linux-hardening - Re: [PATCH v2] crypto: Use struct

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Date:   Wed, 18 May 2022 14:21:13 +0800
From:   "Guozihua (Scott)" <guozihua@...wei.com>
To:     "Gustavo A. R. Silva" <gustavoars@...nel.org>
CC:     <keyrings@...r.kernel.org>, <linux-crypto@...r.kernel.org>,
        <davem@...emloft.net>, <dhowells@...hat.com>,
        <herbert@...dor.apana.org.au>, <linux-hardening@...r.kernel.org>
Subject: Re: [PATCH v2] crypto: Use struct_size() helper in kmalloc()

On 2022/5/18 12:55, Gustavo A. R. Silva wrote:
> On Wed, May 18, 2022 at 08:56:39AM +0800, GUO Zihua wrote:
>> Make use of struct_size() heler for structures containing flexible array
>> member instead of sizeof() which prevents potential issues as well as
>> addressing the following sparse warning:
>>
>> crypto/asymmetric_keys/asymmetric_type.c:155:23: warning: using sizeof
>> on a flexible structure
>> crypto/asymmetric_keys/asymmetric_type.c:247:28: warning: using sizeof
>> on a flexible structure
> 
> The warnings above are not silenced with this patch as struct_size()
> internally use sizeof on the struct-with-flex-array.
> 
> However, the use of struct_size() instead of the open-coded expressions
> in the calls to kmalloc() is correct.
> 
>>
>> Reference: https://github.com/KSPP/linux/issues/174
> 
> I updated this issue on the issue tracker. Please, from now on, just
> use that issue as a list of potential open-coded instances to be
> audited. :)
> 
>>
>> Signed-off-by: GUO Zihua <guozihua@...wei.com>
> 
> Reviewed-by: Gustavo A. R. Silva <gustavoars@...nel.org>
> 
> Thanks
> --
> Gustavo
> 
>>
>> ---
>>
>> v2:
>>      Use size_add() helper following Kees Cook's suggestion.
>> ---
>>   crypto/asymmetric_keys/asymmetric_type.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/crypto/asymmetric_keys/asymmetric_type.c b/crypto/asymmetric_keys/asymmetric_type.c
>> index 41a2f0eb4ce4..e020222b1fe5 100644
>> --- a/crypto/asymmetric_keys/asymmetric_type.c
>> +++ b/crypto/asymmetric_keys/asymmetric_type.c
>> @@ -152,7 +152,7 @@ struct asymmetric_key_id *asymmetric_key_generate_id(const void *val_1,
>>   {
>>   	struct asymmetric_key_id *kid;
>>   
>> -	kid = kmalloc(sizeof(struct asymmetric_key_id) + len_1 + len_2,
>> +	kid = kmalloc(struct_size(kid, data, size_add(len_1, len_2)),
>>   		      GFP_KERNEL);
>>   	if (!kid)
>>   		return ERR_PTR(-ENOMEM);
>> @@ -244,7 +244,7 @@ struct asymmetric_key_id *asymmetric_key_hex_to_key_id(const char *id)
>>   	if (asciihexlen & 1)
>>   		return ERR_PTR(-EINVAL);
>>   
>> -	match_id = kmalloc(sizeof(struct asymmetric_key_id) + asciihexlen / 2,
>> +	match_id = kmalloc(struct_size(match_id, data, asciihexlen / 2),
>>   			   GFP_KERNEL);
>>   	if (!match_id)
>>   		return ERR_PTR(-ENOMEM);
>> -- 
>> 2.36.0
>>
> .

Thanks for the review Gustavo.

I'll send a v3 patch and update the commit message. Maybe refer to the 
mail from Linus instead.

-- 
Best
GUO Zihua