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Date: Mon, 9 Oct 2023 14:33:01 -0600
From: "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To: Kees Cook <keescook@...omium.org>,
 "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc: Kalle Valo <kvalo@...nel.org>, linux-wireless@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] hostap: Add __counted_by for struct
 prism2_download_data and use struct_size()



On 10/9/23 21:54, Kees Cook wrote:
> On Mon, Oct 09, 2023 at 01:41:18PM -0600, Gustavo A. R. Silva wrote:
>> Prepare for the coming implementation by GCC and Clang of the __counted_by
>> attribute. Flexible array members annotated with __counted_by can have
>> their accesses bounds-checked at run-time via CONFIG_UBSAN_BOUNDS (for
>> array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
>> functions).
>>
>> While there, use struct_size() helper, instead of the open-coded
>> version, to calculate the size for the allocation of the whole
>> flexible structure, including of course, the flexible-array member.
>>
>> This code was found with the help of Coccinelle, and audited and
>> fixed manually.
>>
>> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
>> ---
>>   drivers/net/wireless/intersil/hostap/hostap_download.c | 3 +--
>>   drivers/net/wireless/intersil/hostap/hostap_wlan.h     | 2 +-
>>   2 files changed, 2 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/net/wireless/intersil/hostap/hostap_download.c b/drivers/net/wireless/intersil/hostap/hostap_download.c
>> index 3672291ced5c..5e5bada28b5b 100644
>> --- a/drivers/net/wireless/intersil/hostap/hostap_download.c
>> +++ b/drivers/net/wireless/intersil/hostap/hostap_download.c
>> @@ -732,8 +732,7 @@ static int prism2_download(local_info_t *local,
>>   		goto out;
>>   	}
>>   
>> -	dl = kzalloc(sizeof(*dl) + param->num_areas *
>> -		     sizeof(struct prism2_download_data_area), GFP_KERNEL);
>> +	dl = kzalloc(struct_size(dl, data, param->num_areas), GFP_KERNEL);
>>   	if (dl == NULL) {
>>   		ret = -ENOMEM;
>>   		goto out;
>> diff --git a/drivers/net/wireless/intersil/hostap/hostap_wlan.h b/drivers/net/wireless/intersil/hostap/hostap_wlan.h
>> index c25cd21d18bd..f71c0545c0be 100644
>> --- a/drivers/net/wireless/intersil/hostap/hostap_wlan.h
>> +++ b/drivers/net/wireless/intersil/hostap/hostap_wlan.h
>> @@ -617,7 +617,7 @@ struct prism2_download_data {
>>   		u32 addr; /* wlan card address */
>>   		u32 len;
>>   		u8 *data; /* allocated data */
>> -	} data[];
>> +	} data[] __counted_by(num_areas);
>>   };
> 
> Should this be considered a v2 of:
> https://lore.kernel.org/linux-hardening/94848cc3-6f5c-46d7-8cc7-98a4f10865b3@embeddedor.com/
> 
> ?

Oops... sorry, I forgot I had reviewed this patch of yours.

> 
> Yours is more complete since it includes the struct_size() change...
> 

Should I resend this explicitly marking it as a v2?

--
Gustavo

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