netinet: Explicitly disallow connections to the unspecified address

[markj]

Summary

If the V_connect_ifaddr_wild sysctl says that we shouldn't infer a
destination address, return an error. Otherwise it's possible for use
of an unspecified foreign address to trigger a subsequent assertion
failure, for example in in_pcblookup_hash_locked().

Reported by: Shawn Webb <[e-mail]>

[emaste]

What if V_connect_inaddr_wild is true but also CK_STAILQ_EMPTY(&V_in_ifaddrhead)?
I guess ENETUNREACH is sensible in that case as well.

[markj]

In D46454#1058928, @emaste wrote:

What if V_connect_inaddr_wild is true but also CK_STAILQ_EMPTY(&V_in_ifaddrhead)?
I guess ENETUNREACH is sensible in that case as well.

Yes, that was intentional. This is really about ensuring that the unspecified address, which is used as a sentinel in some places, doesn't get propagated further down into the inpcb layer.

[zlei]

Looks good to me.