Commit 12fb3dd9 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

tcp: call tcp_replace_ts_recent() from tcp_ack() 



commit bd090dfc (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: default avatarYuchung Cheng <ycheng@google.com>
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Acked-by: default avatarNeal Cardwell <ncardwell@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 4394542c

net/ipv4/tcp_input.c

+31 −33
Original line number Diff line number Diff line
@@ -113,6 +113,7 @@ int sysctl_tcp_early_retrans __read_mostly = 2; 
#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)
@@ -3564,6 +3565,27 @@ static void tcp_send_challenge_ack(struct sock *sk) 
	}

}



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)

{
@@ -3607,6 +3629,12 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag) 
	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.
@@ -3927,27 +3955,6 @@ const u8 *tcp_parse_md5sig_option(const struct tcphdr *th) 
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)
@@ -5543,14 +5550,9 @@ slow_path: 
		return 0;



step5:

	if (tcp_ack(sk, skb, FLAG_SLOWPATH) < 0)

	if (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. */
@@ -5986,7 +5988,8 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb, 


	/* step 5: check the ACK field */

	if (true) {

		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:
@@ -6137,11 +6140,6 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb, 
		}

	}



	/* 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);

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