linux-hardening - Re: [PATCH][next] drm/gud: Use size_add() in call to struct

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Message-ID: <df8f30c2-7a94-110d-cc99-876979ec28c3@embeddedor.com>
Date:   Fri, 15 Sep 2023 12:56:34 -0600
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Kees Cook <keescook@...omium.org>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc:     Noralf Trønnes <noralf@...nnes.org>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>, Peter Stuge <peter@...ge.se>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] drm/gud: Use size_add() in call to struct_size()



On 9/15/23 12:52, Kees Cook wrote:
> On Fri, Sep 15, 2023 at 12:43:20PM -0600, Gustavo A. R. Silva wrote:
>> If, for any reason, the open-coded arithmetic causes a wraparound, the
>> protection that `struct_size()` adds against potential integer overflows
>> is defeated. Fix this by hardening call to `struct_size()` with `size_add()`.
>>
>> Fixes: 40e1a70b4aed ("drm: Add GUD USB Display driver")
>> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
>> ---
>>   drivers/gpu/drm/gud/gud_pipe.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/gud/gud_pipe.c b/drivers/gpu/drm/gud/gud_pipe.c
>> index d2f199ea3c11..a02f75be81f0 100644
>> --- a/drivers/gpu/drm/gud/gud_pipe.c
>> +++ b/drivers/gpu/drm/gud/gud_pipe.c
>> @@ -503,7 +503,7 @@ int gud_pipe_check(struct drm_simple_display_pipe *pipe,
>>   		return -ENOENT;
>>   
>>   	len = struct_size(req, properties,
>> -			  GUD_PROPERTIES_MAX_NUM + GUD_CONNECTOR_PROPERTIES_MAX_NUM);
>> +			  size_add(GUD_PROPERTIES_MAX_NUM, GUD_CONNECTOR_PROPERTIES_MAX_NUM));
> 
> There are both constant expressions, so there's not too much value in
> wrapping them with size_add(), but for maintaining a common coding style
> for dealing with allocation sizes, I can be convinced of the change. :)

Yep; I've found a mix of constant expressions and variables doing open-coded arithmetic
in `struct_size()`, so I'm sending them all.

> 
> Reviewed-by: Kees Cook <keescook@...omium.org>

Thanks!
--
Gustavo

> 
> 
>>   	req = kzalloc(len, GFP_KERNEL);
>>   	if (!req)
>>   		return -ENOMEM;
>> -- 
>> 2.34.1
>>
>