linux/net/dccp/minisocks.c
Gerrit Renker bfbddd085a dccp: Fix the adjustments to AWL and SWL
This fixes a problem and a potential loophole with regard to seqno/ackno
validity: the problem is that the initial adjustments to AWL/SWL were
only performed at the begin of the connection, during the handshake.

Since the Sequence Window feature is always greater than Wmin=32 (7.5.2), 
it is however necessary to perform these adjustments at least for the first
W/W' (variables as per 7.5.1) packets in the lifetime of a connection.

This requirement is complicated by the fact that W/W' can change at any time
during the lifetime of a connection.

Therefore the consequence is to perform this safety check each time SWL/AWL
are updated.

A second problem solved by this patch is that the remote/local Sequence Window
feature values (which set the bounds for AWL/SWL/SWH) are undefined until the
feature negotiation has completed.

During the initial handshake we have more stringent sequence number protection,
the changes added by this patch effect that {A,S}W{L,H} are within the correct
bounds at the instant that feature negotiation completes (since the SeqWin
feature activation handlers call dccp_update_gsr/gss()). 

A detailed rationale is below -- can be removed from the commit message.


1. Server sequence number checks during initial handshake
---------------------------------------------------------
The server can not use the fields of the listening socket for seqno/ackno checks
and thus needs to store all relevant information on a per-connection basis on
the dccp_request socket. This is a size-constrained structure and has currently
only ISS (dreq_iss) and ISR (dreq_isr) defined.
Adding further fields (SW{L,H}, AW{L,H}) would increase the size of the struct
and it is questionable whether this will have any practical gain. The currently
implemented solution is as follows.
 * receiving first Request: dccp_v{4,6}_conn_request sets 
                            ISR := P.seqno, ISS := dccp_v{4,6}_init_sequence()

 * sending first Response:  dccp_v{4,6}_send_response via dccp_make_response()	
                            sets P.seqno := ISS, sets P.ackno := ISR

 * receiving retransmitted Request: dccp_check_req() overrides ISR := P.seqno

 * answering retransmitted Request: dccp_make_response() sets ISS += 1,
                                    otherwise as per first Response

 * completing the handshake: succeeds in dccp_check_req() for the first Ack
                             where P.ackno == ISS (P.seqno is not tested)

 * creating child socket: ISS, ISR are copied from the request_sock

This solution will succeed whenever the server can receive the Request and the
subsequent Ack in succession, without retransmissions. If there is packet loss,
the client needs to retransmit until this condition succeeds; it will otherwise
eventually give up. Adding further fields to the request_sock could increase
the robustness a bit, in that it would make possible to let a reordered Ack
(from a retransmitted Response) pass. The argument against such a solution is
that if the packet loss is not persistent and an Ack gets through, why not
wait for the one answering the original response: if the loss is persistent, it
is probably better to not start the connection in the first place.

Long story short: the present design (by Arnaldo) is simple and will likely work
just as well as a more complicated solution. As a consequence, {A,S}W{L,H} are
not needed until the moment the request_sock is cloned into the accept queue.

At that stage feature negotiation has completed, so that the values for the local
and remote Sequence Window feature (7.5.2) are known, i.e. we are now in a better
position to compute {A,S}W{L,H}.


2. Client sequence number checks during initial handshake
---------------------------------------------------------
Until entering PARTOPEN the client does not need the adjustments, since it 
constrains the Ack window to the packet it sent.

 * sending first Request: dccp_v{4,6}_connect() choose ISS, 
                          dccp_connect() then sets GAR := ISS (as per 8.5),
			  dccp_transmit_skb() (with the previous bug fix) sets
			         GSS := ISS, AWL := ISS, AWH := GSS
 * n-th retransmitted Request (with previous patch):
	                  dccp_retransmit_skb() via timer calls
			  dccp_transmit_skb(), which sets GSS := ISS+n
                          and then AWL := ISS, AWH := ISS+n
	                  
 * receiving any Response: dccp_rcv_request_sent_state_process() 
	                   -- accepts packet if AWL <= P.ackno <= AWH;
			   -- sets GSR = ISR = P.seqno

 * sending the Ack completing the handshake: dccp_send_ack() calls 
                           dccp_transmit_skb(), which sets GSS += 1
			   and AWL := ISS, AWH := GSS
			   

