diff options
authorHannes Frederic Sowa <hannes@stressinduktion.org>2014-08-14 22:06:12 +0200
committerDavid S. Miller <davem@davemloft.net>2014-08-14 14:38:54 -0700
commita26552afe89438eefbe097512b3187f2c7e929fd (patch)
parent4fab9071950c2021d846e18351e0f46a1cffd67b (diff)
tcp: don't allow syn packets without timestamps to pass tcp_tw_recycle logic
tcp_tw_recycle heavily relies on tcp timestamps to build a per-host ordering of incoming connections and teardowns without the need to hold state on a specific quadruple for TCP_TIMEWAIT_LEN, but only for the last measured RTO. To do so, we keep the last seen timestamp in a per-host indexed data structure and verify if the incoming timestamp in a connection request is strictly greater than the saved one during last connection teardown. Thus we can verify later on that no old data packets will be accepted by the new connection. During moving a socket to time-wait state we already verify if timestamps where seen on a connection. Only if that was the case we let the time-wait socket expire after the RTO, otherwise normal TCP_TIMEWAIT_LEN will be used. But we don't verify this on incoming SYN packets. If a connection teardown was less than TCP_PAWS_MSL seconds in the past we cannot guarantee to not accept data packets from an old connection if no timestamps are present. We should drop this SYN packet. This patch closes this loophole. Please note, this patch does not make tcp_tw_recycle in any way more usable but only adds another safety check: Sporadic drops of SYN packets because of reordering in the network or in the socket backlog queues can happen. Users behing NAT trying to connect to a tcp_tw_recycle enabled server can get caught in blackholes and their connection requests may regullary get dropped because hosts behind an address translator don't have synchronized tcp timestamp clocks. tcp_tw_recycle cannot work if peers don't have tcp timestamps enabled. In general, use of tcp_tw_recycle is disadvised. Cc: Eric Dumazet <eric.dumazet@gmail.com> Cc: Florian Westphal <fw@strlen.de> Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org> Signed-off-by: David S. Miller <davem@davemloft.net>
3 files changed, 11 insertions, 6 deletions
diff --git a/include/net/tcp.h b/include/net/tcp.h
index e337e05035b..590e01a476a 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -417,7 +417,7 @@ void tcp_update_metrics(struct sock *sk);
void tcp_init_metrics(struct sock *sk);
void tcp_metrics_init(void);
bool tcp_peer_is_proven(struct request_sock *req, struct dst_entry *dst,
- bool paws_check);
+ bool paws_check, bool timestamps);
bool tcp_remember_stamp(struct sock *sk);
bool tcp_tw_remember_stamp(struct inet_timewait_sock *tw);
void tcp_fetch_timewait_stamp(struct sock *sk, struct dst_entry *dst);
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 1a8e89fdd33..4f6cfbc5777 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -5979,12 +5979,14 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
* timewait bucket, so that all the necessary checks
* are made in the function processing timewait state.
- if (tmp_opt.saw_tstamp && tcp_death_row.sysctl_tw_recycle) {
+ if (tcp_death_row.sysctl_tw_recycle) {
bool strict;
dst = af_ops->route_req(sk, &fl, req, &strict);
if (dst && strict &&
- !tcp_peer_is_proven(req, dst, true)) {
+ !tcp_peer_is_proven(req, dst, true,
+ tmp_opt.saw_tstamp)) {
goto drop_and_release;
@@ -5993,7 +5995,8 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
else if (!sysctl_tcp_syncookies &&
(sysctl_max_syn_backlog - inet_csk_reqsk_queue_len(sk) <
(sysctl_max_syn_backlog >> 2)) &&
- !tcp_peer_is_proven(req, dst, false)) {
+ !tcp_peer_is_proven(req, dst, false,
+ tmp_opt.saw_tstamp)) {
/* Without syncookies last quarter of
* backlog is filled with destinations,
* proven to be alive.
diff --git a/net/ipv4/tcp_metrics.c b/net/ipv4/tcp_metrics.c
index 0d54e59b9ea..ed9c9a91851 100644
--- a/net/ipv4/tcp_metrics.c
+++ b/net/ipv4/tcp_metrics.c
@@ -576,7 +576,8 @@ reset:
tp->snd_cwnd_stamp = tcp_time_stamp;
-bool tcp_peer_is_proven(struct request_sock *req, struct dst_entry *dst, bool paws_check)
+bool tcp_peer_is_proven(struct request_sock *req, struct dst_entry *dst,
+ bool paws_check, bool timestamps)
struct tcp_metrics_block *tm;
bool ret;
@@ -589,7 +590,8 @@ bool tcp_peer_is_proven(struct request_sock *req, struct dst_entry *dst, bool pa
if (paws_check) {
if (tm &&
(u32)get_seconds() - tm->tcpm_ts_stamp < TCP_PAWS_MSL &&
- (s32)(tm->tcpm_ts - req->ts_recent) > TCP_PAWS_WINDOW)
+ ((s32)(tm->tcpm_ts - req->ts_recent) > TCP_PAWS_WINDOW ||
+ !timestamps))
ret = false;
ret = true;