From 84b114b98452c431299d99c135f751659e517acb Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Fri, 5 May 2017 06:56:54 -0700 Subject: tcp: randomize timestamps on syncookies Whole point of randomization was to hide server uptime, but an attacker can simply start a syn flood and TCP generates 'old style' timestamps, directly revealing server jiffies value. Also, TSval sent by the server to a particular remote address vary depending on syncookies being sent or not, potentially triggering PAWS drops for innocent clients. Lets implement proper randomization, including for SYNcookies. Also we do not need to export sysctl_tcp_timestamps, since it is not used from a module. In v2, I added Florian feedback and contribution, adding tsoff to tcp_get_cookie_sock(). v3 removed one unused variable in tcp_v4_connect() as Florian spotted. Fixes: 95a22caee396c ("tcp: randomize tcp timestamp offsets for each connection") Signed-off-by: Eric Dumazet Reviewed-by: Florian Westphal Tested-by: Florian Westphal Cc: Yuchung Cheng Signed-off-by: David S. Miller --- net/ipv6/tcp_ipv6.c | 32 +++++++++++++++++++------------- 1 file changed, 19 insertions(+), 13 deletions(-) (limited to 'net/ipv6/tcp_ipv6.c') diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c index 8e42e8f54b70..aeb9497b5bb7 100644 --- a/net/ipv6/tcp_ipv6.c +++ b/net/ipv6/tcp_ipv6.c @@ -101,12 +101,18 @@ static void inet6_sk_rx_dst_set(struct sock *sk, const struct sk_buff *skb) } } -static u32 tcp_v6_init_seq_and_tsoff(const struct sk_buff *skb, u32 *tsoff) +static u32 tcp_v6_init_seq(const struct sk_buff *skb) { - return secure_tcpv6_seq_and_tsoff(ipv6_hdr(skb)->daddr.s6_addr32, - ipv6_hdr(skb)->saddr.s6_addr32, - tcp_hdr(skb)->dest, - tcp_hdr(skb)->source, tsoff); + return secure_tcpv6_seq(ipv6_hdr(skb)->daddr.s6_addr32, + ipv6_hdr(skb)->saddr.s6_addr32, + tcp_hdr(skb)->dest, + tcp_hdr(skb)->source); +} + +static u32 tcp_v6_init_ts_off(const struct sk_buff *skb) +{ + return secure_tcpv6_ts_off(ipv6_hdr(skb)->daddr.s6_addr32, + ipv6_hdr(skb)->saddr.s6_addr32); } static int tcp_v6_connect(struct sock *sk, struct sockaddr *uaddr, @@ -122,7 +128,6 @@ static int tcp_v6_connect(struct sock *sk, struct sockaddr *uaddr, struct flowi6 fl6; struct dst_entry *dst; int addr_type; - u32 seq; int err; struct inet_timewait_death_row *tcp_death_row = &sock_net(sk)->ipv4.tcp_death_row; @@ -282,13 +287,13 @@ static int tcp_v6_connect(struct sock *sk, struct sockaddr *uaddr, sk_set_txhash(sk); if (likely(!tp->repair)) { - seq = secure_tcpv6_seq_and_tsoff(np->saddr.s6_addr32, - sk->sk_v6_daddr.s6_addr32, - inet->inet_sport, - inet->inet_dport, - &tp->tsoffset); if (!tp->write_seq) - tp->write_seq = seq; + tp->write_seq = secure_tcpv6_seq(np->saddr.s6_addr32, + sk->sk_v6_daddr.s6_addr32, + inet->inet_sport, + inet->inet_dport); + tp->tsoffset = secure_tcpv6_ts_off(np->saddr.s6_addr32, + sk->sk_v6_daddr.s6_addr32); } if (tcp_fastopen_defer_connect(sk, &err)) @@ -749,7 +754,8 @@ static const struct tcp_request_sock_ops tcp_request_sock_ipv6_ops = { .cookie_init_seq = cookie_v6_init_sequence, #endif .route_req = tcp_v6_route_req, - .init_seq_tsoff = tcp_v6_init_seq_and_tsoff, + .init_seq = tcp_v6_init_seq, + .init_ts_off = tcp_v6_init_ts_off, .send_synack = tcp_v6_send_synack, }; -- cgit v1.2.3-59-g8ed1b