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 <dp@highloadlab.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
index ef54377fb11cbdd3f327fa29c45c623923b8cb2f..397e0f69435fd1b1b4b3775cadc409d67ea63332 100644 (file)
--- 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);