linux-kernel - Re: [PATCH 1/2] media: venus: fix OOB read issue due to double read

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Message-ID: <4cfc1fe1-2fab-4256-9ce2-b4a0aad1069e@linaro.org>
Date: Fri, 17 Jan 2025 10:25:18 +0000
From: Bryan O'Donoghue <bryan.odonoghue@...aro.org>
To: Vedang Nagar <quic_vnagar@...cinc.com>,
 Stanimir Varbanov <stanimir.k.varbanov@...il.com>,
 Vikash Garodia <quic_vgarodia@...cinc.com>,
 Mauro Carvalho Chehab <mchehab@...nel.org>
Cc: linux-media@...r.kernel.org, linux-arm-msm@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] media: venus: fix OOB read issue due to double read

On 17/01/2025 08:39, Vedang Nagar wrote:
> Below is the first read where dwords is being validated properly with the checks.
> dwords = *rd_ptr >> 2;
> 
> Whereas the same address is being read for the second time:
> memcpy(pkt, rd_ptr, dwords << 2);
> 
> For the second read the value is not validated which may get updated from the firmware
> leading to incorrect memcpy into the packet and may lead to OOB read access while accessing
> the packet.

So you are saying that pkt points to memory that the firmware and host 
can simultaneously access.

The question is - if the length value can change between one read and 
another read - how do you trust the _content_ of the packet ?

Surely the right thing to do is to take a _copy_ of the entire frame and 
act on that frame exclusively on the host side ?

If I receive a frame, and read length X.

Then I need to re-read that frame because length may now by X+3.

This implies the _data_ in the frame has changed.

What exactly is the valid lifetime of this data from HFI RX interrupt ?

---
bod