Re: [PATCH v2] netfilter: ebtables: fix fortify warnings

[GONG, Ruiqi]

On 2023/08/09 6:53, Kees Cook wrote:
> 
> [...]
>>>
>>> diff --git a/include/uapi/linux/netfilter_bridge/ebtables.h b/include/uapi/linux/netfilter_bridge/ebtables.h
>>> index a494cf43a755..b0caad82b693 100644
>>> --- a/include/uapi/linux/netfilter_bridge/ebtables.h
>>> +++ b/include/uapi/linux/netfilter_bridge/ebtables.h
>>> @@ -182,12 +182,14 @@ struct ebt_entry {
>>>  	unsigned char sourcemsk[ETH_ALEN];
>>>  	unsigned char destmac[ETH_ALEN];
>>>  	unsigned char destmsk[ETH_ALEN];
>>> -	/* sizeof ebt_entry + matches */
>>> -	unsigned int watchers_offset;
>>> -	/* sizeof ebt_entry + matches + watchers */
>>> -	unsigned int target_offset;
>>> -	/* sizeof ebt_entry + matches + watchers + target */
>>> -	unsigned int next_offset;
>>> +	__struct_group(/* no tag */, offsets, /* no attrs */,
>>> +		/* sizeof ebt_entry + matches */
>>> +		unsigned int watchers_offset;
>>> +		/* sizeof ebt_entry + matches + watchers */
>>> +		unsigned int target_offset;
>>> +		/* sizeof ebt_entry + matches + watchers + target */
>>> +		unsigned int next_offset;
>>> +	);
>>>  	unsigned char elems[0] __attribute__ ((aligned (__alignof__(struct ebt_replace))));
> 
> While we're here, can we drop this [0] in favor of []?
> 
> -Kees
> 

There are still quite a lot of zero-element array in
include/uapi/linux/netfilter_bridge/ebtables.h. I will submit another
patch to change them altogether.

>>>  };
>>>  
>>> diff --git a/net/bridge/netfilter/ebtables.c b/net/bridge/netfilter/ebtables.c
>>> index 757ec46fc45a..5ec66b1ebb64 100644
>>> --- a/net/bridge/netfilter/ebtables.c
>>> +++ b/net/bridge/netfilter/ebtables.c
>>> @@ -2115,8 +2115,7 @@ static int size_entry_mwt(const struct ebt_entry *entry, const unsigned char *ba
>>>  		return ret;
>>>  
>>>  	offsets[0] = sizeof(struct ebt_entry); /* matches come first */
>>> -	memcpy(&offsets[1], &entry->watchers_offset,
>>> -			sizeof(offsets) - sizeof(offsets[0]));
>>> +	memcpy(&offsets[1], &entry->offsets, sizeof(offsets) - sizeof(offsets[0]));
>> 							^^^^^^^^^^^^
>> You now can replace this ____________________________________|
>> with just `sizeof(entry->offsets)`
>>
>> With that change you can add my
>> Reviewed-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>
>>
>> Thank you
>> --
>> Gustavo
>>
>>>  
>>>  	if (state->buf_kern_start) {
>>>  		buf_start = state->buf_kern_start + state->buf_kern_offset;
>>> -- 
>>> 2.41.0
>>>
> 
>