Problem with checksum offloading on RPi3 (PF + Jails involved)

[YongHyeon PYUN]

On Wed, Nov 18, 2020 at 10:47:08AM +0100, Carsten Bäcker wrote:

[...]

> Sorry, that's my fault - i overlooked your request for a test with pf
> enabled.
> The example-ruleset is attached again. I added a line to allow the
> incoming ping to 5555.
> 
> I don't see a difference until i enable the redirection to the jail
> which makes the packet with extended data-length fail.
> Once i disable RXCSUM it works.
> 

Thanks for testing.  Unfortunately I couldn't find a driver issue
on patched smsc(4).  Quick looking pf(4) makes me wonder how it
verifies UDP datagrams.

Kristof, does pf(4) take advantage of H/W checksummed result for
UDP datagrams?  It seems pf_check_proto_cksum() always pass
IPPROTO_TCP such that UDP pseudo checksum is not computed in the
function.  I'm under the impression that incremental checksum
update for UDP datagrams with only CSUM_DATA_VALID bit wouldn't
work.