[PATCH 3.16 162/294] l2tp: hold tunnel used while creating sessions with netlink

[Ben Hutchings]

3.16.50-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Guillaume Nault <g.nault@xxxxxxxxxxxx>

commit e702c1204eb57788ef189c839c8c779368267d70 upstream.

Use l2tp_tunnel_get() to retrieve tunnel, so that it can't go away on
us. Otherwise l2tp_tunnel_destruct() might release the last reference
count concurrently, thus freeing the tunnel while we're using it.

Fixes: 309795f4bec2 ("l2tp: Add netlink control API for L2TP")
Signed-off-by: Guillaume Nault <g.nault@xxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 net/l2tp/l2tp_netlink.c | 21 ++++++++++++---------
 1 file changed, 12 insertions(+), 9 deletions(-)

--- a/net/l2tp/l2tp_netlink.c
+++ b/net/l2tp/l2tp_netlink.c
@@ -422,8 +422,9 @@ static int l2tp_nl_cmd_session_create(st
 		ret = -EINVAL;
 		goto out;
 	}
+
 	tunnel_id = nla_get_u32(info->attrs[L2TP_ATTR_CONN_ID]);
-	tunnel = l2tp_tunnel_find(net, tunnel_id);
+	tunnel = l2tp_tunnel_get(net, tunnel_id);
 	if (!tunnel) {
 		ret = -ENODEV;
 		goto out;
@@ -431,24 +432,24 @@ static int l2tp_nl_cmd_session_create(st
 
 	if (!info->attrs[L2TP_ATTR_SESSION_ID]) {
 		ret = -EINVAL;
-		goto out;
+		goto out_tunnel;
 	}
 	session_id = nla_get_u32(info->attrs[L2TP_ATTR_SESSION_ID]);
 
 	if (!info->attrs[L2TP_ATTR_PEER_SESSION_ID]) {
 		ret = -EINVAL;
-		goto out;
+		goto out_tunnel;
 	}
 	peer_session_id = nla_get_u32(info->attrs[L2TP_ATTR_PEER_SESSION_ID]);
 
 	if (!info->attrs[L2TP_ATTR_PW_TYPE]) {
 		ret = -EINVAL;
-		goto out;
+		goto out_tunnel;
 	}
 	cfg.pw_type = nla_get_u16(info->attrs[L2TP_ATTR_PW_TYPE]);
 	if (cfg.pw_type >= __L2TP_PWTYPE_MAX) {
 		ret = -EINVAL;
-		goto out;
+		goto out_tunnel;
 	}
 
 	if (tunnel->version > 2) {
@@ -470,7 +471,7 @@ static int l2tp_nl_cmd_session_create(st
 			u16 len = nla_len(info->attrs[L2TP_ATTR_COOKIE]);
 			if (len > 8) {
 				ret = -EINVAL;
-				goto out;
+				goto out_tunnel;
 			}
 			cfg.cookie_len = len;
 			memcpy(&cfg.cookie[0], nla_data(info->attrs[L2TP_ATTR_COOKIE]), len);
@@ -479,7 +480,7 @@ static int l2tp_nl_cmd_session_create(st
 			u16 len = nla_len(info->attrs[L2TP_ATTR_PEER_COOKIE]);
 			if (len > 8) {
 				ret = -EINVAL;
-				goto out;
+				goto out_tunnel;
 			}
 			cfg.peer_cookie_len = len;
 			memcpy(&cfg.peer_cookie[0], nla_data(info->attrs[L2TP_ATTR_PEER_COOKIE]), len);
@@ -515,7 +516,7 @@ static int l2tp_nl_cmd_session_create(st
 	if ((l2tp_nl_cmd_ops[cfg.pw_type] == NULL) ||
 	    (l2tp_nl_cmd_ops[cfg.pw_type]->session_create == NULL)) {
 		ret = -EPROTONOSUPPORT;
-		goto out;
+		goto out_tunnel;
 	}
 
 	/* Check that pseudowire-specific params are present */
@@ -525,7 +526,7 @@ static int l2tp_nl_cmd_session_create(st
 	case L2TP_PWTYPE_ETH_VLAN:
 		if (!info->attrs[L2TP_ATTR_VLAN_ID]) {
 			ret = -EINVAL;
-			goto out;
+			goto out_tunnel;
 		}
 		break;
 	case L2TP_PWTYPE_ETH:
@@ -544,6 +545,8 @@ static int l2tp_nl_cmd_session_create(st
 		ret = (*l2tp_nl_cmd_ops[cfg.pw_type]->session_create)(net, tunnel_id,
 			session_id, peer_session_id, &cfg);
 
+out_tunnel:
+	l2tp_tunnel_dec_refcount(tunnel);
 out:
 	return ret;
 }