[PATCH net-next 0/5] sctp: update from rfc7829

[PATCH net-next 0/5] sctp: update from rfc7829

[Xin Long]

SCTP-PF was implemented based on a Internet-Draft in 2012:

  https://tools.ietf.org/html/draft-nishida-tsvwg-sctp-failover-05

It's been updated quite a few by rfc7829 in 2016.

This patchset adds the following features:

  1. add SCTP_ADDR_POTENTIALLY_FAILED notification
  2. add pf_expose per netns/sock/asoc
  3. add SCTP_EXPOSE_POTENTIALLY_FAILED_STATE sockopt
  4. add ps_retrans per netns/sock/asoc/transport
     (Primary Path Switchover)
  5. add spt_pathcpthld for SCTP_PEER_ADDR_THLDS sockopt

Xin Long (5):
  sctp: add SCTP_ADDR_POTENTIALLY_FAILED notification
  sctp: add pf_expose per netns and sock and asoc
  sctp: add SCTP_EXPOSE_POTENTIALLY_FAILED_STATE sockopt
  sctp: add support for Primary Path Switchover
  sctp: add spt_pathcpthld in struct sctp_paddrthlds

 include/net/netns/sctp.h   | 13 ++++++
 include/net/sctp/structs.h | 13 ++++--
 include/uapi/linux/sctp.h  |  4 ++
 net/sctp/associola.c       | 28 ++++++-------
 net/sctp/protocol.c        |  6 +++
 net/sctp/sm_sideeffect.c   |  5 +++
 net/sctp/socket.c          | 99 +++++++++++++++++++++++++++++++++++++++++++++-
 net/sctp/sysctl.c          | 16 ++++++++
 8 files changed, 165 insertions(+), 19 deletions(-)

-- 
2.1.0

[PATCH net-next 1/5] sctp: add SCTP_ADDR_POTENTIALLY_FAILED notification

[Xin Long]

SCTP Quick failover draft section 5.1, point 5 has been removed
from rfc7829. Instead, "the sender SHOULD (i) notify the Upper
Layer Protocol (ULP) about this state transition", as said in
section 3.2, point 8.

So this patch is to add SCTP_ADDR_POTENTIALLY_FAILED, defined
in section 7.1, "which is reported if the affected address
becomes PF". Also remove transport cwnd's update when moving
from PF back to ACTIVE , which is no longer in rfc7829 either.

Signed-off-by: Xin Long <lucien.xin@gmail.com>
---
 include/uapi/linux/sctp.h |  1 +
 net/sctp/associola.c      | 17 ++++-------------
 2 files changed, 5 insertions(+), 13 deletions(-)

diff --git a/include/uapi/linux/sctp.h b/include/uapi/linux/sctp.h
index 6d5b164..45a85d7 100644
--- a/include/uapi/linux/sctp.h
+++ b/include/uapi/linux/sctp.h
@@ -410,6 +410,7 @@ enum sctp_spc_state {
 	SCTP_ADDR_ADDED,
 	SCTP_ADDR_MADE_PRIM,
 	SCTP_ADDR_CONFIRMED,
+	SCTP_ADDR_POTENTIALLY_FAILED,
 };
 
 
diff --git a/net/sctp/associola.c b/net/sctp/associola.c
index d2ffc9a..7278b7e 100644
--- a/net/sctp/associola.c
+++ b/net/sctp/associola.c
@@ -798,14 +798,6 @@ void sctp_assoc_control_transport(struct sctp_association *asoc,
 			spc_state = SCTP_ADDR_CONFIRMED;
 		else
 			spc_state = SCTP_ADDR_AVAILABLE;
-		/* Don't inform ULP about transition from PF to
-		 * active state and set cwnd to 1 MTU, see SCTP
-		 * Quick failover draft section 5.1, point 5
-		 */
-		if (transport->state == SCTP_PF) {
-			ulp_notify = false;
-			transport->cwnd = asoc->pathmtu;
-		}
 		transport->state = SCTP_ACTIVE;
 		break;
 
@@ -814,19 +806,18 @@ void sctp_assoc_control_transport(struct sctp_association *asoc,
 		 * to inactive state.  Also, release the cached route since
 		 * there may be a better route next time.
 		 */
-		if (transport->state != SCTP_UNCONFIRMED)
+		if (transport->state != SCTP_UNCONFIRMED) {
 			transport->state = SCTP_INACTIVE;
-		else {
+			spc_state = SCTP_ADDR_UNREACHABLE;
+		} else {
 			sctp_transport_dst_release(transport);
 			ulp_notify = false;
 		}
-
-		spc_state = SCTP_ADDR_UNREACHABLE;
 		break;
 
 	case SCTP_TRANSPORT_PF:
 		transport->state = SCTP_PF;
-		ulp_notify = false;
+		spc_state = SCTP_ADDR_POTENTIALLY_FAILED;
 		break;
 
 	default:
-- 
2.1.0

[PATCH net-next 2/5] sctp: add pf_expose per netns and sock and asoc

[Xin Long]

As said in rfc7829, section 3, point 12:

  The SCTP stack SHOULD expose the PF state of its destination
  addresses to the ULP as well as provide the means to notify the
  ULP of state transitions of its destination addresses from
  active to PF, and vice versa.  However, it is recommended that
  an SCTP stack implementing SCTP-PF also allows for the ULP to be
  kept ignorant of the PF state of its destinations and the
  associated state transitions, thus allowing for retention of the
  simpler state transition model of [RFC4960] in the ULP.

Not only does it allow to expose the PF state to ULP, but also
allow to ignore sctp-pf to ULP.

So this patch is to add pf_expose per netns, sock and asoc. And in
sctp_assoc_control_transport(), ulp_notify will be set to false if
asoc->expose is not set.

It also allows a user to change pf_expose per netns by sysctl, and
pf_expose per sock and asoc will be initialized with it.

Note that pf_expose also works for SCTP_GET_PEER_ADDR_INFO sockopt,
to not allow a user to query the state of a sctp-pf peer address
when pf_expose is not enabled, as said in section 7.3.

Signed-off-by: Xin Long <lucien.xin@gmail.com>
---
 include/net/netns/sctp.h   |  7 +++++++
 include/net/sctp/structs.h |  2 ++
 include/uapi/linux/sctp.h  |  1 +
 net/sctp/associola.c       | 10 ++++++++--
 net/sctp/protocol.c        |  3 +++
 net/sctp/socket.c          | 12 ++++++++++--
 net/sctp/sysctl.c          |  7 +++++++
 7 files changed, 38 insertions(+), 4 deletions(-)

diff --git a/include/net/netns/sctp.h b/include/net/netns/sctp.h
index bdc0f27..5234940c 100644
--- a/include/net/netns/sctp.h
+++ b/include/net/netns/sctp.h
@@ -97,6 +97,13 @@ struct netns_sctp {
 	int pf_enable;
 
 	/*
+	 * Disable Potentially-Failed state exposure, enabled by default
+	 * pf_expose	-  0  : disable pf state exposure
+	 *		- >0  : enable  pf state exposure
+	 */
+	int pf_expose;
+
+	/*
 	 * Policy for preforming sctp/socket accounting
 	 * 0   - do socket level accounting, all assocs share sk_sndbuf
 	 * 1   - do sctp accounting, each asoc may use sk_sndbuf bytes
diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs.h
index 503fbc3..c2d3317 100644
--- a/include/net/sctp/structs.h
+++ b/include/net/sctp/structs.h
@@ -215,6 +215,7 @@ struct sctp_sock {
 	__u32 adaptation_ind;
 	__u32 pd_point;
 	__u16	nodelay:1,
+		pf_expose:1,
 		reuse:1,
 		disable_fragments:1,
 		v4mapped:1,
@@ -2053,6 +2054,7 @@ struct sctp_association {
 
 	__u8 need_ecne:1,	/* Need to send an ECNE Chunk? */
 	     temp:1,		/* Is it a temporary association? */
+	     pf_expose:1,       /* Expose pf state? */
 	     force_delay:1;
 