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
2008-09-04 07:45:35 +02:00

277 lines
7.8 KiB
C

/*
* net/dccp/minisocks.c
*
* An implementation of the DCCP protocol
* Arnaldo Carvalho de Melo <acme@conectiva.com.br>
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version
* 2 of the License, or (at your option) any later version.
*/
#include <linux/dccp.h>
#include <linux/kernel.h>
#include <linux/skbuff.h>
#include <linux/timer.h>
#include <net/sock.h>
#include <net/xfrm.h>
#include <net/inet_timewait_sock.h>
#include "ackvec.h"
#include "ccid.h"
#include "dccp.h"
#include "feat.h"
struct inet_timewait_death_row dccp_death_row = {
.sysctl_max_tw_buckets = NR_FILE * 2,
.period = DCCP_TIMEWAIT_LEN / INET_TWDR_TWKILL_SLOTS,
.death_lock = __SPIN_LOCK_UNLOCKED(dccp_death_row.death_lock),
.hashinfo = &dccp_hashinfo,
.tw_timer = TIMER_INITIALIZER(inet_twdr_hangman, 0,
(unsigned long)&dccp_death_row),
.twkill_work = __WORK_INITIALIZER(dccp_death_row.twkill_work,
inet_twdr_twkill_work),
/* Short-time timewait calendar */
.twcal_hand = -1,
.twcal_timer = TIMER_INITIALIZER(inet_twdr_twcal_tick, 0,
(unsigned long)&dccp_death_row),
};
EXPORT_SYMBOL_GPL(dccp_death_row);
void dccp_time_wait(struct sock *sk, int state, int timeo)
{
struct inet_timewait_sock *tw = NULL;
if (dccp_death_row.tw_count < dccp_death_row.sysctl_max_tw_buckets)
tw = inet_twsk_alloc(sk, state);
if (tw != NULL) {
const struct inet_connection_sock *icsk = inet_csk(sk);
const int rto = (icsk->icsk_rto << 2) - (icsk->icsk_rto >> 1);
#if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
if (tw->tw_family == PF_INET6) {
const struct ipv6_pinfo *np = inet6_sk(sk);
struct inet6_timewait_sock *tw6;
tw->tw_ipv6_offset = inet6_tw_offset(sk->sk_prot);
tw6 = inet6_twsk((struct sock *)tw);
ipv6_addr_copy(&tw6->tw_v6_daddr, &np->daddr);
ipv6_addr_copy(&tw6->tw_v6_rcv_saddr, &np->rcv_saddr);
tw->tw_ipv6only = np->ipv6only;
}
#endif
/* Linkage updates. */
__inet_twsk_hashdance(tw, sk, &dccp_hashinfo);
/* Get the TIME_WAIT timeout firing. */
if (timeo < rto)
timeo = rto;
tw->tw_timeout = DCCP_TIMEWAIT_LEN;
if (state == DCCP_TIME_WAIT)
timeo = DCCP_TIMEWAIT_LEN;
inet_twsk_schedule(tw, &dccp_death_row, timeo,
DCCP_TIMEWAIT_LEN);
inet_twsk_put(tw);
} else {
/* Sorry, if we're out of memory, just CLOSE this
* socket up. We've got bigger problems than
* non-graceful socket closings.
*/
DCCP_WARN("time wait bucket table overflow\n");
}
dccp_done(sk);
}
struct sock *dccp_create_openreq_child(struct sock *sk,
const struct request_sock *req,
const struct sk_buff *skb)
{
/*
* Step 3: Process LISTEN state
*
* (* Generate a new socket and switch to that socket *)
* Set S := new socket for this port pair
*/
struct sock *newsk = inet_csk_clone(sk, req, GFP_ATOMIC);
if (newsk != NULL) {
struct dccp_request_sock *dreq = dccp_rsk(req);
struct inet_connection_sock *newicsk = inet_csk(newsk);
struct dccp_sock *newdp = dccp_sk(newsk);
newdp->dccps_role = DCCP_ROLE_SERVER;
newdp->dccps_hc_rx_ackvec = NULL;
newdp->dccps_service_list = NULL;
newdp->dccps_service = dreq->dreq_service;
newdp->dccps_timestamp_echo = dreq->dreq_timestamp_echo;
newdp->dccps_timestamp_time = dreq->dreq_timestamp_time;
newicsk->icsk_rto = DCCP_TIMEOUT_INIT;
INIT_LIST_HEAD(&newdp->dccps_featneg);
/*
* Step 3: Process LISTEN state
*
* Choose S.ISS (initial seqno) or set from Init Cookies
* Initialize S.GAR := S.ISS
* Set S.ISR, S.GSR from packet (or Init Cookies)
*
* Setting AWL/AWH and SWL/SWH happens as part of the feature
* activation below, as these windows all depend on the local
* and remote Sequence Window feature values (7.5.2).
*/
newdp->dccps_gss = newdp->dccps_iss = dreq->dreq_iss;
newdp->dccps_gar = newdp->dccps_iss;
