Adds new tcp_timestamps=2 mode. If enabled, out-of-order segments
(within window but sequence number does not equal to rcv.next)
that carry data (i.e. pure acks are not tested) are also subject to a
check of tsecr, the timestamp echo value.
This make blind data injection more challenging if a connection is using
tcp timestamps as injected packet needs to match expected next sequence
number or carry a timestamp echo within an given range.
This approach could later be made more strict, f.e. this currently
uses tp->lsndtime which is only updated when we send data.
Because we only care about ofo segments, normal fastpath
(successful header prediction) is not changed. We also do not
send a challenge ack, as at least one packet is known to be in-flight
(or lost).
Signed-off-by: Florian Westphal <f...@strlen.de>
---
Documentation/networking/ip-sysctl.txt | 8 ++++++--
net/ipv4/tcp_input.c | 35 ++++++++++++++++++++++++++++++++++
2 files changed, 41 insertions(+), 2 deletions(-)
diff --git a/Documentation/networking/ip-sysctl.txt
b/Documentation/networking/ip-sysctl.txt
index 9ae9293..1e360a3 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -609,8 +609,12 @@ tcp_syn_retries - INTEGER
with the current initial RTO of 1second. With this the final timeout
for an active TCP connection attempt will happen after 127seconds.
-tcp_timestamps - BOOLEAN
- Enable timestamps as defined in RFC1323.
+tcp_timestamps - INTEGER
+ 0: Disabled.
+ 1: Enable timestamps as defined in RFC1323.
+ 2: Like 1, but also drop segments that arrive out-of-order if
+ their echo timestamp (TSecr) is outside of an expected range.
+ Default: 1
tcp_min_tso_segs - INTEGER
Minimal number of segments per TSO frame.
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 092f2dd..1234244 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -128,6 +128,8 @@ int sysctl_tcp_invalid_ratelimit __read_mostly = HZ/2;
#define REXMIT_LOST 1 /* retransmit packets marked lost */
#define REXMIT_NEW 2 /* FRTO-style transmit of unsent/new packets */
+#define TSECR_MAX_DELAY TCP_RTO_MAX
+
/* Adapt the MSS value used to make delayed ack decision to the
* real world.
*/
@@ -5165,6 +5167,30 @@ static int tcp_copy_to_iovec(struct sock *sk, struct
sk_buff *skb, int hlen)
return err;
}
+static bool tcp_validate_tsecr(struct sock *sk, const struct tcphdr *th)
+{
+ const struct tcp_sock *tp = tcp_sk(sk);
+ const struct sk_buff *skb = NULL;
+ u32 ts_low;
+
+ if (sysctl_tcp_timestamps != 2 || !tp->rx_opt.tstamp_ok)
+ return true;
+
+ /* packet has no timestamp but connection is supposed to */
+ if (!tp->rx_opt.saw_tstamp)
+ return false;
+
+ ts_low = tp->retrans_stamp;
+ if (ts_low == 0) {
+ skb = tcp_write_queue_head(sk);
+ ts_low = skb ? tcp_skb_timestamp(skb) : tp->lsndtime;
+ }
+
+ ts_low -= TSECR_MAX_DELAY;
+
+ return between(tp->rx_opt.rcv_tsecr, ts_low, tcp_time_stamp);
+}
+
/* Does PAWS and seqno based validation of an incoming segment, flags will
* play significant role here.
*/
@@ -5255,6 +5281,15 @@ syn_challenge:
goto discard;
}
+ if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt ||
+ TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq)
+ return true;
+
+ /* last step: ofo and not pure ack: check tsecr */
+ if (!tcp_validate_tsecr(sk, th)) {
+ goto discard;
+ }
+
return true;
discard:
--
2.7.3