 	__u8 strreset_enable;
diff --git a/include/uapi/linux/sctp.h b/include/uapi/linux/sctp.h
index 45a85d7..b6649d6 100644
--- a/include/uapi/linux/sctp.h
+++ b/include/uapi/linux/sctp.h
@@ -920,6 +920,7 @@ struct sctp_paddrinfo {
 enum sctp_spinfo_state {
 	SCTP_INACTIVE,
 	SCTP_PF,
+#define	SCTP_POTENTIALLY_FAILED		SCTP_PF
 	SCTP_ACTIVE,
 	SCTP_UNCONFIRMED,
 	SCTP_UNKNOWN = 0xffff  /* Value used for transport state unknown */
diff --git a/net/sctp/associola.c b/net/sctp/associola.c
index 7278b7e..461b1ffa 100644
--- a/net/sctp/associola.c
+++ b/net/sctp/associola.c
@@ -86,6 +86,7 @@ static struct sctp_association *sctp_association_init(
 	 */
 	asoc->max_retrans = sp->assocparams.sasoc_asocmaxrxt;
 	asoc->pf_retrans  = sp->pf_retrans;
+	asoc->pf_expose   = sp->pf_expose;
 
 	asoc->rto_initial = msecs_to_jiffies(sp->rtoinfo.srto_initial);
 	asoc->rto_max = msecs_to_jiffies(sp->rtoinfo.srto_max);
@@ -793,7 +794,9 @@ void sctp_assoc_control_transport(struct sctp_association *asoc,
 		 * to heartbeat success, report the SCTP_ADDR_CONFIRMED
 		 * state to the user, otherwise report SCTP_ADDR_AVAILABLE.
 		 */
-		if (SCTP_UNCONFIRMED == transport->state &&
+		if (transport->state == SCTP_PF && !asoc->pf_expose)
+			ulp_notify = false;
+		if (transport->state && SCTP_UNCONFIRMED &&
 		    SCTP_HEARTBEAT_SUCCESS == error)
 			spc_state = SCTP_ADDR_CONFIRMED;
 		else
@@ -817,7 +820,10 @@ void sctp_assoc_control_transport(struct sctp_association *asoc,
 
 	case SCTP_TRANSPORT_PF:
 		transport->state = SCTP_PF;
-		spc_state = SCTP_ADDR_POTENTIALLY_FAILED;
+		if (!asoc->pf_expose)
+			ulp_notify = false;
+		else
+			spc_state = SCTP_ADDR_POTENTIALLY_FAILED;
 		break;
 
 	default:
diff --git a/net/sctp/protocol.c b/net/sctp/protocol.c
index b48ffe8..de0f15f 100644
--- a/net/sctp/protocol.c
+++ b/net/sctp/protocol.c
@@ -1220,6 +1220,9 @@ static int __net_init sctp_defaults_init(struct net *net)
 	/* Enable pf state by default */
 	net->sctp.pf_enable = 1;
 
+	/* Enable pf state exposure by default */
+	net->sctp.pf_expose = 1;
+
 	/* Association.Max.Retrans  - 10 attempts
 	 * Path.Max.Retrans         - 5  attempts (per destination address)
 	 * Max.Init.Retransmits     - 8  attempts
diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index 3e50a97..33b93bb 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -5040,6 +5040,7 @@ static int sctp_init_sock(struct sock *sk)
 	sp->hbinterval  = net->sctp.hb_interval;
 	sp->pathmaxrxt  = net->sctp.max_retrans_path;
 	sp->pf_retrans  = net->sctp.pf_retrans;
+	sp->pf_expose   = net->sctp.pf_expose;
 	sp->pathmtu     = 0; /* allow default discovery */
 	sp->sackdelay   = net->sctp.sack_timeout;
 	sp->sackfreq	= 2;
@@ -5520,8 +5521,15 @@ static int sctp_getsockopt_peer_addr_info(struct sock *sk, int len,
 
 	transport = sctp_addr_id2transport(sk, &pinfo.spinfo_address,
 					   pinfo.spinfo_assoc_id);
-	if (!transport)
-		return -EINVAL;
+	if (!transport) {
+		retval = -EINVAL;
+		goto out;
+	}
+
+	if (transport->state == SCTP_PF && !transport->asoc->pf_expose) {
+		retval = -EACCES;
+		goto out;
+	}
 
 	pinfo.spinfo_assoc_id = sctp_assoc2id(transport->asoc);
 	pinfo.spinfo_state = transport->state;
diff --git a/net/sctp/sysctl.c b/net/sctp/sysctl.c
index 238cf17..eacc9a1 100644
--- a/net/sctp/sysctl.c
+++ b/net/sctp/sysctl.c
@@ -318,6 +318,13 @@ static struct ctl_table sctp_net_table[] = {
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec,
 	},
+	{
+		.procname	= "pf_expose",
+		.data		= &init_net.sctp.pf_expose,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec,
+	},
 
 	{ /* sentinel */ }
 };
-- 
2.1.0

[PATCH net-next 3/5] sctp: add SCTP_EXPOSE_POTENTIALLY_FAILED_STATE sockopt

[Xin Long]

This is a sockopt defined in section 7.3 of rfc7829: "Exposing
the Potentially Failed Path State", by which users can change
pf_expose per sock and asoc.

Signed-off-by: Xin Long <lucien.xin@gmail.com>
---
 include/uapi/linux/sctp.h |  1 +
 net/sctp/socket.c         | 76 +++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 77 insertions(+)

diff --git a/include/uapi/linux/sctp.h b/include/uapi/linux/sctp.h
index b6649d6..a15cc28 100644
--- a/include/uapi/linux/sctp.h
+++ b/include/uapi/linux/sctp.h
@@ -137,6 +137,7 @@ typedef __s32 sctp_assoc_t;
 #define SCTP_ASCONF_SUPPORTED	128
 #define SCTP_AUTH_SUPPORTED	129
 #define SCTP_ECN_SUPPORTED	130
+#define SCTP_EXPOSE_POTENTIALLY_FAILED_STATE	131
 
 /* PR-SCTP policies */
 #define SCTP_PR_SCTP_NONE	0x0000
diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index 33b93bb..e3a8e25 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -4588,6 +4588,37 @@ static int sctp_setsockopt_ecn_supported(struct sock *sk,
 	return retval;
 }
 
+static int sctp_setsockopt_pf_expose(struct sock *sk,
+				     char __user *optval,
+				     unsigned int optlen)
+{
+	struct sctp_assoc_value params;
+	struct sctp_association *asoc;
+	int retval = -EINVAL;
+
+	if (optlen != sizeof(params))
+		goto out;
+
+	if (copy_from_user(&params, optval, optlen)) {
+		retval = -EFAULT;
+		goto out;
+	}
+
+	asoc = sctp_id2assoc(sk, params.assoc_id);
+	if (!asoc && params.assoc_id != SCTP_FUTURE_ASSOC &&
+	    sctp_style(sk, UDP))
+		goto out;
+
+	if (asoc)
+		asoc->pf_expose = !!params.assoc_value;
+	else
+		sctp_sk(sk)->pf_expose = !!params.assoc_value;
+	retval = 0;
+
+out:
+	return retval;
+}
+
 /* API 6.2 setsockopt(), getsockopt()
  *
  * Applications use setsockopt() and getsockopt() to set or retrieve
@@ -4797,6 +4828,9 @@ static int sctp_setsockopt(struct sock *sk, int level, int optname,
 	case SCTP_ECN_SUPPORTED:
 		retval = sctp_setsockopt_ecn_supported(sk, optval, optlen);
 		break;
+	case SCTP_EXPOSE_POTENTIALLY_FAILED_STATE:
+		retval = sctp_setsockopt_pf_expose(sk, optval, optlen);
+		break;
 	default:
 		retval = -ENOPROTOOPT;
 		break;
@@ -7906,6 +7940,45 @@ static int sctp_getsockopt_ecn_supported(struct sock *sk, int len,
 	return retval;
 }
 
+static int sctp_getsockopt_pf_expose(struct sock *sk, int len,
+				     char __user *optval,
+				     int __user *optlen)
+{
+	struct sctp_assoc_value params;
+	struct sctp_association *asoc;
+	int retval = -EFAULT;
+
+	if (len < sizeof(params)) {
+		retval = -EINVAL;
+		goto out;
+	}
+
+	len = sizeof(params);
+	if (copy_from_user(&params, optval, len))
+		goto out;
+
+	asoc = sctp_id2assoc(sk, params.assoc_id);
+	if (!asoc && params.assoc_id != SCTP_FUTURE_ASSOC &&
+	    sctp_style(sk, UDP)) {
+		retval = -EINVAL;
+		goto out;
+	}
+
+	params.assoc_value = asoc ? asoc->pf_expose
+				  : sctp_sk(sk)->pf_expose;
+
+	if (put_user(len, optlen))
+		goto out;
+
+	if (copy_to_user(optval, &params, len))
+		goto out;
+
+	retval = 0;
+
+out:
+	return retval;
+}
+
 static int sctp_getsockopt(struct sock *sk, int level, int optname,
 			   char __user *optval, int __user *optlen)
 {
@@ -8118,6 +8191,9 @@ static int sctp_getsockopt(struct sock *sk, int level, int optname,
 	case SCTP_ECN_SUPPORTED:
 		retval = sctp_getsockopt_ecn_supported(sk, len, optval, optlen);
 		break;
+	case SCTP_EXPOSE_POTENTIALLY_FAILED_STATE:
+		retval = sctp_getsockopt_pf_expose(sk, len, optval, optlen);
+		break;
 	default:
 		retval = -ENOPROTOOPT;
 		break;
-- 
2.1.0

[PATCH net-next 4/5] sctp: add support for Primary Path Switchover

[Xin Long]

This is a new feature defined in section 5 of rfc7829: "Primary Path
Switchover". By introducing a new tunable parameter:

  Primary.Switchover.Max.Retrans (PSMR)

The primary path will be changed to another active path when the path
error counter on the old primary path exceeds PSMR, so that "the SCTP
sender is allowed to continue data transmission on a new working path
even when the old primary destination address becomes active again".

This patch is to add this tunable parameter, 'ps_retrans' per netns,
sock, asoc and transport. It also allows a user to change ps_retrans
per netns by sysctl, and ps_retrans per sock/asoc/transport will be
initialized with it.

The check will be done in sctp_do_8_2_transport_strike() when this
feature is enabled.

