 'encoder' will *always* be set and non-NULL
> by drm_for_each_encoder_mask(), so it is incorrect to assume that the
> iterator value will be NULL if the list is empty or no element found.
> Otherwise it will bypass some NULL checks and lead to invalid memory
> access passing the check.
>
> To fix this bug, just return 'encoder' when found, otherwise return
> NULL.
>

Isn't this covered by the upcoming list* iterator rework [1] or is
this another iterator glitch?
IMHO we should be looking at fixing the implementation and not the
hundreds of users through the kernel.

HTH
-Emil
[1] https://lwn.net/Articles/887097/