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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 <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;
}