Note this feature is disabled by initializing 'ps_retrans' per netns
as 0xffff by default, and its value can't be less than 'pf_retrans'
when changing by sysctl.

Signed-off-by: Xin Long <lucien.xin@gmail.com>
---
 include/net/netns/sctp.h   |  6 ++++++
 include/net/sctp/structs.h | 11 ++++++++---
 net/sctp/associola.c       |  3 +++
 net/sctp/protocol.c        |  3 +++
 net/sctp/sm_sideeffect.c   |  5 +++++
 net/sctp/socket.c          |  1 +
 net/sctp/sysctl.c          |  9 +++++++++
 7 files changed, 35 insertions(+), 3 deletions(-)

diff --git a/include/net/netns/sctp.h b/include/net/netns/sctp.h
index 5234940c..cab0903 100644
--- a/include/net/netns/sctp.h
+++ b/include/net/netns/sctp.h
@@ -89,6 +89,12 @@ struct netns_sctp {
 	 */
 	int pf_retrans;
 
+	/* Primary.Switchover.Max.Retrans sysctl value
+	 * taken from:
+	 * https://tools.ietf.org/html/rfc7829
+	 */
+	int ps_retrans;
+
 	/*
 	 * Disable Potentially-Failed feature, the feature is enabled by default
 	 * pf_enable	-  0  : disable pf
diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs.h
index c2d3317..3680a93 100644
--- a/include/net/sctp/structs.h
+++ b/include/net/sctp/structs.h
@@ -184,7 +184,8 @@ struct sctp_sock {
 	__u32 flowlabel;
 	__u8  dscp;
 
-	int pf_retrans;
+	__u16 pf_retrans;
+	__u16 ps_retrans;
 
 	/* The initial Path MTU to use for new associations. */
 	__u32 pathmtu;
@@ -897,7 +898,9 @@ struct sctp_transport {
 	 * and will be initialized from the assocs value.  This can be changed
 	 * using the SCTP_PEER_ADDR_THLDS socket option
 	 */
-	int pf_retrans;
+	__u16 pf_retrans;
+	/* Used for primary path switchover. */
+	__u16 ps_retrans;
 	/* PMTU	      : The current known path MTU.  */
 	__u32 pathmtu;
 
@@ -1773,7 +1776,9 @@ struct sctp_association {
 	 * and will be initialized from the assocs value.  This can be
 	 * changed using the SCTP_PEER_ADDR_THLDS socket option
 	 */
-	int pf_retrans;
+	__u16 pf_retrans;
+	/* Used for primary path switchover. */
+	__u16 ps_retrans;
 
 	/* Maximum number of times the endpoint will retransmit INIT  */
 	__u16 max_init_attempts;
diff --git a/net/sctp/associola.c b/net/sctp/associola.c
index 461b1ffa..f63c56d 100644
--- a/net/sctp/associola.c
+++ b/net/sctp/associola.c
@@ -86,6 +86,7 @@ static struct sctp_association *sctp_association_init(
 	 */
 	asoc->max_retrans = sp->assocparams.sasoc_asocmaxrxt;
 	asoc->pf_retrans  = sp->pf_retrans;
+	asoc->ps_retrans  = sp->ps_retrans;
 	asoc->pf_expose   = sp->pf_expose;
 
 	asoc->rto_initial = msecs_to_jiffies(sp->rtoinfo.srto_initial);
@@ -625,6 +626,8 @@ struct sctp_transport *sctp_assoc_add_peer(struct sctp_association *asoc,
 
 	/* And the partial failure retrans threshold */
 	peer->pf_retrans = asoc->pf_retrans;
+	/* And the primary path switchover retrans threshold */
+	peer->ps_retrans = asoc->ps_retrans;
 
 	/* Initialize the peer's SACK delay timeout based on the
 	 * association configured value.
diff --git a/net/sctp/protocol.c b/net/sctp/protocol.c
index de0f15f..23f7631 100644
--- a/net/sctp/protocol.c
+++ b/net/sctp/protocol.c
@@ -1217,6 +1217,9 @@ static int __net_init sctp_defaults_init(struct net *net)
 	/* Max.Burst		    - 4 */
 	net->sctp.max_burst			= SCTP_DEFAULT_MAX_BURST;
 
+	/* Disable of Primary Path Switchover by default */
+	net->sctp.ps_retrans = 0xffff;
+
 	/* Enable pf state by default */
 	net->sctp.pf_enable = 1;
 
diff --git a/net/sctp/sm_sideeffect.c b/net/sctp/sm_sideeffect.c
index 1cf5bb5..3948697 100644
--- a/net/sctp/sm_sideeffect.c
+++ b/net/sctp/sm_sideeffect.c
@@ -567,6 +567,11 @@ static void sctp_do_8_2_transport_strike(struct sctp_cmd_seq *commands,
 					     SCTP_FAILED_THRESHOLD);
 	}
 
+	if (transport->error_count > transport->ps_retrans &&
+	    asoc->peer.primary_path == transport &&
+	    asoc->peer.active_path != transport)
+		sctp_assoc_set_primary(asoc, asoc->peer.active_path);
+
 	/* E2) For the destination address for which the timer
 	 * expires, set RTO <- RTO * 2 ("back off the timer").  The
 	 * maximum value discussed in rule C7 above (RTO.max) may be
diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index e3a8e25..5e2098b 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -5074,6 +5074,7 @@ static int sctp_init_sock(struct sock *sk)
 	sp->hbinterval  = net->sctp.hb_interval;
 	sp->pathmaxrxt  = net->sctp.max_retrans_path;
 	sp->pf_retrans  = net->sctp.pf_retrans;
+	sp->ps_retrans  = net->sctp.ps_retrans;
 	sp->pf_expose   = net->sctp.pf_expose;
 	sp->pathmtu     = 0; /* allow default discovery */
 	sp->sackdelay   = net->sctp.sack_timeout;
diff --git a/net/sctp/sysctl.c b/net/sctp/sysctl.c
index eacc9a1..c9ebfc2 100644
--- a/net/sctp/sysctl.c
+++ b/net/sctp/sysctl.c
@@ -212,6 +212,15 @@ static struct ctl_table sctp_net_table[] = {
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec_minmax,
 		.extra1		= SYSCTL_ZERO,
+		.extra2		= &init_net.sctp.ps_retrans,
+	},
+	{
+		.procname	= "ps_retrans",
+		.data		= &init_net.sctp.ps_retrans,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= &init_net.sctp.pf_retrans,
 		.extra2		= SYSCTL_INT_MAX,
 	},
 	{
-- 
2.1.0

[PATCH net-next 5/5] sctp: add spt_pathcpthld in struct sctp_paddrthlds

[Xin Long]

Section 7.2 of rfc7829: "Peer Address Thresholds (SCTP_PEER_ADDR_THLDS)
Socket Option" extends 'struct sctp_paddrthlds' with 'spt_pathcpthld'
added to allow a user to change ps_retrans per sock/asoc/transport, as
other 2 paddrthlds: pf_retrans, pathmaxrxt.

Note that ps_retrans is not allowed to be greater than pf_retrans.

Signed-off-by: Xin Long <lucien.xin@gmail.com>
---
 include/uapi/linux/sctp.h |  1 +
 net/sctp/socket.c         | 10 ++++++++++
 2 files changed, 11 insertions(+)

diff --git a/include/uapi/linux/sctp.h b/include/uapi/linux/sctp.h
index a15cc28..dfd81e1 100644
--- a/include/uapi/linux/sctp.h
+++ b/include/uapi/linux/sctp.h
@@ -1069,6 +1069,7 @@ struct sctp_paddrthlds {
 	struct sockaddr_storage spt_address;
 	__u16 spt_pathmaxrxt;
 	__u16 spt_pathpfthld;
+	__u16 spt_pathcpthld;
 };
 
 /*
diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index 5e2098b..5b9774d 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -3954,6 +3954,9 @@ static int sctp_setsockopt_paddr_thresholds(struct sock *sk,
 			   sizeof(struct sctp_paddrthlds)))
 		return -EFAULT;
 
+	if (val.spt_pathpfthld > val.spt_pathcpthld)
+		return -EINVAL;
+
 	if (!sctp_is_any(sk, (const union sctp_addr *)&val.spt_address)) {
 		trans = sctp_addr_id2transport(sk, &val.spt_address,
 					       val.spt_assoc_id);
@@ -3963,6 +3966,7 @@ static int sctp_setsockopt_paddr_thresholds(struct sock *sk,
 		if (val.spt_pathmaxrxt)
 			trans->pathmaxrxt = val.spt_pathmaxrxt;
 		trans->pf_retrans = val.spt_pathpfthld;
+		trans->ps_retrans = val.spt_pathcpthld;
 
 		return 0;
 	}
@@ -3978,17 +3982,20 @@ static int sctp_setsockopt_paddr_thresholds(struct sock *sk,
 			if (val.spt_pathmaxrxt)
 				trans->pathmaxrxt = val.spt_pathmaxrxt;
 			trans->pf_retrans = val.spt_pathpfthld;
+			trans->ps_retrans = val.spt_pathcpthld;
 		}
 
 		if (val.spt_pathmaxrxt)
 			asoc->pathmaxrxt = val.spt_pathmaxrxt;
 		asoc->pf_retrans = val.spt_pathpfthld;
+		asoc->ps_retrans = val.spt_pathcpthld;
 	} else {
 		struct sctp_sock *sp = sctp_sk(sk);
 
 		if (val.spt_pathmaxrxt)
 			sp->pathmaxrxt = val.spt_pathmaxrxt;
 		sp->pf_retrans = val.spt_pathpfthld;
+		sp->ps_retrans = val.spt_pathcpthld;
 	}
 
 	return 0;
@@ -7232,6 +7239,7 @@ static int sctp_getsockopt_paddr_thresholds(struct sock *sk,
 		if (!trans)
 			return -ENOENT;
 
