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netfilter: handle the connecting collision properly in nf_conntrack_proto_sctp

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In Scenario A and B below, as the delayed INIT_ACK always changes the peer
vtag, SCTP ct with the incorrect vtag may cause packet loss.

Scenario A: INIT_ACK is delayed until the peer receives its own INIT_ACK

  192.168.1.2 > 192.168.1.1: [INIT] [init tag: 1328086772]
    192.168.1.1 > 192.168.1.2: [INIT] [init tag: 1414468151]
    192.168.1.2 > 192.168.1.1: [INIT ACK] [init tag: 1328086772]
  192.168.1.1 > 192.168.1.2: [INIT ACK] [init tag: 1650211246] *
  192.168.1.2 > 192.168.1.1: [COOKIE ECHO]
    192.168.1.1 > 192.168.1.2: [COOKIE ECHO]
    192.168.1.2 > 192.168.1.1: [COOKIE ACK]

Scenario B: INIT_ACK is delayed until the peer completes its own handshake

  192.168.1.2 > 192.168.1.1: sctp (1) [INIT] [init tag: 3922216408]
    192.168.1.1 > 192.168.1.2: sctp (1) [INIT] [init tag: 144230885]
    192.168.1.2 > 192.168.1.1: sctp (1) [INIT ACK] [init tag: 3922216408]
    192.168.1.1 > 192.168.1.2: sctp (1) [COOKIE ECHO]
    192.168.1.2 > 192.168.1.1: sctp (1) [COOKIE ACK]
  192.168.1.1 > 192.168.1.2: sctp (1) [INIT ACK] [init tag: 3914796021] *

This patch fixes it as below:

In SCTP_CID_INIT processing:
- clear ct->proto.sctp.init[!dir] if ct->proto.sctp.init[dir] &&
  ct->proto.sctp.init[!dir]. (Scenario E)
- set ct->proto.sctp.init[dir].

In SCTP_CID_INIT_ACK processing:
- drop it if !ct->proto.sctp.init[!dir] && ct->proto.sctp.vtag[!dir] &&
  ct->proto.sctp.vtag[!dir] != ih->init_tag. (Scenario B, Scenario C)
- drop it if ct->proto.sctp.init[dir] && ct->proto.sctp.init[!dir] &&
  ct->proto.sctp.vtag[!dir] != ih->init_tag. (Scenario A)

In SCTP_CID_COOKIE_ACK processing:
- clear ct->proto.sctp.init[dir] and ct->proto.sctp.init[!dir].
  (Scenario D)

Also, it's important to allow the ct state to move forward with cookie_echo
and cookie_ack from the opposite dir for the collision scenarios.

There are also other Scenarios where it should allow the packet through,
addressed by the processing above:

Scenario C: new CT is created by INIT_ACK.

Scenario D: start INIT on the existing ESTABLISHED ct.

Scenario E: start INIT after the old collision on the existing ESTABLISHED
ct.

  192.168.1.2 > 192.168.1.1: sctp (1) [INIT] [init tag: 3922216408]
  192.168.1.1 > 192.168.1.2: sctp (1) [INIT] [init tag: 144230885]
  (both side are stopped, then start new connection again in hours)
  192.168.1.2 > 192.168.1.1: sctp (1) [INIT] [init tag: 242308742]

Fixes: 9fb9cbb108 ("[NETFILTER]: Add nf_conntrack subsystem.")
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
This commit is contained in:
Xin Long 2023-10-03 13:17:53 -04:00 committed by Florian Westphal
parent af84f9e447
commit 8e56b063c8
2 changed files with 34 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
include/linux/netfilter/nf_conntrack_sctp.h
View File

@ -9,6 +9,7 @@ struct ip_ct_sctp {
enum sctp_conntrack state;
__be32 vtag[IP_CT_DIR_MAX];
u8 init[IP_CT_DIR_MAX];
u8 last_dir;
u8 flags;
};

