This patch allows the sender to distinguish original and retransmitted packets.
That is in particular needed for the retransmission of Request packets, since
* the first packet uses ISS (generated in net/dccp/ipv?.c), and sets GSS = ISS;
* all retransmitted packets use GSS' = GSS + 1, so that the n-th retransmitted
packet has sequence number ISS + n (mod 48).
To add this support, the patch reorganises existing code in such a manner that
* icsk_retransmits == 0 for the original packet and
* icsk_retransmits = n > 0 for the n-th retransmitted packet
at the time dccp_transmit_skb() is called via dccp_retransmit_skb().
This patch is thanks to Wei Yongjun, who pointed this problem out, and to
Arnaldo for further discussion.
Further changes:
----------------
* exploits that, since sk_send_head always contains the original skb (enqueued
by dccp_entail()), skb_cloned() never evaluated to true;
* removed the `skb' argument from dccp_retransmit_skb(), since sk_send_head
is used for all retransmissions (the exception is client-Acks in PARTOPEN
state, but these are not put onto the sk_send_head);
* updated documentation.
Signed-off-by: Gerrit Renker <gerrit@xxxxxxxxxxxxxx>
---
net/dccp/dccp.h | 2 +-
net/dccp/output.c | 20 ++++++++++++++++----
net/dccp/timer.c | 20 ++++----------------
3 files changed, 21 insertions(+), 21 deletions(-)
--- a/net/dccp/dccp.h
+++ b/net/dccp/dccp.h
@@ -226,7 +226,7 @@ static inline void dccp_csum_outgoing(struct sk_buff *skb)
extern void dccp_v4_send_check(struct sock *sk, int len, struct sk_buff *skb);
-extern int dccp_retransmit_skb(struct sock *sk, struct sk_buff *skb);
+extern int dccp_retransmit_skb(struct sock *sk);
extern void dccp_send_ack(struct sock *sk);
extern void dccp_reqsk_send_ack(struct sk_buff *sk, struct request_sock *rsk);
--- a/net/dccp/output.c
+++ b/net/dccp/output.c
@@ -284,14 +284,26 @@ void dccp_write_xmit(struct sock *sk, int block)
}
}
-int dccp_retransmit_skb(struct sock *sk, struct sk_buff *skb)
+/**
+ * dccp_retransmit_skb - Retransmit Request, Close, or CloseReq packets
+ * There are only four retransmittable packet types in DCCP:
+ * - Request in client-REQUEST state (sec. 8.1.1),
+ * - CloseReq in server-CLOSEREQ state (sec. 8.3),
+ * - Close in node-CLOSING state (sec. 8.3),
+ * - Acks in client-PARTOPEN state (sec. 8.1.5, handled by dccp_delack_timer()).
+ * This function expects sk->sk_send_head to contain the original skb.
+ */
+int dccp_retransmit_skb(struct sock *sk)
{
+ BUG_TRAP(sk->sk_send_head != NULL);
+
if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk) != 0)
return -EHOSTUNREACH; /* Routing failure or similar. */
- return dccp_transmit_skb(sk, (skb_cloned(skb) ?
- pskb_copy(skb, GFP_ATOMIC):
- skb_clone(skb, GFP_ATOMIC)));
+ /* this count is used to distinguish original and retransmitted skb */
+ inet_csk(sk)->icsk_retransmits++;
+
+ return dccp_transmit_skb(sk, skb_clone(sk->sk_send_head, GFP_ATOMIC));
}
struct sk_buff *dccp_make_response(struct sock *sk, struct dst_entry *dst,
--- a/net/dccp/timer.c
+++ b/net/dccp/timer.c
@@ -99,21 +99,11 @@ static void dccp_retransmit_timer(struct sock *sk)
}
/*
- * sk->sk_send_head has to have one skb with
- * DCCP_SKB_CB(skb)->dccpd_type set to one of the retransmittable DCCP
- * packet types. The only packets eligible for retransmission are:
- * -- Requests in client-REQUEST state (sec. 8.1.1)
- * -- Acks in client-PARTOPEN state (sec. 8.1.5)
- * -- CloseReq in server-CLOSEREQ state (sec. 8.3)
- * -- Close in node-CLOSING state (sec. 8.3) */
- BUG_TRAP(sk->sk_send_head != NULL);
-
- /*
* More than than 4MSL (8 minutes) has passed, a RESET(aborted) was
* sent, no need to retransmit, this sock is dead.
*/
if (dccp_write_timeout(sk))
- goto out;
+ return;
/*
* We want to know the number of packets retransmitted, not the
@@ -122,30 +112,28 @@ static void dccp_retransmit_timer(struct sock *sk)
if (icsk->icsk_retransmits == 0)
DCCP_INC_STATS_BH(DCCP_MIB_TIMEOUTS);
- if (dccp_retransmit_skb(sk, sk->sk_send_head) < 0) {
+ if (dccp_retransmit_skb(sk) != 0) {
/*
* Retransmission failed because of local congestion,
* do not backoff.
*/
- if (icsk->icsk_retransmits == 0)
+ if (--icsk->icsk_retransmits == 0)
icsk->icsk_retransmits = 1;
inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
min(icsk->icsk_rto,
TCP_RESOURCE_PROBE_INTERVAL),
DCCP_RTO_MAX);
- goto out;
+ return;
}
backoff:
icsk->icsk_backoff++;
- icsk->icsk_retransmits++;
icsk->icsk_rto = min(icsk->icsk_rto << 1, DCCP_RTO_MAX);
inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, icsk->icsk_rto,
DCCP_RTO_MAX);
if (icsk->icsk_retransmits > sysctl_dccp_retries1)
__sk_dst_reset(sk);
-out:;
}
static void dccp_write_timer(unsigned long data)
--
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