+		val.spt_pathcpthld = trans->ps_retrans;
 		val.spt_pathmaxrxt = trans->pathmaxrxt;
 		val.spt_pathpfthld = trans->pf_retrans;
 
@@ -7244,11 +7252,13 @@ static int sctp_getsockopt_paddr_thresholds(struct sock *sk,
 		return -EINVAL;
 
 	if (asoc) {
+		val.spt_pathcpthld = asoc->ps_retrans;
 		val.spt_pathpfthld = asoc->pf_retrans;
 		val.spt_pathmaxrxt = asoc->pathmaxrxt;
 	} else {
 		struct sctp_sock *sp = sctp_sk(sk);
 
+		val.spt_pathcpthld = sp->ps_retrans;
 		val.spt_pathpfthld = sp->pf_retrans;
 		val.spt_pathmaxrxt = sp->pathmaxrxt;
 	}
-- 
2.1.0

RE: [PATCH net-next 5/5] sctp: add spt_pathcpthld in struct sctp_paddrthlds

[David Laight]

From: Xin Long
> Sent: 09 September 2019 08:57
> Section 7.2 of rfc7829: "Peer Address Thresholds (SCTP_PEER_ADDR_THLDS)
> Socket Option" extends 'struct sctp_paddrthlds' with 'spt_pathcpthld'
> added to allow a user to change ps_retrans per sock/asoc/transport, as
> other 2 paddrthlds: pf_retrans, pathmaxrxt.
> 
> Note that ps_retrans is not allowed to be greater than pf_retrans.
> 
> Signed-off-by: Xin Long <lucien.xin@gmail.com>
> ---
>  include/uapi/linux/sctp.h |  1 +
>  net/sctp/socket.c         | 10 ++++++++++
>  2 files changed, 11 insertions(+)
> 
> diff --git a/include/uapi/linux/sctp.h b/include/uapi/linux/sctp.h
> index a15cc28..dfd81e1 100644
> --- a/include/uapi/linux/sctp.h
> +++ b/include/uapi/linux/sctp.h
> @@ -1069,6 +1069,7 @@ struct sctp_paddrthlds {
>  	struct sockaddr_storage spt_address;
>  	__u16 spt_pathmaxrxt;
>  	__u16 spt_pathpfthld;
> +	__u16 spt_pathcpthld;
>  };
> 
>  /*
> diff --git a/net/sctp/socket.c b/net/sctp/socket.c
> index 5e2098b..5b9774d 100644
> --- a/net/sctp/socket.c
> +++ b/net/sctp/socket.c
> @@ -3954,6 +3954,9 @@ static int sctp_setsockopt_paddr_thresholds(struct sock *sk,

This code does:
	if (optlen < sizeof(struct sctp_paddrthlds))
		return -EINVAL;

So adding an extra field breaks existing application binaries
that use this option.

I've not checked the other patches or similar fubar.

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)

Re: [PATCH net-next 5/5] sctp: add spt_pathcpthld in struct sctp_paddrthlds

[David Miller]

From: Xin Long <lucien.xin@gmail.com>
Date: Mon,  9 Sep 2019 15:56:51 +0800

> diff --git a/include/uapi/linux/sctp.h b/include/uapi/linux/sctp.h
> index a15cc28..dfd81e1 100644
> --- a/include/uapi/linux/sctp.h
> +++ b/include/uapi/linux/sctp.h
> @@ -1069,6 +1069,7 @@ struct sctp_paddrthlds {
>  	struct sockaddr_storage spt_address;
>  	__u16 spt_pathmaxrxt;
>  	__u16 spt_pathpfthld;
> +	__u16 spt_pathcpthld;
>  };
>  
>  /*

As pointed out you can't add things to this structure without breaking existing
binaries.

Re: [PATCH net-next 5/5] sctp: add spt_pathcpthld in struct sctp_paddrthlds

[Xin Long]

On Wed, Sep 11, 2019 at 1:27 AM David Miller <davem@davemloft.net> wrote:
>
> From: Xin Long <lucien.xin@gmail.com>
> Date: Mon,  9 Sep 2019 15:56:51 +0800
>
> > diff --git a/include/uapi/linux/sctp.h b/include/uapi/linux/sctp.h
> > index a15cc28..dfd81e1 100644
> > --- a/include/uapi/linux/sctp.h
> > +++ b/include/uapi/linux/sctp.h
> > @@ -1069,6 +1069,7 @@ struct sctp_paddrthlds {
> >       struct sockaddr_storage spt_address;
> >       __u16 spt_pathmaxrxt;
> >       __u16 spt_pathpfthld;
> > +     __u16 spt_pathcpthld;
> >  };
> >
> >  /*
>
> As pointed out you can't add things to this structure without breaking existing
> binaries.
we had the same problem when adding:
spp_ipv6_flowlabel and spp_dscp into struct sctp_paddrparams. in:

commit 0b0dce7a36fb9f1a9dd8245ea82d3a268c6943fe
Author: Xin Long <lucien.xin@gmail.com>
Date:   Mon Jul 2 18:21:13 2018 +0800

    sctp: add spp_ipv6_flowlabel and spp_dscp for sctp_paddrparams

the solution was:

        if (optlen == sizeof(params)) {
                if (copy_from_user(&params, optval, optlen))
                        return -EFAULT;
        } else if (optlen == ALIGN(offsetof(struct sctp_paddrparams,
                                            spp_ipv6_flowlabel), 4)) {
                if (copy_from_user(&params, optval, optlen))
                        return -EFAULT;
                if (params.spp_flags & (SPP_DSCP | SPP_IPV6_FLOWLABEL))
                        return -EINVAL;
        } else {
                return -EINVAL;
        }

I will do the same for this patch. Thanks.

Re: [PATCH net-next 5/5] sctp: add spt_pathcpthld in struct sctp_paddrthlds

[Xin Long]

On Tue, Sep 10, 2019 at 9:19 PM David Laight <David.Laight@aculab.com> wrote:
>
> From: Xin Long
> > Sent: 09 September 2019 08:57
> > Section 7.2 of rfc7829: "Peer Address Thresholds (SCTP_PEER_ADDR_THLDS)
> > Socket Option" extends 'struct sctp_paddrthlds' with 'spt_pathcpthld'
> > added to allow a user to change ps_retrans per sock/asoc/transport, as
> > other 2 paddrthlds: pf_retrans, pathmaxrxt.
> >
> > Note that ps_retrans is not allowed to be greater than pf_retrans.
> >
> > Signed-off-by: Xin Long <lucien.xin@gmail.com>
> > ---
> >  include/uapi/linux/sctp.h |  1 +
> >  net/sctp/socket.c         | 10 ++++++++++
> >  2 files changed, 11 insertions(+)
> >
> > diff --git a/include/uapi/linux/sctp.h b/include/uapi/linux/sctp.h
> > index a15cc28..dfd81e1 100644
> > --- a/include/uapi/linux/sctp.h
> > +++ b/include/uapi/linux/sctp.h
> > @@ -1069,6 +1069,7 @@ struct sctp_paddrthlds {
> >       struct sockaddr_storage spt_address;
> >       __u16 spt_pathmaxrxt;
> >       __u16 spt_pathpfthld;
> > +     __u16 spt_pathcpthld;
> >  };
> >
> >  /*
> > diff --git a/net/sctp/socket.c b/net/sctp/socket.c
> > index 5e2098b..5b9774d 100644
> > --- a/net/sctp/socket.c
> > +++ b/net/sctp/socket.c
> > @@ -3954,6 +3954,9 @@ static int sctp_setsockopt_paddr_thresholds(struct sock *sk,
>
> This code does:
>         if (optlen < sizeof(struct sctp_paddrthlds))
>                 return -EINVAL;
here will become:

        if (optlen >= sizeof(struct sctp_paddrthlds)) {
                optlen = sizeof(struct sctp_paddrthlds);
        } else if (optlen >= ALIGN(offsetof(struct sctp_paddrthlds,
                                            spt_pathcpthld), 4))
                optlen = ALIGN(offsetof(struct sctp_paddrthlds,
                                        spt_pathcpthld), 4);
                val.spt_pathcpthld = 0xffff;
        else {
                return -EINVAL;
        }

        if (copy_from_user(&val, (struct sctp_paddrthlds __user *)optval,
                           optlen))
                return -EFAULT;

in sctp_getsockopt_paddr_thresholds():

        if (len >= sizeof(struct sctp_paddrthlds))
                len = sizeof(struct sctp_paddrthlds);
        else if (len >= ALIGN(offsetof(struct sctp_paddrthlds,
                                       spt_pathcpthld), 4))
                len = ALIGN(offsetof(struct sctp_paddrthlds,
                                     spt_pathcpthld), 4);
        else
                return -EINVAL;

        if (copy_from_user(&val, (struct sctp_paddrthlds __user *)optval, len))
                return -EFAULT;