43
net/netfilter/nf_conntrack_proto_sctp.c
View File

@ -112,7 +112,7 @@ static const u8 sctp_conntracks[2][11][SCTP_CONNTRACK_MAX] = {
/* shutdown_ack */ {sSA, sCL, sCW, sCE, sES, sSA, sSA, sSA, sSA},
/* error */ {sCL, sCL, sCW, sCE, sES, sSS, sSR, sSA, sCL},/* Can't have Stale cookie*/
/* cookie_echo */ {sCL, sCL, sCE, sCE, sES, sSS, sSR, sSA, sCL},/* 5.2.4 - Big TODO */
/* cookie_ack */ {sCL, sCL, sCW, sCE, sES, sSS, sSR, sSA, sCL},/* Can't come in orig dir */
/* cookie_ack */ {sCL, sCL, sCW, sES, sES, sSS, sSR, sSA, sCL},/* Can't come in orig dir */
/* shutdown_comp*/ {sCL, sCL, sCW, sCE, sES, sSS, sSR, sCL, sCL},
/* heartbeat */ {sHS, sCL, sCW, sCE, sES, sSS, sSR, sSA, sHS},
/* heartbeat_ack*/ {sCL, sCL, sCW, sCE, sES, sSS, sSR, sSA, sHS},
@ -126,7 +126,7 @@ static const u8 sctp_conntracks[2][11][SCTP_CONNTRACK_MAX] = {
/* shutdown */ {sIV, sCL, sCW, sCE, sSR, sSS, sSR, sSA, sIV},
/* shutdown_ack */ {sIV, sCL, sCW, sCE, sES, sSA, sSA, sSA, sIV},
/* error */ {sIV, sCL, sCW, sCL, sES, sSS, sSR, sSA, sIV},
/* cookie_echo */ {sIV, sCL, sCW, sCE, sES, sSS, sSR, sSA, sIV},/* Can't come in reply dir */
/* cookie_echo */ {sIV, sCL, sCE, sCE, sES, sSS, sSR, sSA, sIV},/* Can't come in reply dir */
/* cookie_ack */ {sIV, sCL, sCW, sES, sES, sSS, sSR, sSA, sIV},
/* shutdown_comp*/ {sIV, sCL, sCW, sCE, sES, sSS, sSR, sCL, sIV},
/* heartbeat */ {sIV, sCL, sCW, sCE, sES, sSS, sSR, sSA, sHS},
@ -412,6 +412,9 @@ int nf_conntrack_sctp_packet(struct nf_conn *ct,
/* (D) vtag must be same as init_vtag as found in INIT_ACK */
if (sh->vtag != ct->proto.sctp.vtag[dir])
goto out_unlock;
} else if (sch->type == SCTP_CID_COOKIE_ACK) {
ct->proto.sctp.init[dir] = 0;
ct->proto.sctp.init[!dir] = 0;
} else if (sch->type == SCTP_CID_HEARTBEAT) {
if (ct->proto.sctp.vtag[dir] == 0) {
pr_debug("Setting %d vtag %x for dir %d\n", sch->type, sh->vtag, dir);
@ -461,16 +464,18 @@ int nf_conntrack_sctp_packet(struct nf_conn *ct,
}
/* If it is an INIT or an INIT ACK note down the vtag */
if (sch->type == SCTP_CID_INIT ||
sch->type == SCTP_CID_INIT_ACK) {
struct sctp_inithdr _inithdr, *ih;
if (sch->type == SCTP_CID_INIT) {
struct sctp_inithdr _ih, *ih;
ih = skb_header_pointer(skb, offset + sizeof(_sch),
sizeof(_inithdr), &_inithdr);
if (ih == NULL)
ih = skb_header_pointer(skb, offset + sizeof(_sch), sizeof(*ih), &_ih);
if (!ih)
goto out_unlock;
pr_debug("Setting vtag %x for dir %d\n",
ih->init_tag, !dir);
if (ct->proto.sctp.init[dir] && ct->proto.sctp.init[!dir])
ct->proto.sctp.init[!dir] = 0;
ct->proto.sctp.init[dir] = 1;
pr_debug("Setting vtag %x for dir %d\n", ih->init_tag, !dir);
ct->proto.sctp.vtag[!dir] = ih->init_tag;
/* don't renew timeout on init retransmit so
@ -481,6 +486,24 @@ int nf_conntrack_sctp_packet(struct nf_conn *ct,
old_state == SCTP_CONNTRACK_CLOSED &&
nf_ct_is_confirmed(ct))
ignore = true;
} else if (sch->type == SCTP_CID_INIT_ACK) {
struct sctp_inithdr _ih, *ih;
__be32 vtag;
ih = skb_header_pointer(skb, offset + sizeof(_sch), sizeof(*ih), &_ih);
if (!ih)
goto out_unlock;
vtag = ct->proto.sctp.vtag[!dir];
if (!ct->proto.sctp.init[!dir] && vtag && vtag != ih->init_tag)
goto out_unlock;
/* collision */
if (ct->proto.sctp.init[dir] && ct->proto.sctp.init[!dir] &&
vtag != ih->init_tag)
goto out_unlock;
pr_debug("Setting vtag %x for dir %d\n", ih->init_tag, !dir);
ct->proto.sctp.vtag[!dir] = ih->init_tag;
}
ct->proto.sctp.state = new_state;