Problem using AF_PACKET with SOCK_RAW on ieee802514 devices

[Josef Filzmaier <j.filzmaier@gmx.at>]

Hello everyone (again)!

I am using the linux-wpan stack with the atusb and at86rf230 drivers (rf212).
Moreover i am using raw sockets to test some userspace implemenation of a 
custom protocol. In userspace i am using (attention, golang ahead)

> protocol = htons(syscall.ETH_P_IEEE802154)
> syscall.Socket(syscall.AF_PACKET, syscall.SOCK_RAW, int(protocol))

to create a raw socket. This has been working as desired up until commit 
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?
id=b84bbaf7a6c8cca24f8acf25a2c8e46913a947ba

After this commit the kernel mistakenly attaches two uninitialized bytes at 
the end of my raw data. I am currently using a patched kernel which uses the 
following code in af_packet.c (Modified the else if over Willem de Brujin's 
patch)

> } else if (sock->type != SOCK_RAW && reserve {
> 	skb_push(skb, reserve);
> }

Making this modification i can use my raw sockets with the correct length 
again. I wanted to ask if my solution is sensible here. I'm not 100% sure on 
why the patch was introduced, and my solution might not be sufficient for all 
use cases.

Another solution i thought of was to change the dev->hard_header_len but i'm 
unsure about changing these constants.

Is anyone else having this problem here, or can anyone else reproduce?
Any comments on whether my solution (or a modified one) could be upstreamed?

Thanks

-- 
Filzmaier Josef