If a sk_v6_rcv_saddr is !IPV6_ADDR_ANY and !IPV6_ADDR_MAPPED, it
implicitly implies it is an ipv6only socket. However, in inet6_bind(),
this addr_type checking and setting sk->sk_ipv6only to 1 are only done
after sk->sk_prot->get_port(sk, snum) has been completed successfully.
This inconsistency between sk_v6_rcv_saddr and sk_ipv6only confuses
the 'get_port()'.
In particular, when binding SO_REUSEPORT UDP sockets,
udp_reuseport_add_sock(sk,...) is called. udp_reuseport_add_sock()
checks "ipv6_only_sock(sk2) == ipv6_only_sock(sk)" before adding sk to
sk2->sk_reuseport_cb. In this case, ipv6_only_sock(sk2) could be
1 while ipv6_only_sock(sk) is still 0 here. The end result is,
reuseport_alloc(sk) is called instead of adding sk to the existing
sk2->sk_reuseport_cb.
It can be reproduced by binding two SO_REUSEPORT UDP sockets on an
IPv6 address (!ANY and !MAPPED). Only one of the socket will
receive packet.
The fix is to set the implicit sk_ipv6only before calling get_port().
The original sk_ipv6only has to be saved such that it can be restored
in case get_port() failed. The situation is similar to the
inet_reset_saddr(sk) after get_port() has failed.
Thanks to Calvin Owens <calvinowens@fb.com> who created an easy
reproduction which leads to a fix.
Fixes: e32ea7e747 ("soreuseport: fast reuseport UDP socket selection")
Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
7ece54a60e