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

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Message-ID: <060f4dbe-63d6-1c60-14ca-553bf1536e5a@quicinc.com>
Date:   Fri, 11 Aug 2023 21:32:39 +0530
From:   Vikash Garodia <quic_vgarodia@...cinc.com>
To:     Bryan O'Donoghue <bryan.odonoghue@...aro.org>,
        <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 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.

> 
> ---
> bod