>
> So adding an extra field breaks existing application binaries
> that use this option.
>
> I've not checked the other patches or similar fubar.
>
>         David
>
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)
>

RE: [PATCH net-next 5/5] sctp: add spt_pathcpthld in struct sctp_paddrthlds

[David Laight]

From: Xin Long [mailto:lucien.xin@gmail.com]
> Sent: 11 September 2019 09:52
> On Tue, Sep 10, 2019 at 9:19 PM David Laight <David.Laight@aculab.com> wrote:
> >
> > From: Xin Long
> > > Sent: 09 September 2019 08:57
> > > Section 7.2 of rfc7829: "Peer Address Thresholds (SCTP_PEER_ADDR_THLDS)
> > > Socket Option" extends 'struct sctp_paddrthlds' with 'spt_pathcpthld'
> > > added to allow a user to change ps_retrans per sock/asoc/transport, as
> > > other 2 paddrthlds: pf_retrans, pathmaxrxt.
> > >
> > > Note that ps_retrans is not allowed to be greater than pf_retrans.
> > >
> > > Signed-off-by: Xin Long <lucien.xin@gmail.com>
> > > ---
> > >  include/uapi/linux/sctp.h |  1 +
> > >  net/sctp/socket.c         | 10 ++++++++++
> > >  2 files changed, 11 insertions(+)
> > >
> > > diff --git a/include/uapi/linux/sctp.h b/include/uapi/linux/sctp.h
> > > index a15cc28..dfd81e1 100644
> > > --- a/include/uapi/linux/sctp.h
> > > +++ b/include/uapi/linux/sctp.h
> > > @@ -1069,6 +1069,7 @@ struct sctp_paddrthlds {
> > >       struct sockaddr_storage spt_address;
> > >       __u16 spt_pathmaxrxt;
> > >       __u16 spt_pathpfthld;
> > > +     __u16 spt_pathcpthld;
> > >  };
> > >
> > >  /*
> > > diff --git a/net/sctp/socket.c b/net/sctp/socket.c
> > > index 5e2098b..5b9774d 100644
> > > --- a/net/sctp/socket.c
> > > +++ b/net/sctp/socket.c
> > > @@ -3954,6 +3954,9 @@ static int sctp_setsockopt_paddr_thresholds(struct sock *sk,
> >
> > This code does:
> >         if (optlen < sizeof(struct sctp_paddrthlds))
> >                 return -EINVAL;
> here will become:
> 
>         if (optlen >= sizeof(struct sctp_paddrthlds)) {
>                 optlen = sizeof(struct sctp_paddrthlds);
>         } else if (optlen >= ALIGN(offsetof(struct sctp_paddrthlds,
>                                             spt_pathcpthld), 4))
>                 optlen = ALIGN(offsetof(struct sctp_paddrthlds,
>                                         spt_pathcpthld), 4);
>                 val.spt_pathcpthld = 0xffff;
>         else {
>                 return -EINVAL;
>         }

Hmmm...
If the kernel has to default 'val.spt_pathcpthld = 0xffff'
then recompiling an existing application with the new uapi
header is going to lead to very unexpected behaviour.

The best you can hope for is that the application memset the
structure to zero.
But more likely it is 'random' on-stack data.

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)

Re: [PATCH net-next 5/5] sctp: add spt_pathcpthld in struct sctp_paddrthlds

[Xin Long]

On Wed, Sep 11, 2019 at 5:03 PM David Laight <David.Laight@aculab.com> wrote:
>
> From: Xin Long [mailto:lucien.xin@gmail.com]
> > Sent: 11 September 2019 09:52
> > On Tue, Sep 10, 2019 at 9:19 PM David Laight <David.Laight@aculab.com> wrote:
> > >
> > > From: Xin Long
> > > > Sent: 09 September 2019 08:57
> > > > Section 7.2 of rfc7829: "Peer Address Thresholds (SCTP_PEER_ADDR_THLDS)
> > > > Socket Option" extends 'struct sctp_paddrthlds' with 'spt_pathcpthld'
> > > > added to allow a user to change ps_retrans per sock/asoc/transport, as
> > > > other 2 paddrthlds: pf_retrans, pathmaxrxt.
> > > >
> > > > Note that ps_retrans is not allowed to be greater than pf_retrans.
> > > >
> > > > Signed-off-by: Xin Long <lucien.xin@gmail.com>
> > > > ---
> > > >  include/uapi/linux/sctp.h |  1 +
> > > >  net/sctp/socket.c         | 10 ++++++++++
> > > >  2 files changed, 11 insertions(+)
> > > >
> > > > diff --git a/include/uapi/linux/sctp.h b/include/uapi/linux/sctp.h
> > > > index a15cc28..dfd81e1 100644
> > > > --- a/include/uapi/linux/sctp.h
> > > > +++ b/include/uapi/linux/sctp.h
> > > > @@ -1069,6 +1069,7 @@ struct sctp_paddrthlds {
> > > >       struct sockaddr_storage spt_address;
> > > >       __u16 spt_pathmaxrxt;
> > > >       __u16 spt_pathpfthld;
> > > > +     __u16 spt_pathcpthld;
> > > >  };
> > > >
> > > >  /*
> > > > diff --git a/net/sctp/socket.c b/net/sctp/socket.c
> > > > index 5e2098b..5b9774d 100644
> > > > --- a/net/sctp/socket.c
> > > > +++ b/net/sctp/socket.c
> > > > @@ -3954,6 +3954,9 @@ static int sctp_setsockopt_paddr_thresholds(struct sock *sk,
> > >
> > > This code does:
> > >         if (optlen < sizeof(struct sctp_paddrthlds))
> > >                 return -EINVAL;
> > here will become:
> >
> >         if (optlen >= sizeof(struct sctp_paddrthlds)) {
> >                 optlen = sizeof(struct sctp_paddrthlds);
> >         } else if (optlen >= ALIGN(offsetof(struct sctp_paddrthlds,
> >                                             spt_pathcpthld), 4))
> >                 optlen = ALIGN(offsetof(struct sctp_paddrthlds,
> >                                         spt_pathcpthld), 4);
> >                 val.spt_pathcpthld = 0xffff;
> >         else {
> >                 return -EINVAL;
> >         }
>
> Hmmm...
> If the kernel has to default 'val.spt_pathcpthld = 0xffff'
> then recompiling an existing application with the new uapi
> header is going to lead to very unexpected behaviour.
>
> The best you can hope for is that the application memset the
> structure to zero.
> But more likely it is 'random' on-stack data.
0xffff is a value to disable the feature 'Primary Path Switchover'.
you're right that user might set it to zero unexpectly with their
old application rebuilt.

A safer way is to introduce "sysctl net.sctp.ps_retrans", it won't
matter if users set spt_pathcpthld properly when they're not aware
of this feature, like "sysctl net.sctp.pF_retrans". Looks better?

>
>         David
>
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)

Re: [PATCH net-next 5/5] sctp: add spt_pathcpthld in struct sctp_paddrthlds

[Xin Long]

