l2tp: add peer_offset parameter

Introduce peer_offset parameter in order to add the capability
to specify two different values for payload offset on tx/rx side.
If just offset is provided by userspace use it for rx side as well
in order to maintain compatibility with older l2tp versions

Signed-off-by: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/uapi/linux/l2tp.h

@@ -127,6 +127,7 @@ enum {
 	L2TP_ATTR_UDP_ZERO_CSUM6_TX,	/* flag */
 	L2TP_ATTR_UDP_ZERO_CSUM6_RX,	/* flag */
 	L2TP_ATTR_PAD,
+	L2TP_ATTR_PEER_OFFSET,		/* u16 */
 	__L2TP_ATTR_MAX,
 };
 

net/l2tp/l2tp_core.c

@@ -792,7 +792,7 @@ void l2tp_recv_common(struct l2tp_session *session, struct sk_buff *skb,
 			ptr += 2 + offset;
 		}
 	} else
-		ptr += session->offset;
+		ptr += session->peer_offset;
 
 	offset = ptr - optr;
 	if (!pskb_may_pull(skb, offset))
@@ -1785,6 +1785,7 @@ struct l2tp_session *l2tp_session_create(int priv_size, struct l2tp_tunnel *tunn
 			session->lns_mode = cfg->lns_mode;
 			session->reorder_timeout = cfg->reorder_timeout;
 			session->offset = cfg->offset;
+			session->peer_offset = cfg->peer_offset;
 			session->l2specific_type = cfg->l2specific_type;
 			session->l2specific_len = cfg->l2specific_len;
 			session->cookie_len = cfg->cookie_len;

net/l2tp/l2tp_core.h

@@ -59,7 +59,8 @@ struct l2tp_session_cfg {
 	int			debug;		/* bitmask of debug message
 						 * categories */
 	u16			vlan_id;	/* VLAN pseudowire only */
-	u16			offset;		/* offset to payload */
+	u16			offset;		/* offset to tx payload */
+	u16			peer_offset;	/* offset to rx payload */
 	u16			l2specific_len;	/* Layer 2 specific length */
 	u16			l2specific_type; /* Layer 2 specific type */
 	u8			cookie[8];	/* optional cookie */
@@ -86,8 +87,14 @@ struct l2tp_session {
 	int			cookie_len;
 	u8			peer_cookie[8];
 	int			peer_cookie_len;
-	u16			offset;		/* offset from end of L2TP header
+	u16			offset;		/* offset from end of L2TP
-						   to beginning of data */
+						 * header to beginning of
+						 * tx data
+						 */
+	u16			peer_offset;	/* offset from end of L2TP
+						 * header to beginning of
+						 * rx data
+						 */
 	u16			l2specific_len;
 	u16			l2specific_type;
 	u16			hdr_len;

net/l2tp/l2tp_debugfs.c

@@ -180,8 +180,9 @@ static void l2tp_dfs_seq_session_show(struct seq_file *m, void *v)
 		   session->lns_mode ? "LNS" : "LAC",
 		   session->debug,
 		   jiffies_to_msecs(session->reorder_timeout));
-	seq_printf(m, "   offset %hu l2specific %hu/%hu\n",
+	seq_printf(m, "   offset %hu peer_offset %hu l2specific %hu/%hu\n",
-		   session->offset, session->l2specific_type, session->l2specific_len);
+		   session->offset, session->peer_offset,
+		   session->l2specific_type, session->l2specific_len);
 	if (session->cookie_len) {
 		seq_printf(m, "   cookie %02x%02x%02x%02x",
 			   session->cookie[0], session->cookie[1],
@@ -228,7 +229,8 @@ static int l2tp_dfs_seq_show(struct seq_file *m, void *v)
 		seq_puts(m, " debug tx-pkts/bytes/errs rx-pkts/bytes/errs\n");
 		seq_puts(m, "  SESSION ID, peer ID, PWTYPE\n");
 		seq_puts(m, "   refcnt cnt\n");
-		seq_puts(m, "   offset OFFSET l2specific TYPE/LEN\n");
+		seq_puts(m, "   offset OFFSET peer_offset OFFSET");
+		seq_puts(m, " l2specific TYPE/LEN\n");
 		seq_puts(m, "   [ cookie ]\n");
 		seq_puts(m, "   [ peer cookie ]\n");
 		seq_puts(m, "   config mtu/mru/rcvseq/sendseq/dataseq/lns debug reorderto\n");

net/l2tp/l2tp_netlink.c

@@ -547,9 +547,25 @@ static int l2tp_nl_cmd_session_create(struct sk_buff *skb, struct genl_info *inf
 	}
 
 	if (tunnel->version > 2) {
-		if (info->attrs[L2TP_ATTR_OFFSET])
+		if (info->attrs[L2TP_ATTR_PEER_OFFSET]) {
+			struct nlattr *peer_offset;
+
+			peer_offset = info->attrs[L2TP_ATTR_PEER_OFFSET];
+			cfg.peer_offset = nla_get_u16(peer_offset);
+		}
+
+		if (info->attrs[L2TP_ATTR_OFFSET]) {
 			cfg.offset = nla_get_u16(info->attrs[L2TP_ATTR_OFFSET]);
 
+			/* in order to maintain compatibility with older
+			 * versions where offset was used for both tx and
+			 * rx side, update rx side with offset if peer_offset
+			 * is not provided by userspace
+			 */
+			if (!info->attrs[L2TP_ATTR_PEER_OFFSET])
+				cfg.peer_offset = cfg.offset;
+		}
+
 		if (info->attrs[L2TP_ATTR_DATA_SEQ])
 			cfg.data_seq = nla_get_u8(info->attrs[L2TP_ATTR_DATA_SEQ]);
 
@@ -763,6 +779,8 @@ static int l2tp_nl_session_send(struct sk_buff *skb, u32 portid, u32 seq, int fl
 	     nla_put_string(skb, L2TP_ATTR_IFNAME, session->ifname)) ||
 	    (session->offset &&
 	     nla_put_u16(skb, L2TP_ATTR_OFFSET, session->offset)) ||
+	    (session->peer_offset &&
+	     nla_put_u16(skb, L2TP_ATTR_PEER_OFFSET, session->peer_offset)) ||
 	    (session->cookie_len &&
 	     nla_put(skb, L2TP_ATTR_COOKIE, session->cookie_len,
 		     &session->cookie[0])) ||
@@ -903,6 +921,7 @@ static const struct nla_policy l2tp_nl_policy[L2TP_ATTR_MAX + 1] = {
 	[L2TP_ATTR_PW_TYPE]		= { .type = NLA_U16, },
 	[L2TP_ATTR_ENCAP_TYPE]		= { .type = NLA_U16, },
 	[L2TP_ATTR_OFFSET]		= { .type = NLA_U16, },
+	[L2TP_ATTR_PEER_OFFSET]		= { .type = NLA_U16, },
 	[L2TP_ATTR_DATA_SEQ]		= { .type = NLA_U8, },
 	[L2TP_ATTR_L2SPEC_TYPE]		= { .type = NLA_U8, },
 	[L2TP_ATTR_L2SPEC_LEN]		= { .type = NLA_U8, },