Re: [PATCH v2 net-next 2/6] udp: Constify skb argument in lookup functions

From: Tom Herbert <redacted>
Date: Tue, 29 Aug 2017 16:27:07 -0700

For UDP socket lookup functions, and associateed functions that take an
skbuf as argument, declare the skb argument as constant.

One caveat is that reuseport_select_sock can be called from the UDP
lookup functions with an skb argument. This function temporarily
modifies the skbuff data pointer (in bpf_run via a pull/push sequence).
To resolve compiler warning I added a local skbuf declaration that is
not const and assigned to the skb argument with an explicit cast.

Signed-off-by: Tom Herbert <redacted>

Please don't do this.

If reuseport_select_sock() modifies anything in the SKB, especially
skb->data, it infects the entire call chain.  So you can't mark it
const in this family of calls.