[Bug 210726] tcp connect() can return invalid EADDRINUSE (Eg: multiple jails with the same IP address)

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=210726

--- Comment #26 from firk@cantconnect.ru ---
Created attachment 232948
  --> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=232948&action=edit
patch for 12.x 13.x 14-CURRENT

> connecting from an IPv6 address to an IPv4 one.

How do you connect from IPv6 to IPv4?
It giving me EINVAL (12.3) or EAFNOSUPPORT (14) when I try to call bind() or
connect() with IPv4 address on IPv6 socket.

And that's check at the very beginning of tcp6_usr_connect():

>        if (nam->sa_family != AF_INET6)
>                return (EAFNOSUPPORT);
>        if (nam->sa_len != sizeof (*sin6))
>                return (EINVAL);

giving no chance to handle IPv4 address with it.

Do you using jails? I found a way to still trigger EADDRINUSE from connect()
from a jail in 12.3 and 14-CURRENT, may be that's your case:
bind(fd,{0.0.0.0:0}) and then do connect (that's all for a pure IPv4 socket).

Since the issue you linked contains "connect from wildcard IPv6", most likely
it was really wildcard-bound IPv4 (because connecting from IPv6 to IPv4 is not
possible at all).

Adding a patch to fix that (that's the same patch that was posted 6 years ago
but very slightly modified for freebsd 12+).

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