[097/118] tcp: call tcp_replace_ts_recent() from tcp_ack()

Ben Hutchings
2013-05-10T14:45:41Z

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 12fb3dd9dc3c64ba7d64cec977cca9b5fb7b1d4e ]

commit bd090dfc634d (tcp: tcp_replace_ts_recent() should not be called
from tcp_validate_incoming()) introduced a TS ecr bug in slow path
processing.

1 A > B P. 1:10001(10000) ack 1 <nop,nop,TS val 1001 ecr 200>
2 B < A . 1:1(0) ack 1 win 257 <sack 9001:10001,TS val 300 ecr 1001>
3 A > B . 1:1001(1000) ack 1 win 227 <nop,nop,TS val 1002 ecr 200>
4 A > B . 1001:2001(1000) ack 1 win 227 <nop,nop,TS val 1002 ecr 200>

(ecr 200 should be ecr 300 in packets 3 & 4)

Problem is tcp_ack() can trigger send of new packets (retransmits),
reflecting the prior TSval, instead of the TSval contained in the
currently processed incoming packet.

Fix this by calling tcp_replace_ts_recent() from tcp_ack() after the
checks, but before the actions.

Reported-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
net/ipv4/tcp_input.c | 65 ++++++++++++++++++++++++++--------------------------
1 file changed, 32 insertions(+), 33 deletions(-)

--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -115,6 +115,7 @@ int sysctl_tcp_abc __read_mostly;
#define FLAG_DSACKING_ACK 0x800 /* SACK blocks contained D-SACK info */
#define FLAG_NONHEAD_RETRANS_ACKED 0x1000 /* Non-head rexmitted data was ACKed */
#define FLAG_SACK_RENEGING 0x2000 /* snd_una advanced to a sacked seq */
+#define FLAG_UPDATE_TS_RECENT 0x4000 /* tcp_replace_ts_recent() */

#define FLAG_ACKED (FLAG_DATA_ACKED|FLAG_SYN_ACKED)
#define FLAG_NOT_DUP (FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
@@ -3723,6 +3724,27 @@ static void tcp_send_challenge_ack(struc
}
}

+static void tcp_store_ts_recent(struct tcp_sock *tp)
+{
+ tp->rx_opt.ts_recent = tp->rx_opt.rcv_tsval;
+ tp->rx_opt.ts_recent_stamp = get_seconds();
+}
+
+static void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq)
+{
+ if (tp->rx_opt.saw_tstamp && !after(seq, tp->rcv_wup)) {
+ /* PAWS bug workaround wrt. ACK frames, the PAWS discard
+ * extra check below makes sure this can only happen
+ * for pure ACK frames. -DaveM
+ *
+ * Not only, also it occurs for expired timestamps.
+ */
+
+ if (tcp_paws_check(&tp->rx_opt, 0))
+ tcp_store_ts_recent(tp);
+ }
+}
+
/* This routine deals with incoming acks, but not outgoing ones. */
static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
{
@@ -3771,6 +3793,12 @@ static int tcp_ack(struct sock *sk, cons
prior_fackets = tp->fackets_out;
prior_in_flight = tcp_packets_in_flight(tp);

+ /* ts_recent update must be made after we are sure that the packet
+ * is in window.
+ */
+ if (flag & FLAG_UPDATE_TS_RECENT)
+ tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
+
if (!(flag & FLAG_SLOWPATH) && after(ack, prior_snd_una)) {
/* Window is constant, pure forward advance.
* No more checks are required.
@@ -4061,27 +4089,6 @@ const u8 *tcp_parse_md5sig_option(const
EXPORT_SYMBOL(tcp_parse_md5sig_option);
#endif

-static inline void tcp_store_ts_recent(struct tcp_sock *tp)
-{
- tp->rx_opt.ts_recent = tp->rx_opt.rcv_tsval;
- tp->rx_opt.ts_recent_stamp = get_seconds();
-}
-
-static inline void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq)
-{
- if (tp->rx_opt.saw_tstamp && !after(seq, tp->rcv_wup)) {
- /* PAWS bug workaround wrt. ACK frames, the PAWS discard
- * extra check below makes sure this can only happen
- * for pure ACK frames. -DaveM
- *
- * Not only, also it occurs for expired timestamps.
- */
-
- if (tcp_paws_check(&tp->rx_opt, 0))
- tcp_store_ts_recent(tp);
- }
-}
-
/* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM
*
* It is not fatal. If this ACK does _not_ change critical state (seqs, window)
@@ -5552,14 +5559,10 @@ slow_path:
return 0;

step5:
- if (th->ack && tcp_ack(sk, skb, FLAG_SLOWPATH) < 0)
+ if (th->ack &&
+ tcp_ack(sk, skb, FLAG_SLOWPATH | FLAG_UPDATE_TS_RECENT) < 0)
goto discard;

- /* ts_recent update must be made after we are sure that the packet
- * is in window.
- */
- tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
-
tcp_rcv_rtt_measure_ts(sk, skb);

/* Process urgent data. */
@@ -5923,7 +5926,8 @@ int tcp_rcv_state_process(struct sock *s

/* step 5: check the ACK field */
if (th->ack) {
- int acceptable = tcp_ack(sk, skb, FLAG_SLOWPATH) > 0;
+ int acceptable = tcp_ack(sk, skb, FLAG_SLOWPATH |
+ FLAG_UPDATE_TS_RECENT) > 0;

switch (sk->sk_state) {
case TCP_SYN_RECV:
@@ -6030,11 +6034,6 @@ int tcp_rcv_state_process(struct sock *s
} else
goto discard;

- /* ts_recent update must be made after we are sure that the packet
- * is in window.
- */
- tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
-
/* step 6: check the URG bit */
tcp_urg(sk, skb, th);