Re: [PATCH] netfilter: nf_tables: check if payload offset is a power of 2

[Nikolay Aleksandrov <nikolay@redhat.com>]

On 02/16/2014 01:07 PM, Patrick McHardy wrote:
> On Sun, Feb 16, 2014 at 12:54:40PM +0100, Nikolay Aleksandrov wrote:
>> Add a check if payload's offset is a power of 2 when selecting ops.
>> The fast ops were meant for well aligned offsets, also this fixes a
>> small bug when using unaligned offset and length of 3 which causes
>> only 1 byte to be loaded because the fast ops are chosen.
>>
>> Signed-off-by: Nikolay Aleksandrov <nikolay@redhat.com>
>> ---
>> I broke the line since it was >80 chars.
>> This patch applies to Dave's -net tree.
>>
>>  net/netfilter/nft_payload.c | 4 +++-
>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/net/netfilter/nft_payload.c b/net/netfilter/nft_payload.c
>> index a2aeb31..15a3dcb 100644
>> --- a/net/netfilter/nft_payload.c
>> +++ b/net/netfilter/nft_payload.c
>> @@ -135,7 +135,9 @@ nft_payload_select_ops(const struct nft_ctx *ctx,
>>  	if (len == 0 || len > FIELD_SIZEOF(struct nft_data, data))
>>  		return ERR_PTR(-EINVAL);
>>  
>> -	if (len <= 4 && IS_ALIGNED(offset, len) && base != NFT_PAYLOAD_LL_HEADER)
>> +	if (len <= 4 && IS_ALIGNED(offset, len) &&
>> +	    base != NFT_PAYLOAD_LL_HEADER &&
>> +	    !(offset & (offset - 1)))
> 
> Small cosmetic note: we have is_power_of_2(), which does exactly this.
> 
I didn't choose is_power_of_2 because it also checks if x is != 0, so I
thought we can allow for 0 offset with the fast ops.

> Also I think the more logical order would be:
> 
> len <= 4 && is_power_of_2 && IS_ALIGNED && base ...
> 
Okay :-)

>>  		return &nft_payload_fast_ops;
>>  	else
>>  		return &nft_payload_ops;
>> -- 
>> 1.8.4.2