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

[Willem de Bruijn]

Jakub Kicinski wrote:
> On Mon, 09 Sep 2024 13:26:42 -0400 Willem de Bruijn wrote:
> > > 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.
> 
> IIUC we're basically saying that we don't need to trim because pad
> should be 0? In that case maybe let's keep the patch but add a check 
> on top which scans the pad for non-zero bytes, and print an informative
> warning?

Data arriving with padding probably deserves a separate test.

We can use this csum test as stand-in, I suppose.

Is it safe to assume that all padding is wrong on ingress, not just
non-zero padding. The ip stack itself treats it as benign and trims
the trailing bytes silently.

I do know of legitimate cases of trailer data lifting along.