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mptcp: handle tcp fallback when using syn cookies

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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 <edumazet@google.com>
Fixes: cec37a6e41 ("mptcp: Handle MP_CAPABLE options for outgoing connections")
Reported-by: Christoph Paasch <cpaasch@apple.com>
Tested-by: Christoph Paasch <cpaasch@apple.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Florian Westphal 2020-01-29 15:54:46 +01:00 committed by David S. Miller
parent b2c5b614ca
commit ae2dd71649
5 changed files with 14 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
include/linux/tcp.h
View File

@ -148,9 +148,7 @@ struct tcp_request_sock {
const struct tcp_request_sock_ops *af_specific;
u64 snt_synack; /* first SYNACK sent time */
bool tfo_listener;
#if IS_ENABLED(CONFIG_MPTCP)
bool is_mptcp;
#endif
u32 txhash;
u32 rcv_isn;
u32 snt_isn;

4
net/ipv4/syncookies.c
View File

@ -349,6 +349,10 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)
req->ts_recent = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsval : 0;
treq->snt_synack = 0;
treq->tfo_listener = false;
if (IS_ENABLED(CONFIG_MPTCP))
treq->is_mptcp = 0;
if (IS_ENABLED(CONFIG_SMC))
ireq->smc_ok = 0;

3
net/ipv4/tcp_input.c
View File

@ -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;

3
net/ipv6/syncookies.c
View File

@ -178,6 +178,9 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
treq = tcp_rsk(req);
treq->tfo_listener = false;
if (IS_ENABLED(CONFIG_MPTCP))
treq->is_mptcp = 0;
if (security_inet_conn_request(sk, skb, req))
goto out_free;

5
net/mptcp/subflow.c
View File

@ -186,6 +186,9 @@ static struct sock *subflow_syn_recv_sock(const struct sock *sk,
pr_debug("listener=%p, req=%p, conn=%p", listener, req, listener->conn);
if (tcp_rsk(req)->is_mptcp == 0)
goto create_child;
/* if the sk is MP_CAPABLE, we try to fetch the client key */
subflow_req = mptcp_subflow_rsk(req);
if (subflow_req->mp_capable) {
@ -769,7 +772,7 @@ static void subflow_ulp_clone(const struct request_sock *req,
struct mptcp_subflow_context *old_ctx = mptcp_subflow_ctx(newsk);
struct mptcp_subflow_context *new_ctx;
if (!subflow_req->mp_capable) {
if (!tcp_rsk(req)->is_mptcp || !subflow_req->mp_capable) {
subflow_ulp_fallback(newsk, old_ctx);
return;
}