sctp: add support for SCTP AUTH Information for sendmsg

This patch is to add support for SCTP AUTH Information for sendmsg,
as described in section 5.3.8 of RFC6458.

With this option, you can provide shared key identifier used for
sending the user message.

It's also a necessary send info for sctp_sendv.

Note that it reuses sinfo->sinfo_tsn to indicate if this option is
set and sinfo->sinfo_ssn to save the shkey ID which can be 0.
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/sctp/structs.h

@@ -2118,6 +2118,7 @@ struct sctp_cmsgs {
 	struct sctp_sndrcvinfo *srinfo;
 	struct sctp_sndinfo *sinfo;
 	struct sctp_prinfo *prinfo;
+	struct sctp_authinfo *authinfo;
 	struct msghdr *addrs_msg;
 };
 

include/uapi/linux/sctp.h

@@ -273,6 +273,18 @@ struct sctp_prinfo {
 	__u32 pr_value;
 };
 
+/* 5.3.8 SCTP AUTH Information Structure (SCTP_AUTHINFO)
+ *
+ *   This cmsghdr structure specifies SCTP options for sendmsg().
+ *
+ *   cmsg_level    cmsg_type      cmsg_data[]
+ *   ------------  ------------   -------------------
+ *   IPPROTO_SCTP  SCTP_AUTHINFO  struct sctp_authinfo
+ */
+struct sctp_authinfo {
+	__u16 auth_keynumber;
+};
+
 /*
  *  sinfo_flags: 16 bits (unsigned integer)
  *
@@ -310,7 +322,7 @@ typedef enum sctp_cmsg_type {
 #define SCTP_NXTINFO	SCTP_NXTINFO
 	SCTP_PRINFO,		/* 5.3.7 SCTP PR-SCTP Information Structure */
 #define SCTP_PRINFO	SCTP_PRINFO
-	SCTP_AUTHINFO,		/* 5.3.8 SCTP AUTH Information Structure (RESERVED) */
+	SCTP_AUTHINFO,		/* 5.3.8 SCTP AUTH Information Structure */
 #define SCTP_AUTHINFO	SCTP_AUTHINFO
 	SCTP_DSTADDRV4,		/* 5.3.9 SCTP Destination IPv4 Address Structure */
 #define SCTP_DSTADDRV4	SCTP_DSTADDRV4

net/sctp/chunk.c

@@ -206,8 +206,17 @@ struct sctp_datamsg *sctp_datamsg_from_user(struct sctp_association *asoc,
 			max_data -= SCTP_PAD4(sizeof(struct sctp_auth_chunk) +
 					      hmac_desc->hmac_len);
 
+		if (sinfo->sinfo_tsn &&
+		    sinfo->sinfo_ssn != asoc->active_key_id) {
+			shkey = sctp_auth_get_shkey(asoc, sinfo->sinfo_ssn);
+			if (!shkey) {
+				err = -EINVAL;
+				goto errout;
+			}
+		} else {
 			shkey = asoc->shkey;
 		}
+	}
 
 	/* Check what's our max considering the above */
 	max_data = min_t(size_t, max_data, asoc->frag_point);

net/sctp/socket.c

@@ -1987,6 +1987,14 @@ static void sctp_sendmsg_update_sinfo(struct sctp_association *asoc,
 
 	if (!cmsgs->srinfo && !cmsgs->prinfo)
 		sinfo->sinfo_timetolive = asoc->default_timetolive;
+
+	if (cmsgs->authinfo) {
+		/* Reuse sinfo_tsn to indicate that authinfo was set and
+		 * sinfo_ssn to save the keyid on tx path.
+		 */
+		sinfo->sinfo_tsn = 1;
+		sinfo->sinfo_ssn = cmsgs->authinfo->auth_keynumber;
+	}
 }
 
 static int sctp_sendmsg(struct sock *sk, struct msghdr *msg, size_t msg_len)
@@ -7874,6 +7882,21 @@ static int sctp_msghdr_parse(const struct msghdr *msg, struct sctp_cmsgs *cmsgs)
 			if (cmsgs->prinfo->pr_policy == SCTP_PR_SCTP_NONE)
 				cmsgs->prinfo->pr_value = 0;
 			break;
+		case SCTP_AUTHINFO:
+			/* SCTP Socket API Extension
+			 * 5.3.8 SCTP AUTH Information Structure (SCTP_AUTHINFO)
+			 *
+			 * This cmsghdr structure specifies SCTP options for sendmsg().
+			 *
+			 * cmsg_level    cmsg_type      cmsg_data[]
+			 * ------------  ------------   ---------------------
+			 * IPPROTO_SCTP  SCTP_AUTHINFO  struct sctp_authinfo
+			 */
+			if (cmsg->cmsg_len != CMSG_LEN(sizeof(struct sctp_authinfo)))
+				return -EINVAL;
+
+			cmsgs->authinfo = CMSG_DATA(cmsg);
+			break;
 		case SCTP_DSTADDRV4:
 		case SCTP_DSTADDRV6:
 			/* SCTP Socket API Extension