2013-04-11 18:55:14

by Dmitry Popov

Subject: [PATCH RESEND] tcp: incoming connections might use wrong route under synflood

There is a bug in cookie_v4_check (net/ipv4/syncookies.c):
flowi4_init_output(&fl4, 0, sk->sk_mark, RT_CONN_FLAGS(sk),
RT_SCOPE_UNIVERSE, IPPROTO_TCP,
inet_sk_flowi_flags(sk),
(opt && opt->srr) ? opt->faddr : ireq->rmt_addr,
ireq->loc_addr, th->source, th->dest);

Here we do not respect sk->sk_bound_dev_if, therefore wrong dst_entry may be
taken. This dst_entry is used by new socket (get_cookie_sock ->
tcp_v4_syn_recv_sock), so its packets may take the wrong path.

Signed-off-by: Dmitry Popov <[email protected]>
---
net/ipv4/syncookies.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
index ef54377..397e0f6 100644
--- a/net/ipv4/syncookies.c
+++ b/net/ipv4/syncookies.c
@@ -349,8 +349,8 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb,
* hasn't changed since we received the original syn, but I see
* no easy way to do this.
*/
- flowi4_init_output(&fl4, 0, sk->sk_mark, RT_CONN_FLAGS(sk),
- RT_SCOPE_UNIVERSE, IPPROTO_TCP,
+ flowi4_init_output(&fl4, sk->sk_bound_dev_if, sk->sk_mark,
+ RT_CONN_FLAGS(sk), RT_SCOPE_UNIVERSE, IPPROTO_TCP,
inet_sk_flowi_flags(sk),
(opt && opt->srr) ? opt->faddr : ireq->rmt_addr,
ireq->loc_addr, th->source, th->dest);

2013-04-11 20:02:39

by David Miller

Subject: Re: [PATCH RESEND] tcp: incoming connections might use wrong route under synflood

From: Dmitry Popov <[email protected]>
Date: Thu, 11 Apr 2013 22:55:07 +0400

> There is a bug in cookie_v4_check (net/ipv4/syncookies.c):
> flowi4_init_output(&fl4, 0, sk->sk_mark, RT_CONN_FLAGS(sk),
> RT_SCOPE_UNIVERSE, IPPROTO_TCP,
> inet_sk_flowi_flags(sk),
> (opt && opt->srr) ? opt->faddr : ireq->rmt_addr,
> ireq->loc_addr, th->source, th->dest);
>
> Here we do not respect sk->sk_bound_dev_if, therefore wrong dst_entry may be
> taken. This dst_entry is used by new socket (get_cookie_sock ->
> tcp_v4_syn_recv_sock), so its packets may take the wrong path.
>
> Signed-off-by: Dmitry Popov <[email protected]>

Applied.