newdp->dccps_gsr = newdp->dccps_isr = dreq->dreq_isr;
/*
* Activate features: initialise CCIDs, sequence windows etc.
*/
if (dccp_feat_activate_values(newsk, &dreq->dreq_featneg)) {
/* It is still raw copy of parent, so invalidate
* destructor and make plain sk_free() */
newsk->sk_destruct = NULL;
sk_free(newsk);
return NULL;
}
dccp_init_xmit_timers(newsk);
DCCP_INC_STATS_BH(DCCP_MIB_PASSIVEOPENS);
}
return newsk;
}
EXPORT_SYMBOL_GPL(dccp_create_openreq_child);
/*
* Process an incoming packet for RESPOND sockets represented
* as an request_sock.
*/
struct sock *dccp_check_req(struct sock *sk, struct sk_buff *skb,
struct request_sock *req,
struct request_sock **prev)
{
struct sock *child = NULL;
struct dccp_request_sock *dreq = dccp_rsk(req);
/* Check for retransmitted REQUEST */
if (dccp_hdr(skb)->dccph_type == DCCP_PKT_REQUEST) {
if (after48(DCCP_SKB_CB(skb)->dccpd_seq, dreq->dreq_isr)) {
dccp_pr_debug("Retransmitted REQUEST\n");
dreq->dreq_isr = DCCP_SKB_CB(skb)->dccpd_seq;
/*
* Send another RESPONSE packet
* To protect against Request floods, increment retrans
* counter (backoff, monitored by dccp_response_timer).
*/
req->retrans++;
req->rsk_ops->rtx_syn_ack(sk, req);
}
/* Network Duplicate, discard packet */
return NULL;
}
DCCP_SKB_CB(skb)->dccpd_reset_code = DCCP_RESET_CODE_PACKET_ERROR;
if (dccp_hdr(skb)->dccph_type != DCCP_PKT_ACK &&
dccp_hdr(skb)->dccph_type != DCCP_PKT_DATAACK)
goto drop;
/* Invalid ACK */
if (DCCP_SKB_CB(skb)->dccpd_ack_seq != dreq->dreq_iss) {
dccp_pr_debug("Invalid ACK number: ack_seq=%llu, "
"dreq_iss=%llu\n",
(unsigned long long)
DCCP_SKB_CB(skb)->dccpd_ack_seq,
(unsigned long long) dreq->dreq_iss);
goto drop;
}
if (dccp_parse_options(sk, dreq, skb))
goto drop;
child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL);
if (child == NULL)
goto listen_overflow;
inet_csk_reqsk_queue_unlink(sk, req, prev);
inet_csk_reqsk_queue_removed(sk, req);
inet_csk_reqsk_queue_add(sk, req, child);
out:
return child;
listen_overflow:
dccp_pr_debug("listen_overflow!\n");
DCCP_SKB_CB(skb)->dccpd_reset_code = DCCP_RESET_CODE_TOO_BUSY;
drop:
if (dccp_hdr(skb)->dccph_type != DCCP_PKT_RESET)
req->rsk_ops->send_reset(sk, skb);
inet_csk_reqsk_queue_drop(sk, req, prev);
goto out;
}
EXPORT_SYMBOL_GPL(dccp_check_req);
/*
* Queue segment on the new socket if the new socket is active,
* otherwise we just shortcircuit this and continue with
* the new socket.
*/
int dccp_child_process(struct sock *parent, struct sock *child,
struct sk_buff *skb)
{
int ret = 0;
const int state = child->sk_state;
if (!sock_owned_by_user(child)) {
ret = dccp_rcv_state_process(child, skb, dccp_hdr(skb),
skb->len);
/* Wakeup parent, send SIGIO */
if (state == DCCP_RESPOND && child->sk_state != state)
parent->sk_data_ready(parent, 0);
} else {
/* Alas, it is possible again, because we do lookup
* in main socket hash table and lock on listening
* socket does not protect us more.
*/
sk_add_backlog(child, skb);
}
bh_unlock_sock(child);
sock_put(child);
return ret;
}
EXPORT_SYMBOL_GPL(dccp_child_process);
void dccp_reqsk_send_ack(struct sock *sk, struct sk_buff *skb,
struct request_sock *rsk)
{
DCCP_BUG("DCCP-ACK packets are never sent in LISTEN/RESPOND state");
}
EXPORT_SYMBOL_GPL(dccp_reqsk_send_ack);
int dccp_reqsk_init(struct request_sock *req,
struct dccp_sock const *dp, struct sk_buff const *skb)
{
struct dccp_request_sock *dreq = dccp_rsk(req);
inet_rsk(req)->rmt_port = dccp_hdr(skb)->dccph_sport;
inet_rsk(req)->acked = 0;
dreq->dreq_timestamp_echo = 0;
/* inherit feature negotiation options from listening socket */
return dccp_feat_clone_list(&dp->dccps_featneg, &dreq->dreq_featneg);
}
EXPORT_SYMBOL_GPL(dccp_reqsk_init);