linux-kernel - Re: [PATCH v2 4/4] venus: hfi_parser: Add check to keep the number of codecs within range

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Date:   Fri, 11 Aug 2023 19:51:35 +0100
From:   Bryan O'Donoghue <bryan.odonoghue@...aro.org>
To:     Vikash Garodia <quic_vgarodia@...cinc.com>,
        stanimir.k.varbanov@...il.com, agross@...nel.org,
        andersson@...nel.org, konrad.dybcio@...aro.org, mchehab@...nel.org,
        hans.verkuil@...co.com, tfiga@...omium.org
Cc:     linux-media@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v2 4/4] venus: hfi_parser: Add check to keep the number of
 codecs within range

On 11/08/2023 17:02, Vikash Garodia wrote:
> 
> 
> On 8/11/2023 4:11 PM, Bryan O'Donoghue wrote:
>> On 11/08/2023 09:49, Vikash Garodia wrote:
>>>
>>> On 8/11/2023 2:12 PM, Bryan O'Donoghue wrote:
>>>> On 11/08/2023 07:04, Vikash Garodia wrote:
>>>>>
>>>>> On 8/10/2023 5:03 PM, Bryan O'Donoghue wrote:
>>>>>> On 10/08/2023 03:25, Vikash Garodia wrote:
>>>>>>> +    if (hweight_long(core->dec_codecs) + hweight_long(core->enc_codecs) >
>>>>>>> MAX_CODEC_NUM)
>>>>>>> +        return;
>>>>>>> +
>>>>>>
>>>>>> Shouldn't this be >= ?
>>>>> Not needed. Lets take a hypothetical case when core->dec_codecs has initial 16
>>>>> (0-15) bits set and core->enc_codecs has next 16 bits (16-31) set. The bit
>>>>> count
>>>>> would be 32. The codec loop after this check would run on caps array index
>>>>> 0-31.
>>>>> I do not see a possibility for OOB access in this case.
>>>>>
>>>>>>
>>>>>> struct hfi_plat_caps caps[MAX_CODEC_NUM];
>>>>>>
>>>>>> ---
>>>>>> bod
>>>>>>
>>>>
>>>> Are you not doing a general defensive coding pass in this series ie
>>>>
>>>> "[PATCH v2 2/4] venus: hfi: fix the check to handle session buffer requirement"
>>>
>>> In "PATCH v2 2/4", there is a possibility if the check does not consider "=".
>>> Here in this patch, I do not see a possibility.
>>>
>>>>
>>>> ---
>>>> bod
>>
>> But surely hweight_long(core->dec_codecs) + hweight_long(core->enc_codecs) ==
>> MAX_CODEC_NUM is an invalid offset ?
> 
> No, it isn't. Please run through the loop with the bitmasks added upto 32 and
> see if there is a possibility of OOB.

IDK Vikash, the logic here seems suspect.

We have two loops that check for up to 32 indexes per loop. Why not have 
a capabilities index that can accommodate all 64 bits ?

Why is it valid to have 16 encoder bits and 16 decoder bits but invalid 
to have 16 encoder bits with 17 decoder bits ? While at the same time 
valid to have 0 encoder bits but 17 decoder bits ?

---
bod