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 <20220328020902.19369-1-xiam0nd.tong@gmail.com>
In-Reply-To: <20220328020902.19369-1-xiam0nd.tong@gmail.com>
From:   Emil Velikov <emil.l.velikov@gmail.com>
Date:   Tue, 29 Mar 2022 11:59:06 +0100
Message-ID: <CACvgo5342xQHb07FVK4beXWgFexZR0LyODEqemE3y1subnEw1Q@mail.gmail.com>
Subject: Re: [PATCH] dispnv50: atom: fix an incorrect NULL check on list iterator
To:     Xiaomeng Tong <xiam0nd.tong@gmail.com>
Cc:     Dave Airlie <airlied@linux.ie>, Ben Skeggs <bskeggs@redhat.com>,
        Daniel Vetter <daniel@ffwll.ch>,
        ML dri-devel <dri-devel@lists.freedesktop.org>,
        Karol Herbst <kherbst@redhat.com>,
        "Linux-Kernel@Vger. Kernel. Org" <linux-kernel@vger.kernel.org>,
        Lyude <lyude@redhat.com>,
        ML nouveau <nouveau@lists.freedesktop.org>,
        "# 3.13+" <stable@vger.kernel.org>, yangyingliang@huawei.com
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On Mon, 28 Mar 2022 at 03:09, Xiaomeng Tong <xiam0nd.tong@gmail.com> wrote:
>
> on Sun, 27 Mar 2022 16:59:28 +0100, Emil Velikov wrote:
> > On Sun, 27 Mar 2022 at 08:39, Xiaomeng Tong <xiam0nd.tong@gmail.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?
>
> Actually, it is a part of the upcoming work.
>
> > 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/
>
> Yes, you are right. This has also been taken into account by the upcoming
> list iterator rework to avoid a lot uesr' changes as much as possible.
>
> However, this patch is fixing a potential bug caused by incorrect use of
> list iterator outside the loop, which can not be fixed by the implementation
> itself.
>

I see, thanks for the information o/

-Emil