rtsock: fix buffer overrun (sockaddr misuse)

[takahiro.kurosawa_gmail.com]

Summary

struct sockaddr is not sufficient for buffer that can hold any
sockaddr_* structure. struct sockaddr_storage should be used.

Test Plan

ifconfig epair create
ifconfig epair0a inet6 add 2001:db8::1 up
ndp -s 2001:db8::2 02:86:98:2e:96:0b proxy # this triggers kernel stack overflow

[kp]

Good catch!

sys/net/rtsock.c

808

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