On Wed, Sep 11, 2019 at 5:21 PM Xin Long <lucien.xin@gmail.com> wrote:
>
> On Wed, Sep 11, 2019 at 5:03 PM David Laight <David.Laight@aculab.com> wrote:
> >
> > From: Xin Long [mailto:lucien.xin@gmail.com]
> > > Sent: 11 September 2019 09:52
> > > On Tue, Sep 10, 2019 at 9:19 PM David Laight <David.Laight@aculab.com> wrote:
> > > >
> > > > From: Xin Long
> > > > > Sent: 09 September 2019 08:57
> > > > > Section 7.2 of rfc7829: "Peer Address Thresholds (SCTP_PEER_ADDR_THLDS)
> > > > > Socket Option" extends 'struct sctp_paddrthlds' with 'spt_pathcpthld'
> > > > > added to allow a user to change ps_retrans per sock/asoc/transport, as
> > > > > other 2 paddrthlds: pf_retrans, pathmaxrxt.
> > > > >
> > > > > Note that ps_retrans is not allowed to be greater than pf_retrans.
> > > > >
> > > > > Signed-off-by: Xin Long <lucien.xin@gmail.com>
> > > > > ---
> > > > >  include/uapi/linux/sctp.h |  1 +
> > > > >  net/sctp/socket.c         | 10 ++++++++++
> > > > >  2 files changed, 11 insertions(+)
> > > > >
> > > > > diff --git a/include/uapi/linux/sctp.h b/include/uapi/linux/sctp.h
> > > > > index a15cc28..dfd81e1 100644
> > > > > --- a/include/uapi/linux/sctp.h
> > > > > +++ b/include/uapi/linux/sctp.h
> > > > > @@ -1069,6 +1069,7 @@ struct sctp_paddrthlds {
> > > > >       struct sockaddr_storage spt_address;
> > > > >       __u16 spt_pathmaxrxt;
> > > > >       __u16 spt_pathpfthld;
> > > > > +     __u16 spt_pathcpthld;
> > > > >  };
> > > > >
> > > > >  /*
> > > > > diff --git a/net/sctp/socket.c b/net/sctp/socket.c
> > > > > index 5e2098b..5b9774d 100644
> > > > > --- a/net/sctp/socket.c
> > > > > +++ b/net/sctp/socket.c
> > > > > @@ -3954,6 +3954,9 @@ static int sctp_setsockopt_paddr_thresholds(struct sock *sk,
> > > >
> > > > This code does:
> > > >         if (optlen < sizeof(struct sctp_paddrthlds))
> > > >                 return -EINVAL;
> > > here will become:
> > >
> > >         if (optlen >= sizeof(struct sctp_paddrthlds)) {
> > >                 optlen = sizeof(struct sctp_paddrthlds);
> > >         } else if (optlen >= ALIGN(offsetof(struct sctp_paddrthlds,
> > >                                             spt_pathcpthld), 4))
> > >                 optlen = ALIGN(offsetof(struct sctp_paddrthlds,
> > >                                         spt_pathcpthld), 4);
> > >                 val.spt_pathcpthld = 0xffff;
> > >         else {
> > >                 return -EINVAL;
> > >         }
> >
> > Hmmm...
> > If the kernel has to default 'val.spt_pathcpthld = 0xffff'
> > then recompiling an existing application with the new uapi
> > header is going to lead to very unexpected behaviour.
> >
> > The best you can hope for is that the application memset the
> > structure to zero.
> > But more likely it is 'random' on-stack data.
> 0xffff is a value to disable the feature 'Primary Path Switchover'.
> you're right that user might set it to zero unexpectly with their
> old application rebuilt.
>
> A safer way is to introduce "sysctl net.sctp.ps_retrans", it won't
> matter if users set spt_pathcpthld properly when they're not aware
> of this feature, like "sysctl net.sctp.pF_retrans". Looks better?
Sorry for confusing,  "sysctl net.sctp.ps_retrans" is already there
(its value is 0xffff by default),
we just need to do this in sctp_setsockopt_paddr_thresholds():

        if (copy_from_user(&val, (struct sctp_paddrthlds __user *)optval,
                           optlen))
                return -EFAULT;

        if (sock_net(sk)->sctp.ps_retrans == 0xffff)
                val.spt_pathcpthld = 0xffff;

        if (val.spt_pathpfthld > val.spt_pathcpthld)
                return -EINVAL;

>
> >
> >         David
> >
> > -
> > Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> > Registration No: 1397386 (Wales)

Re: [PATCH net-next 5/5] sctp: add spt_pathcpthld in struct sctp_paddrthlds

[Marcelo Ricardo Leitner]

On Wed, Sep 11, 2019 at 05:38:33PM +0800, Xin Long wrote:
> On Wed, Sep 11, 2019 at 5:21 PM Xin Long <lucien.xin@gmail.com> wrote:
> >
> > On Wed, Sep 11, 2019 at 5:03 PM David Laight <David.Laight@aculab.com> wrote:
> > >
> > > From: Xin Long [mailto:lucien.xin@gmail.com]
> > > > Sent: 11 September 2019 09:52
> > > > On Tue, Sep 10, 2019 at 9:19 PM David Laight <David.Laight@aculab.com> wrote:
> > > > >
> > > > > From: Xin Long
> > > > > > Sent: 09 September 2019 08:57
> > > > > > Section 7.2 of rfc7829: "Peer Address Thresholds (SCTP_PEER_ADDR_THLDS)
> > > > > > Socket Option" extends 'struct sctp_paddrthlds' with 'spt_pathcpthld'
> > > > > > added to allow a user to change ps_retrans per sock/asoc/transport, as
> > > > > > other 2 paddrthlds: pf_retrans, pathmaxrxt.
> > > > > >
> > > > > > Note that ps_retrans is not allowed to be greater than pf_retrans.
> > > > > >
> > > > > > Signed-off-by: Xin Long <lucien.xin@gmail.com>
> > > > > > ---
> > > > > >  include/uapi/linux/sctp.h |  1 +
> > > > > >  net/sctp/socket.c         | 10 ++++++++++
> > > > > >  2 files changed, 11 insertions(+)
> > > > > >
> > > > > > diff --git a/include/uapi/linux/sctp.h b/include/uapi/linux/sctp.h
> > > > > > index a15cc28..dfd81e1 100644
> > > > > > --- a/include/uapi/linux/sctp.h
> > > > > > +++ b/include/uapi/linux/sctp.h
> > > > > > @@ -1069,6 +1069,7 @@ struct sctp_paddrthlds {
> > > > > >       struct sockaddr_storage spt_address;
> > > > > >       __u16 spt_pathmaxrxt;
> > > > > >       __u16 spt_pathpfthld;
> > > > > > +     __u16 spt_pathcpthld;
> > > > > >  };
> > > > > >
> > > > > >  /*
> > > > > > diff --git a/net/sctp/socket.c b/net/sctp/socket.c
> > > > > > index 5e2098b..5b9774d 100644
> > > > > > --- a/net/sctp/socket.c
> > > > > > +++ b/net/sctp/socket.c
> > > > > > @@ -3954,6 +3954,9 @@ static int sctp_setsockopt_paddr_thresholds(struct sock *sk,
> > > > >
> > > > > This code does:
> > > > >         if (optlen < sizeof(struct sctp_paddrthlds))
> > > > >                 return -EINVAL;
> > > > here will become:
> > > >
> > > >         if (optlen >= sizeof(struct sctp_paddrthlds)) {
> > > >                 optlen = sizeof(struct sctp_paddrthlds);
> > > >         } else if (optlen >= ALIGN(offsetof(struct sctp_paddrthlds,
> > > >                                             spt_pathcpthld), 4))
> > > >                 optlen = ALIGN(offsetof(struct sctp_paddrthlds,
> > > >                                         spt_pathcpthld), 4);
> > > >                 val.spt_pathcpthld = 0xffff;
> > > >         else {
> > > >                 return -EINVAL;
> > > >         }
> > >
> > > Hmmm...
> > > If the kernel has to default 'val.spt_pathcpthld = 0xffff'
> > > then recompiling an existing application with the new uapi
> > > header is going to lead to very unexpected behaviour.
> > >
> > > The best you can hope for is that the application memset the
> > > structure to zero.
> > > But more likely it is 'random' on-stack data.
> > 0xffff is a value to disable the feature 'Primary Path Switchover'.
> > you're right that user might set it to zero unexpectly with their
> > old application rebuilt.
> >
> > A safer way is to introduce "sysctl net.sctp.ps_retrans", it won't
> > matter if users set spt_pathcpthld properly when they're not aware
> > of this feature, like "sysctl net.sctp.pF_retrans". Looks better?
> Sorry for confusing,  "sysctl net.sctp.ps_retrans" is already there
> (its value is 0xffff by default),
> we just need to do this in sctp_setsockopt_paddr_thresholds():
> 
>         if (copy_from_user(&val, (struct sctp_paddrthlds __user *)optval,
>                            optlen))
>                 return -EFAULT;
> 
>         if (sock_net(sk)->sctp.ps_retrans == 0xffff)
>                 val.spt_pathcpthld = 0xffff;

I'm confused with the snippets, but if I got them right, this is after
dealing with proper len and could leave val.spt_pathcpthld
uninitialized if the application used the old format and sysctl is !=
0xffff.

> 
>         if (val.spt_pathpfthld > val.spt_pathcpthld)
>                 return -EINVAL;
> 
> >
> > >
> > >         David
> > >
> > > -
> > > Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> > > Registration No: 1397386 (Wales)
> 

Re: [PATCH net-next 5/5] sctp: add spt_pathcpthld in struct sctp_paddrthlds

[Xin Long]

