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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org, greg@kroah.com
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Guillaume Nault <g.nault@alphalink.fr>,
        "David S. Miller" <davem@davemloft.net>,
        Giuliano Procida <gprocida@google.com>
Subject: [PATCH 4.9 39/64] l2tp: hold tunnel while handling genl tunnel updates
Date:   Tue, 26 May 2020 20:53:08 +0200
Message-Id: <20200526183926.219021493@linuxfoundation.org>
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From: Guillaume Nault <g.nault@alphalink.fr>

commit 8c0e421525c9eb50d68e8f633f703ca31680b746 upstream.

We need to make sure the tunnel is not going to be destroyed by
l2tp_tunnel_destruct() concurrently.

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>
Signed-off-by: Giuliano Procida <gprocida@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/l2tp/l2tp_netlink.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/net/l2tp/l2tp_netlink.c
+++ b/net/l2tp/l2tp_netlink.c
@@ -310,8 +310,8 @@ static int l2tp_nl_cmd_tunnel_modify(str
 	}
 	tunnel_id = nla_get_u32(info->attrs[L2TP_ATTR_CONN_ID]);
 
-	tunnel = l2tp_tunnel_find(net, tunnel_id);
-	if (tunnel == NULL) {
+	tunnel = l2tp_tunnel_get(net, tunnel_id);
+	if (!tunnel) {
 		ret = -ENODEV;
 		goto out;
 	}
@@ -322,6 +322,8 @@ static int l2tp_nl_cmd_tunnel_modify(str
 	ret = l2tp_tunnel_notify(&l2tp_nl_family, info,
 				 tunnel, L2TP_CMD_TUNNEL_MODIFY);
 
+	l2tp_tunnel_dec_refcount(tunnel);
+
 out:
 	return ret;
 }