linux-kernel - Re: [PATCH 1/4] media: venus: hfi_parser: add check to avoid out of bound access

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Message-ID: <ql6hftuo7udkqachofws6lcpwx7sbjakonoehm7zsh43kqndsf@rwmiwqngldn2>
Date: Thu, 7 Nov 2024 15:22:15 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Vikash Garodia <quic_vgarodia@...cinc.com>
Cc: Bryan O'Donoghue <bryan.odonoghue@...aro.org>, 
	Stanimir Varbanov <stanimir.k.varbanov@...il.com>, Mauro Carvalho Chehab <mchehab@...nel.org>, 
	linux-media@...r.kernel.org, linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	stable@...r.kernel.org
Subject: Re: [PATCH 1/4] media: venus: hfi_parser: add check to avoid out of
 bound access

On Thu, Nov 07, 2024 at 06:32:33PM +0530, Vikash Garodia wrote:
> 
> On 11/7/2024 5:37 PM, Bryan O'Donoghue wrote:
> > On 07/11/2024 10:41, Dmitry Baryshkov wrote:
> >>> init_codecs() parses the payload received from firmware and . I don't think we
> >>> can control this part when we have something like this from a malicious firmware
> >>> payload
> >>> HFI_PROPERTY_PARAM_CODEC_SUPPORTED
> >>> HFI_PROPERTY_PARAM_CODEC_SUPPORTED
> >>> HFI_PROPERTY_PARAM_CODEC_SUPPORTED
> >>> ...
> >>> Limiting it to second iteration would restrict the functionality when property
> >>> HFI_PROPERTY_PARAM_CODEC_SUPPORTED is sent for supported number of codecs.
> >> If you can have a malicious firmware (which is owned and signed by
> >> Qualcomm / OEM), then you have to be careful and skip duplicates. So
> >> instead of just adding new cap to core->caps, you have to go through
> >> that array, check that you are not adding a duplicate (and report a
> >> [Firmware Bug] for duplicates), check that there is an empty slot, etc.
> >>
> >> Just ignoring the "extra" entries is not enough.
> Thinking of something like this
> 
> for_each_set_bit(bit, &core->dec_codecs, MAX_CODEC_NUM) {
>     if (core->codecs_count >= MAX_CODEC_NUM)
>         return;
>     cap = &caps[core->codecs_count++];
>     if (cap->codec == BIT(bit)) --> each code would have unique bitfield
>         return;

This won't work and it's pretty obvious why.

> > +1
> > 
> > This is a more rational argument. If you get a second message, you should surely
> > reinit the whole array i.e. update the array with the new list, as opposed to
> > throwing away the second message because it over-indexes your local storage..
> That would be incorrect to overwrite the array with new list, whenever new
> payload is received.

I'd say, don't overwrite the array. Instead the driver should extend it
with the new information.

> 
> Regards,
> Vikash

-- 
With best wishes
Dmitry