On Wed, Sep 11, 2019 at 8:56 PM Marcelo Ricardo Leitner
<marcelo.leitner@gmail.com> wrote:
>
> On Wed, Sep 11, 2019 at 05:38:33PM +0800, Xin Long wrote:
> > On Wed, Sep 11, 2019 at 5:21 PM Xin Long <lucien.xin@gmail.com> wrote:
> > >
> > > On Wed, Sep 11, 2019 at 5:03 PM David Laight <David.Laight@aculab.com> wrote:
> > > >
> > > > From: Xin Long [mailto:lucien.xin@gmail.com]
> > > > > Sent: 11 September 2019 09:52
> > > > > On Tue, Sep 10, 2019 at 9:19 PM David Laight <David.Laight@aculab.com> wrote:
> > > > > >
> > > > > > From: Xin Long
> > > > > > > Sent: 09 September 2019 08:57
> > > > > > > Section 7.2 of rfc7829: "Peer Address Thresholds (SCTP_PEER_ADDR_THLDS)
> > > > > > > Socket Option" extends 'struct sctp_paddrthlds' with 'spt_pathcpthld'
> > > > > > > added to allow a user to change ps_retrans per sock/asoc/transport, as
> > > > > > > other 2 paddrthlds: pf_retrans, pathmaxrxt.
> > > > > > >
> > > > > > > Note that ps_retrans is not allowed to be greater than pf_retrans.
> > > > > > >
> > > > > > > Signed-off-by: Xin Long <lucien.xin@gmail.com>
> > > > > > > ---
> > > > > > >  include/uapi/linux/sctp.h |  1 +
> > > > > > >  net/sctp/socket.c         | 10 ++++++++++
> > > > > > >  2 files changed, 11 insertions(+)
> > > > > > >
> > > > > > > diff --git a/include/uapi/linux/sctp.h b/include/uapi/linux/sctp.h
> > > > > > > index a15cc28..dfd81e1 100644
> > > > > > > --- a/include/uapi/linux/sctp.h
> > > > > > > +++ b/include/uapi/linux/sctp.h
> > > > > > > @@ -1069,6 +1069,7 @@ struct sctp_paddrthlds {
> > > > > > >       struct sockaddr_storage spt_address;
> > > > > > >       __u16 spt_pathmaxrxt;
> > > > > > >       __u16 spt_pathpfthld;
> > > > > > > +     __u16 spt_pathcpthld;
> > > > > > >  };
> > > > > > >
> > > > > > >  /*
> > > > > > > diff --git a/net/sctp/socket.c b/net/sctp/socket.c
> > > > > > > index 5e2098b..5b9774d 100644
> > > > > > > --- a/net/sctp/socket.c
> > > > > > > +++ b/net/sctp/socket.c
> > > > > > > @@ -3954,6 +3954,9 @@ static int sctp_setsockopt_paddr_thresholds(struct sock *sk,
> > > > > >
> > > > > > This code does:
> > > > > >         if (optlen < sizeof(struct sctp_paddrthlds))
> > > > > >                 return -EINVAL;
> > > > > here will become:
> > > > >
> > > > >         if (optlen >= sizeof(struct sctp_paddrthlds)) {
> > > > >                 optlen = sizeof(struct sctp_paddrthlds);
> > > > >         } else if (optlen >= ALIGN(offsetof(struct sctp_paddrthlds,
> > > > >                                             spt_pathcpthld), 4))
> > > > >                 optlen = ALIGN(offsetof(struct sctp_paddrthlds,
> > > > >                                         spt_pathcpthld), 4);
> > > > >                 val.spt_pathcpthld = 0xffff;
> > > > >         else {
> > > > >                 return -EINVAL;
> > > > >         }
> > > >
> > > > Hmmm...
> > > > If the kernel has to default 'val.spt_pathcpthld = 0xffff'
> > > > then recompiling an existing application with the new uapi
> > > > header is going to lead to very unexpected behaviour.
> > > >
> > > > The best you can hope for is that the application memset the
> > > > structure to zero.
> > > > But more likely it is 'random' on-stack data.
> > > 0xffff is a value to disable the feature 'Primary Path Switchover'.
> > > you're right that user might set it to zero unexpectly with their
> > > old application rebuilt.
> > >
> > > A safer way is to introduce "sysctl net.sctp.ps_retrans", it won't
> > > matter if users set spt_pathcpthld properly when they're not aware
> > > of this feature, like "sysctl net.sctp.pF_retrans". Looks better?
> > Sorry for confusing,  "sysctl net.sctp.ps_retrans" is already there
> > (its value is 0xffff by default),
> > we just need to do this in sctp_setsockopt_paddr_thresholds():
> >
> >         if (copy_from_user(&val, (struct sctp_paddrthlds __user *)optval,
> >                            optlen))
> >                 return -EFAULT;
> >
> >         if (sock_net(sk)->sctp.ps_retrans == 0xffff)
> >                 val.spt_pathcpthld = 0xffff;
>
> I'm confused with the snippets, but if I got them right, this is after
> dealing with proper len and could leave val.spt_pathcpthld
> uninitialized if the application used the old format and sysctl is !=
> 0xffff.
right, how about this in sctp_setsockopt_paddr_thresholds():

        offset = ALIGN(offsetof(struct sctp_paddrthlds, spt_pathcpthld), 4);
        if (optlen < offset)
                return -EINVAL;
        if (optlen < sizeof(val) || sock_net(sk)->sctp.ps_retrans == 0xffff) {
                optlen = offset;
                val.spt_pathcpthld = 0xffff;
        } else {
                optlen = sizeof(val);
        }

        if (copy_from_user(&val, (struct sctp_paddrthlds __user *)optval,
                           optlen))
                return -EFAULT;

        if (val.spt_pathpfthld > val.spt_pathcpthld)
                return -EINVAL;

Which means we will 'skip' spt_pathcpthld if (it's using old format) or
(ps_retrans is disabled and it's using new format).
Note that  ps_retrans < pf_retrans is not allowed in rfc7829.

and in sctp_getsockopt_paddr_thresholds():

        offset = ALIGN(offsetof(struct sctp_paddrthlds, spt_pathcpthld), 4);
        if (len < offset)
                return -EINVAL;
        if (len < sizeof(val) || sock_net(sk)->sctp.ps_retrans == 0xffff)
                len = offset;
        else
                len = sizeof(val);

        if (copy_from_user(&val, (struct sctp_paddrthlds __user *)optval, len))
                return -EFAULT;


>
> >
> >         if (val.spt_pathpfthld > val.spt_pathcpthld)
> >                 return -EINVAL;
> >
> > >
> > > >
> > > >         David
> > > >
> > > > -
> > > > Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> > > > Registration No: 1397386 (Wales)
> >

Re: [PATCH net-next 5/5] sctp: add spt_pathcpthld in struct sctp_paddrthlds

[Marcelo Ricardo Leitner]

On Thu, Sep 12, 2019 at 01:47:08AM +0800, Xin Long wrote:
> On Wed, Sep 11, 2019 at 8:56 PM Marcelo Ricardo Leitner
> <marcelo.leitner@gmail.com> wrote:
> >
> > On Wed, Sep 11, 2019 at 05:38:33PM +0800, Xin Long wrote:
> > > On Wed, Sep 11, 2019 at 5:21 PM Xin Long <lucien.xin@gmail.com> wrote:
> > > >
> > > > On Wed, Sep 11, 2019 at 5:03 PM David Laight <David.Laight@aculab.com> wrote:
> > > > >
> > > > > From: Xin Long [mailto:lucien.xin@gmail.com]
> > > > > > Sent: 11 September 2019 09:52
> > > > > > On Tue, Sep 10, 2019 at 9:19 PM David Laight <David.Laight@aculab.com> wrote:
> > > > > > >
> > > > > > > From: Xin Long
> > > > > > > > Sent: 09 September 2019 08:57
> > > > > > > > Section 7.2 of rfc7829: "Peer Address Thresholds (SCTP_PEER_ADDR_THLDS)
> > > > > > > > Socket Option" extends 'struct sctp_paddrthlds' with 'spt_pathcpthld'
> > > > > > > > added to allow a user to change ps_retrans per sock/asoc/transport, as
> > > > > > > > other 2 paddrthlds: pf_retrans, pathmaxrxt.
> > > > > > > >
> > > > > > > > Note that ps_retrans is not allowed to be greater than pf_retrans.
> > > > > > > >
> > > > > > > > Signed-off-by: Xin Long <lucien.xin@gmail.com>
> > > > > > > > ---
> > > > > > > >  include/uapi/linux/sctp.h |  1 +
> > > > > > > >  net/sctp/socket.c         | 10 ++++++++++
> > > > > > > >  2 files changed, 11 insertions(+)
> > > > > > > >
> > > > > > > > diff --git a/include/uapi/linux/sctp.h b/include/uapi/linux/sctp.h
> > > > > > > > index a15cc28..dfd81e1 100644
> > > > > > > > --- a/include/uapi/linux/sctp.h
> > > > > > > > +++ b/include/uapi/linux/sctp.h
> > > > > > > > @@ -1069,6 +1069,7 @@ struct sctp_paddrthlds {
> > > > > > > >       struct sockaddr_storage spt_address;
> > > > > > > >       __u16 spt_pathmaxrxt;
> > > > > > > >       __u16 spt_pathpfthld;
> > > > > > > > +     __u16 spt_pathcpthld;
> > > > > > > >  };
> > > > > > > >
> > > > > > > >  /*
> > > > > > > > diff --git a/net/sctp/socket.c b/net/sctp/socket.c
> > > > > > > > index 5e2098b..5b9774d 100644
> > > > > > > > --- a/net/sctp/socket.c
> > > > > > > > +++ b/net/sctp/socket.c
> > > > > > > > @@ -3954,6 +3954,9 @@ static int sctp_setsockopt_paddr_thresholds(struct sock *sk,
> > > > > > >
> > > > > > > This code does:
> > > > > > >         if (optlen < sizeof(struct sctp_paddrthlds))
> > > > > > >                 return -EINVAL;
> > > > > > here will become:
> > > > > >
> > > > > >         if (optlen >= sizeof(struct sctp_paddrthlds)) {
> > > > > >                 optlen = sizeof(struct sctp_paddrthlds);
> > > > > >         } else if (optlen >= ALIGN(offsetof(struct sctp_paddrthlds,
> > > > > >                                             spt_pathcpthld), 4))
> > > > > >                 optlen = ALIGN(offsetof(struct sctp_paddrthlds,
> > > > > >                                         spt_pathcpthld), 4);
> > > > > >                 val.spt_pathcpthld = 0xffff;
> > > > > >         else {
> > > > > >                 return -EINVAL;
> > > > > >         }
> > > > >
> > > > > Hmmm...
> > > > > If the kernel has to default 'val.spt_pathcpthld = 0xffff'
> > > > > then recompiling an existing application with the new uapi
> > > > > header is going to lead to very unexpected behaviour.
> > > > >
> > > > > The best you can hope for is that the application memset the
> > > > > structure to zero.
> > > > > But more likely it is 'random' on-stack data.
> > > > 0xffff is a value to disable the feature 'Primary Path Switchover'.
> > > > you're right that user might set it to zero unexpectly with their
> > > > old application rebuilt.
> > > >
> > > > A safer way is to introduce "sysctl net.sctp.ps_retrans", it won't
> > > > matter if users set spt_pathcpthld properly when they're not aware
> > > > of this feature, like "sysctl net.sctp.pF_retrans". Looks better?
> > > Sorry for confusing,  "sysctl net.sctp.ps_retrans" is already there
> > > (its value is 0xffff by default),
> > > we just need to do this in sctp_setsockopt_paddr_thresholds():
> > >
> > >         if (copy_from_user(&val, (struct sctp_paddrthlds __user *)optval,
> > >                            optlen))
> > >                 return -EFAULT;
> > >
> > >         if (sock_net(sk)->sctp.ps_retrans == 0xffff)
> > >                 val.spt_pathcpthld = 0xffff;
> >
> > I'm confused with the snippets, but if I got them right, this is after
> > dealing with proper len and could leave val.spt_pathcpthld
> > uninitialized if the application used the old format and sysctl is !=
> > 0xffff.
> right, how about this in sctp_setsockopt_paddr_thresholds():
> 
>         offset = ALIGN(offsetof(struct sctp_paddrthlds, spt_pathcpthld), 4);
>         if (optlen < offset)
>                 return -EINVAL;
>         if (optlen < sizeof(val) || sock_net(sk)->sctp.ps_retrans == 0xffff) {
>                 optlen = offset;
>                 val.spt_pathcpthld = 0xffff;
>         } else {
>                 optlen = sizeof(val);
>         }
> 
>         if (copy_from_user(&val, (struct sctp_paddrthlds __user *)optval,
>                            optlen))
>                 return -EFAULT;
> 
>         if (val.spt_pathpfthld > val.spt_pathcpthld)
>                 return -EINVAL;
> 
> Which means we will 'skip' spt_pathcpthld if (it's using old format) or
> (ps_retrans is disabled and it's using new format).

