On Fri, May 18, 2018 at 2:44 PM, Willem de Bruijn <willemdebruijn.ker...@gmail.com> wrote: > On Fri, May 18, 2018 at 1:09 PM, Willem de Bruijn > <willemdebruijn.ker...@gmail.com> wrote: >> On Fri, May 18, 2018 at 11:44 AM, David Miller <da...@davemloft.net> wrote: >>> From: Eric Dumazet <eric.duma...@gmail.com> >>> Date: Fri, 18 May 2018 08:30:43 -0700 >>> >>>> We probably need to revert Willem patch >>>> (7ce875e5ecb8562fd44040f69bda96c999e38bbc) >>> >>> Is it really valid to reach ip_recv_err with an ipv6 socket? >> >> I guess the issue is that setsockopt IPV6_ADDRFORM is not an >> atomic operation, so that the socket is neither fully ipv4 nor fully >> ipv6 by the time it reaches ip_recv_error. >> >> sk->sk_socket->ops = &inet_dgram_ops; >> < HERE > >> sk->sk_family = PF_INET; >> >> Even calling inet_recv_error to demux would not necessarily help. >> >> Safest would be to look up by skb->protocol, similar to what >> ipv6_recv_error does to handle v4-mapped-v6. >> >> Or to make that function safe with PF_INET and swap the order >> of the above two operations. >> >> All sound needlessly complicated for this rare socket option, but >> I don't have a better idea yet. Dropping on the floor is not nice, >> either. > > Ensuring that ip_recv_error correctly handles packets from either > socket and removing the warning should indeed be good. > > It is robust against v4-mapped packets from an AF_INET6 socket, > but see caveat on reconnect below. > > The code between ipv6_recv_error for v4-mapped addresses and > ip_recv_error is essentially the same, the main difference being > whether to return network headers as sockaddr_in with SOL_IP > or sockaddr_in6 with SOL_IPV6. > > There are very few other locations in the stack that explicitly test > sk_family in this way and thus would be vulnerable to races with > IPV6_ADDRFORM. > > I'm not sure whether it is possible for a udpv6 socket to queue a > real ipv6 packet on the error queue, disconnect, connect to an > ipv4 address, call IPV6_ADDRFORM and then call ip_recv_error > on a true ipv6 packet. That would return buggy data, e.g., in > msg_name.
In do_ipv6_setsockopt IPV6_ADDRFORM we can test that the error queue is empty, and then take its lock for the duration of the operation.
