l2tp: hold tunnel used while creating sessions with netlink

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@alphalink.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 12 insertions, 9 deletions

diff --git a/net/l2tp/l2tp_netlink.c b/net/l2tp/l2tp_netlink.c
index ae5170e26281..57427d430f10 100644
--- a/net/l2tp/l2tp_netlink.c
+++ b/net/l2tp/l2tp_netlink.c
@@ -518,8 +518,9 @@ static int l2tp_nl_cmd_session_create(struct sk_buff *skb, struct genl_info *inf
                 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;
@@ -527,24 +528,24 @@ static int l2tp_nl_cmd_session_create(struct sk_buff *skb, struct genl_info *inf
 
         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) {
@@ -566,7 +567,7 @@ static int l2tp_nl_cmd_session_create(struct sk_buff *skb, struct genl_info *inf
                         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);
@@ -575,7 +576,7 @@ static int l2tp_nl_cmd_session_create(struct sk_buff *skb, struct genl_info *inf
                         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);
@@ -618,7 +619,7 @@ static int l2tp_nl_cmd_session_create(struct sk_buff *skb, struct genl_info *inf
         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 */
@@ -628,7 +629,7 @@ static int l2tp_nl_cmd_session_create(struct sk_buff *skb, struct genl_info *inf
         case L2TP_PWTYPE_ETH_VLAN:
                 if (!info->attrs[L2TP_ATTR_VLAN_ID]) {
                         ret = -EINVAL;
-                        goto out;
+                        goto out_tunnel;
                 }
                 break;
         case L2TP_PWTYPE_ETH:
@@ -656,6 +657,8 @@ static int l2tp_nl_cmd_session_create(struct sk_buff *skb, struct genl_info *inf
                 }
         }
 
+out_tunnel:
+        l2tp_tunnel_dec_refcount(tunnel);
 out:
         return ret;
 }