This will be inconsistent if we end up having to add another field
after spt_pathcpthld, because it will get ignored if ps_retrans ==
0xffff.  Lets not optimize out the fields please. This is already very
tricky to get right.

> Note that  ps_retrans < pf_retrans is not allowed in rfc7829.
> 
> and in sctp_getsockopt_paddr_thresholds():
> 
>         offset = ALIGN(offsetof(struct sctp_paddrthlds, spt_pathcpthld), 4);
>         if (len < offset)
>                 return -EINVAL;
>         if (len < sizeof(val) || sock_net(sk)->sctp.ps_retrans == 0xffff)
>                 len = offset;
>         else
>                 len = sizeof(val);

Here it is more visible. If net->...ps_retrans is disabled, remaining
fields (currently just this one, but as we are extending it now, we
have to think about the possibility of more as well) will be ignored,
we and we may not want that.

> 
>         if (copy_from_user(&val, (struct sctp_paddrthlds __user *)optval, len))
>                 return -EFAULT;
> 
> 
> >
> > >
> > >         if (val.spt_pathpfthld > val.spt_pathcpthld)
> > >                 return -EINVAL;
> > >
> > > >
> > > > >
> > > > >         David
> > > > >
> > > > > -
> > > > > Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> > > > > Registration No: 1397386 (Wales)
> > >
> 

RE: [PATCH net-next 5/5] sctp: add spt_pathcpthld in struct sctp_paddrthlds

[David Laight]

From: Marcelo Ricardo Leitner
> Sent: 12 September 2019 23:52
...
> Here it is more visible. If net->...ps_retrans is disabled, remaining
> fields (currently just this one, but as we are extending it now, we
> have to think about the possibility of more as well) will be ignored,
> we and we may not want that.

The only real way to add additional fields is to change the name
of the structure - that way recompiled programs still work.

You could require that programs zero the entire structure - but
that is difficult to verify.
And, in this case, it seems that the default has to be 0xffff
rather than 0 - which is, in itself, horrid.

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)

Re: [PATCH net-next 5/5] sctp: add spt_pathcpthld in struct sctp_paddrthlds

['Marcelo Ricardo Leitner']

On Fri, Sep 13, 2019 at 08:36:22AM +0000, David Laight wrote:
> From: Marcelo Ricardo Leitner
> > Sent: 12 September 2019 23:52
> ...
> > Here it is more visible. If net->...ps_retrans is disabled, remaining
> > fields (currently just this one, but as we are extending it now, we
> > have to think about the possibility of more as well) will be ignored,
> > we and we may not want that.
> 
> The only real way to add additional fields is to change the name
> of the structure - that way recompiled programs still work.
> 
> You could require that programs zero the entire structure - but
> that is difficult to verify.
> And, in this case, it seems that the default has to be 0xffff
> rather than 0 - which is, in itself, horrid.

Yep, and with that, a new sockopt as well. May not be the most
beautiful way, but it's the safest. Applications can then probe if the
sockopt is available or not and use what they want/can.

Inner kernel code can then be rearranged like it was for the peeloff
operation and peeloff + flags, and these issues just don't exist then.

We actually had agreed on using new sockopts, on thread
[PATCH net] sctp: make sctp_setsockopt_events() less strict about the option length

Interestingly, we have/had the opposite problem with netlink. Like, it
was allowing too much flexibility, such as silently ignoring unknown
fields (which is what would happen with a new app running on an older
kernel would trigger here) is bad because the app cannot know if it
was actually used or not. Some gymnastics in the app could cut through
the fat here, like probing getsockopt() return size, but then it may
as well probe for the right sockopt to be used.

  Marcelo

RE: [PATCH net-next 5/5] sctp: add spt_pathcpthld in struct sctp_paddrthlds

[David Laight]

From: 'Marcelo Ricardo Leitner'
> Sent: 13 September 2019 14:20
...
> Interestingly, we have/had the opposite problem with netlink. Like, it
> was allowing too much flexibility, such as silently ignoring unknown
> fields (which is what would happen with a new app running on an older
> kernel would trigger here) is bad because the app cannot know if it
> was actually used or not. Some gymnastics in the app could cut through
> the fat here, like probing getsockopt() return size, but then it may
> as well probe for the right sockopt to be used.

Yes, it would also work if the kernel checked that all 'unexpected'
fields were zero (up to some sanity limit of a few kB).

Then an application complied with a 'new' header would work with
an old kernel provided it didn't try so set any new fields.
(And it zeroed the entire structure.)

But you have to start off with that in mind.

Alternatively stop the insanity of setting multiple options
with one setsockopt call.
If multiple system calls are an issue implement a system call
that will set multiple options on the same socket.
(Maybe through a CMSG()-like buffer).
Then the application can set the ones it wants without having
to do the read-modify-write sequence needed for some of the
SCTP ones.

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)

Re: [PATCH net-next 5/5] sctp: add spt_pathcpthld in struct sctp_paddrthlds

['Marcelo Ricardo Leitner']

On Fri, Sep 13, 2019 at 01:31:22PM +0000, David Laight wrote:
> From: 'Marcelo Ricardo Leitner'
> > Sent: 13 September 2019 14:20
> ...
> > Interestingly, we have/had the opposite problem with netlink. Like, it
> > was allowing too much flexibility, such as silently ignoring unknown
> > fields (which is what would happen with a new app running on an older
> > kernel would trigger here) is bad because the app cannot know if it
> > was actually used or not. Some gymnastics in the app could cut through
> > the fat here, like probing getsockopt() return size, but then it may
> > as well probe for the right sockopt to be used.
> 
> Yes, it would also work if the kernel checked that all 'unexpected'
> fields were zero (up to some sanity limit of a few kB).

Though this would have to be done by older kernels, which are not
aware of this extra space by definition.

> 
> Then an application complied with a 'new' header would work with
> an old kernel provided it didn't try so set any new fields.
> (And it zeroed the entire structure.)
> 
> But you have to start off with that in mind.
> 
> Alternatively stop the insanity of setting multiple options
> with one setsockopt call.
> If multiple system calls are an issue implement a system call
> that will set multiple options on the same socket.
> (Maybe through a CMSG()-like buffer).
> Then the application can set the ones it wants without having
> to do the read-modify-write sequence needed for some of the
> SCTP ones.

I'm not sure I get you here. You mean we could have, for example, one
sockopt for each field on each struct we currently have? That would
bring other problems to the table, like how to deal with fields that
need to be updated together.

Anyhow, I'm afraid our hands a bit tied here. That's how the RFCs are
defining the interface and we shouldn't deviate too much from it.

What would help is that the RFC definited these versioned structs
itself.  Because as it is, even if we start versioning it, Linux will
have one versioning and other OSes will have another.

  Marcelo