netinet6: Don't calculate offset on ICMP6 NI query if the copied mbuf is null

[nc]

Summary

netinet6: Don't calculate offset on ICMP6 NI query if the copied mbuf is null.

Submitted by: Neel Chauhan <neel AT neelc DOT org>

[donner]

I'd suggest to stop processing at this place.

sys/netinet6/icmp6.c

659

The handing of "n == NULL" is not consistent.
Instead of stop processing like below, some variables stay unset.

682–685

Here the "n == NULL" case is simple: stop processing.

723

If variables are still unset, prevent processing.

[hrs]

Adding the following two lines between the invocation of ni6_input() and the "nroff =" line is simpler. This noff line was added to suppress a "uninitialized variable" warning a long time ago, and the proposed change reverts it effectively while the code paths have no problem.

if (n)
        n = ni6_input(n, off);
if (n == NULL)
        break;
noff = sizeof(struct ip6_hdr);

[nc]

Good catch.

I'm not an expert in the kernel, sorry.