Re: [PATCH net] selftests: net: csum: Fix checksums for packets with non-zero padding

[Willem de Bruijn <willemdebruijn.kernel@gmail.com>]

Eric Dumazet wrote:
> On Mon, Sep 9, 2024 at 5:02 PM Sean Anderson <sean.anderson@linux.dev> wrote:
> >
> > On 9/6/24 22:05, Willem de Bruijn wrote:
> > > Sean Anderson wrote:
> > >> Padding is not included in UDP and TCP checksums. Therefore, reduce the
> > >> length of the checksummed data to include only the data in the IP
> > >> payload. This fixes spurious reported checksum failures like
> > >>
> > >> rx: pkt: sport=33000 len=26 csum=0xc850 verify=0xf9fe
> > >> pkt: bad csum
> > >
> > > Are you using this test as receiver for other input?
> > >
> > > The packet builder in the test doesn't generate these, does it?
> >
> > It's added by the MAC before transmission.
> >
> > This is permitted by the standard, but in this case it actually appears
> > to be due to the MAC using 32-bit reads for the data and not masking off
> > the end. Not sure whether this is a bug in the driver/device, since
> > technically we may leak up to 3 bytes of memory.
> 
> This seems to be a bug in the driver.
> 
> A call to skb_put_padto(skb, ETH_ZLEN) should be added.

In which case this test detecting it may be nice to have, for lack of
a more targeted test.