sctp: add pf_expose per netns and sock and asoc

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 'enabled' in next patch.

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 'disabled', as said in section 7.3.

v1->v2:
  - Fix a build warning noticed by Nathan Chancellor.
v2->v3:
  - set pf_expose to UNUSED by default to keep compatible with old
    applications.
v3->v4:
  - add a new entry for pf_expose on ip-sysctl.txt, as Marcelo suggested.
  - change this patch to 1/5, and move sctp_assoc_control_transport
    change into 2/5, as Marcelo suggested.
  - use SCTP_PF_EXPOSE_UNSET instead of SCTP_PF_EXPOSE_UNUSED, and
    set SCTP_PF_EXPOSE_UNSET to 0 in enum, as Marcelo suggested.

Signed-off-by: Xin Long <lucien.xin@gmail.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/ip-sysctl.txt

@@ -2091,6 +2091,28 @@ pf_enable - INTEGER
 
 	Default: 1
 
+pf_expose - INTEGER
+	Unset or enable/disable pf (pf is short for potentially failed) state
+	exposure.  Applications can control the exposure of the PF path state
+	in the SCTP_PEER_ADDR_CHANGE event and the SCTP_GET_PEER_ADDR_INFO
+	sockopt.   When it's unset, no SCTP_PEER_ADDR_CHANGE event with
+	SCTP_ADDR_PF state will be sent and a SCTP_PF-state transport info
+	can be got via SCTP_GET_PEER_ADDR_INFO sockopt;  When it's enabled,
+	a SCTP_PEER_ADDR_CHANGE event will be sent for a transport becoming
+	SCTP_PF state and a SCTP_PF-state transport info can be got via
+	SCTP_GET_PEER_ADDR_INFO sockopt;  When it's diabled, no
+	SCTP_PEER_ADDR_CHANGE event will be sent and it returns -EACCES when
+	trying to get a SCTP_PF-state transport info via SCTP_GET_PEER_ADDR_INFO
+	sockopt.
+
+	0: Unset pf state exposure, Compatible with old applications.
+
+	1: Disable pf state exposure.
+
+	2: Enable pf state exposure.
+
+	Default: 0
+
 addip_noauth_enable - BOOLEAN
 	Dynamic Address Reconfiguration (ADD-IP) requires the use of
 	authentication to protect the operations of adding or removing new

include/net/netns/sctp.h

@@ -96,6 +96,14 @@ struct netns_sctp {
 	 */
 	int pf_enable;
 
+	/*
+	 * Disable Potentially-Failed state exposure, ignored by default
+	 * pf_expose	-  0  : compatible with old applications (by default)
+	 *		-  1  : disable pf state exposure
+	 *		-  2  : enable  pf state exposure
+	 */
+	int pf_expose;
+
 	/*
 	 * Policy for preforming sctp/socket accounting
 	 * 0   - do socket level accounting, all assocs share sk_sndbuf

include/net/sctp/constants.h

@@ -286,6 +286,16 @@ enum { SCTP_MAX_GABS = 16 };
 				 * functions simpler to write.
 				 */
 
+/* These are the values for pf exposure, UNUSED is to keep compatible with old
+ * applications by default.
+ */
+enum {
+	SCTP_PF_EXPOSE_UNSET,
+	SCTP_PF_EXPOSE_DISABLE,
+	SCTP_PF_EXPOSE_ENABLE,
+};
+#define SCTP_PF_EXPOSE_MAX	SCTP_PF_EXPOSE_ENABLE
+
 /* These return values describe the success or failure of a number of
  * routines which form the lower interface to SCTP_outqueue.
  */

include/net/sctp/structs.h

@@ -215,6 +215,7 @@ struct sctp_sock {
 	__u32 adaptation_ind;
 	__u32 pd_point;
 	__u16	nodelay:1,
+		pf_expose:2,
 		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:2,       /* Expose pf state? */
 	     force_delay:1;
 
 	__u8 strreset_enable;

include/uapi/linux/sctp.h

@@ -933,6 +933,7 @@ 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 */

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);

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;
 
+	/* Ignore pf exposure feature by default */
+	net->sctp.pf_expose = SCTP_PF_EXPOSE_UNSET;
+
 	/* Association.Max.Retrans  - 10 attempts
 	 * Path.Max.Retrans         - 5  attempts (per destination address)
 	 * Max.Init.Retransmits     - 8  attempts

net/sctp/socket.c

@@ -5041,6 +5041,7 @@ 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;
@@ -5521,8 +5522,16 @@ 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 == SCTP_PF_EXPOSE_DISABLE) {
+		retval = -EACCES;
+		goto out;
+	}
 
 	pinfo.spinfo_assoc_id = sctp_assoc2id(transport->asoc);
 	pinfo.spinfo_state = transport->state;

net/sctp/sysctl.c

@@ -34,6 +34,7 @@ static int rto_alpha_min = 0;
 static int rto_beta_min = 0;
 static int rto_alpha_max = 1000;
 static int rto_beta_max = 1000;
+static int pf_expose_max = SCTP_PF_EXPOSE_MAX;
 
 static unsigned long max_autoclose_min = 0;
 static unsigned long max_autoclose_max =
@@ -318,6 +319,15 @@ 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_minmax,
+		.extra1		= SYSCTL_ZERO,
+		.extra2		= &pf_expose_max,
+	},
 
 	{ /* sentinel */ }
 };