From ae2dd7164943e03644293af92802550d052632e6 Mon Sep 17 00:00:00 2001 From: Florian Westphal Date: Wed, 29 Jan 2020 15:54:46 +0100 Subject: mptcp: handle tcp fallback when using syn cookies We can't deal with syncookie mode yet, the syncookie rx path will create tcp reqsk, i.e. we get OOB access because we treat tcp reqsk as mptcp reqsk one: TCP: SYN flooding on port 20002. Sending cookies. BUG: KASAN: slab-out-of-bounds in subflow_syn_recv_sock+0x451/0x4d0 net/mptcp/subflow.c:191 Read of size 1 at addr ffff8881167bc148 by task syz-executor099/2120 subflow_syn_recv_sock+0x451/0x4d0 net/mptcp/subflow.c:191 tcp_get_cookie_sock+0xcf/0x520 net/ipv4/syncookies.c:209 cookie_v6_check+0x15a5/0x1e90 net/ipv6/syncookies.c:252 tcp_v6_cookie_check net/ipv6/tcp_ipv6.c:1123 [inline] [..] Bug can be reproduced via "sysctl net.ipv4.tcp_syncookies=2". Note that MPTCP should work with syncookies (4th ack would carry needed state), but it appears better to sort that out in -next so do tcp fallback for now. I removed the MPTCP ifdef for tcp_rsk "is_mptcp" member because if (IS_ENABLED()) is easier to read than "#ifdef IS_ENABLED()/#endif" pair. Cc: Eric Dumazet Fixes: cec37a6e41aae7bf ("mptcp: Handle MP_CAPABLE options for outgoing connections") Reported-by: Christoph Paasch Tested-by: Christoph Paasch Signed-off-by: Florian Westphal Signed-off-by: David S. Miller --- net/ipv4/tcp_input.c | 3 +++ 1 file changed, 3 insertions(+) (limited to 'net/ipv4/tcp_input.c') diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index e8b840a4767e..e325b4506e25 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -6637,6 +6637,9 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops, af_ops->init_req(req, sk, skb); + if (IS_ENABLED(CONFIG_MPTCP) && want_cookie) + tcp_rsk(req)->is_mptcp = 0; + if (security_inet_conn_request(sk, skb, req)) goto drop_and_free; -- cgit v1.2.3-59-g8ed1b