On Mon, 2021-06-28 at 12:27 +0800, Jason Wang wrote:

quoted

If we're going to continue to *not* check on the XDP path, we similarly
need a proof that it can't be fragmented. And also a reason to bother
with the "optimisation", of course.

For XDP path, we simply need to add a length check since the packet is 
always a linear memory.

Sure, but in that case skb_headlen is going to be enough to cover
ETH_HLEN, and that's the very first thing that the standard inline
version of pskb_may_pull() checks, without ever even having to make an
out-of-line call.

So there's just no reason ever for us *not* to keep it really simple,
and use pskb_may_pull() in all cases.