Re: [dpdk-dev] [PATCH v2 1/3] net/af_packet: set_mtu() decrements sockaddr twice

["Lam, Tiago" <tiago.lam@intel.com>]

On 20/11/2018 10:29, Kevin Traynor wrote:
> On 11/20/2018 10:26 AM, Tiago Lam wrote:
>> When setting the MTU, eth_dev_mtu_set() is called to validate the
>> provided MTU. As part of that, it calculates the useful area to store
>> data and compares it against the MTU, to guarantee that there's enough
>> space to store the data. It calculates that as:
>>     "tp_frame_size - TPACKET2_HDRLEN - sizeof(struct sockaddr_ll)"
>>
>> However, the TPACKET2_HDRLEN macro already increaments sizeof(struct
>> sockaddr_ll) internally, meaning the useuful area of data above will
>> have sizeof(struct sockaddr_ll) decremented twice.
>>
>> Instead, the useful area of data should be calculated as:
>>     "tp_frame_size - TPACKET2_HDRLEN"
>>
>> This makes sure that there's enough useful area to fit the provided MTU
>> after excluding tpacket2_hdr and sockaddr_ll.
>>
>> Fixes: cc68ac4 ("net/af_packet: support MTU change")
>>
> 
> It should be for stable also?

Indeed, thanks for pointing that out. I've missed the Cc there, but it
should be backported - I can track it down to 17.02. I'll make sure I
add the Cc if a new iteration is needed.

Tiago.

> 
>> Signed-off-by: Tiago Lam <tiago.lam@intel.com>
>> ---
>>  drivers/net/af_packet/rte_eth_af_packet.c | 3 +--
>>  1 file changed, 1 insertion(+), 2 deletions(-)
>>
>> diff --git a/drivers/net/af_packet/rte_eth_af_packet.c b/drivers/net/af_packet/rte_eth_af_packet.c
>> index 95a98c6..264cfc0 100644
>> --- a/drivers/net/af_packet/rte_eth_af_packet.c
>> +++ b/drivers/net/af_packet/rte_eth_af_packet.c
>> @@ -433,8 +433,7 @@ eth_dev_mtu_set(struct rte_eth_dev *dev, uint16_t mtu)
>>  	int ret;
>>  	int s;
>>  	unsigned int data_size = internals->req.tp_frame_size -
>> -				 TPACKET2_HDRLEN -
>> -				 sizeof(struct sockaddr_ll);
>> +				 TPACKET2_HDRLEN;
>>  
>>  	if (mtu > data_size)
>>  		return -EINVAL;
>>
>