[PATCH] drm/exynos: g2d: fix overflow of cmdlist size

[Joonyoung Shim]

Hi Tobias,

On 01/21/2017 01:05 AM, Tobias Jakobi wrote:
> Hello Joonyoung,
> 
> 
> Joonyoung Shim wrote:
>> Hi Tobias,
>>
>> On 01/19/2017 10:16 PM, Tobias Jakobi wrote:
>>> Hello Joonyoung,
>>>
>>> Joonyoung Shim wrote:
>>>> Hi Tobias,
>>>>
>>>> On 01/17/2017 11:24 PM, Tobias Jakobi wrote:
>>>>> Joonyoung Shim wrote:
>>>>>> The size of cmdlist is integer type, so it can be overflowed by cmd and
>>>>>> cmd_buf that has too big size. This patch will fix overflow issue as
>>>>>> checking maximum size of cmd and cmd_buf.
>>>>> I don't understand/see the issue here. Could you point out for which
>>>>> input of the set_cmdlist ioctl you see this particular overflow?
>>>>>
>>>>> In particular it is not clear to me which size field you're talking
>>>>> about. struct g2d_cmdlist does not have any field named 'size'.
>>>>>
>>>>
>>>> I mean size of cmdlist is
>>>> size = cmdlist->last + req->cmd_nr * 2 + req->cmd_buf_nr * 2 + 2;
>>>> in exynos_g2d_set_cmdlist_ioctl().
>>> ok, that makes things more clear. But then you need to fix the commit
>>> message. The current message implies that this 'size' you're talking
>>> about is some property of the cmdlist.
>>>
>>> Also the new comment is wrong.
>>> /* Check size of cmd and cmdlist: last 2 is about G2D_BITBLT_START */
>>>
>>> What is cmd and cmdlist? You're mixing two different things here. We are
>>> still checking the size of 'cmdlist' (which is a struct g2d_cmdlist) here.
>>>
>>> What you add is a check for the fields of 'req' (which is a struct
>>> drm_exynos_g2d_set_cmdlist).
>>>
>>> With all that said, I don't like the changes. I see the issue, but the
>>> current solution should be cleaner.
>>>
>>> I propose this. We just check req->cmd_buf_nr and req->cmd_nr against
>>> G2D_CMDLIST_DATA_NUM. This leaves us enough headrom so that the later
>>> computation (i.e. what is ending up in the local variable 'size') can
>>> never overflow.
>>>
>>
>> Agree, it's more clear to check req->cmd_buf_nr and req->cmd_nr against
>> G2D_CMDLIST_DATA_NUM.
>>
>>> For a comment for the check I propose this:
>>> "To avoid an integer overflow for the later size computations, we
>>> enforce a maximum number of submitted commands here. This limit is
>>> sufficient for all conceivable usage cases of the G2D."
>>>
>>
>> Could you post your patch to ML about this if you want?
> Sure, I've just send it together with two other small patches. Let me
> know if the current version is OK with you. I hope I did the order of
> SoB correctly (I know that Krzysztof has pointed this out lately).
> 

I don't know exactly about order of SoB but it's ok to me except
WARNING: line over 80 characters from checkpatch.pl.

Thanks for posting.