[PATCH] net/openvswitch: fix trigger-able BUG_ON after ovs_vport_cmd_fill_info

[sunichi <sunyiqixm@gmail.com>]

ovs_vport_set_upcall_portids() does not validate the length of the
user-supplied OVS_VPORT_ATTR_UPCALL_PID netlink attribute. A
sufficiently large portid list can overflow the reply skb allocated
with NLMSG_DEFAULT_SIZE in causing ovs_vport_cmd_fill_info()
to return -EMSGSIZE and triggering the unconditional BUG_ON(),
which panics the kernel on most distributions.

Any local user with CAP_NET_ADMIN (or an equivalent unprivileged
namespace capability where applicable) can exploit this to perform a
denial-of-service against the host.

Replace BUG_ON with WARN_ON_ONCE to prevent kernel panic.

Signed-off-by: sunichi <sunyiqixm@gmail.com>
---
 net/openvswitch/datapath.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/net/openvswitch/datapath.c b/net/openvswitch/datapath.c
index e209099218b4..50c2945081a1 100644
--- a/net/openvswitch/datapath.c
+++ b/net/openvswitch/datapath.c
@@ -2202,7 +2202,8 @@ struct sk_buff *ovs_vport_cmd_build_info(struct vport *vport, struct net *net,
 
 	retval = ovs_vport_cmd_fill_info(vport, skb, net, portid, seq, 0, cmd,
 					 GFP_KERNEL);
-	BUG_ON(retval < 0);
+	if (WARN_ON_ONCE(retval < 0))
+		return ERR_PTR(-EMSGSIZE);
 
 	return skb;
 }
@@ -2358,7 +2359,9 @@ static int ovs_vport_cmd_new(struct sk_buff *skb, struct genl_info *info)
 	else
 		netdev_set_rx_headroom(vport->dev, dp->max_headroom);
 
-	BUG_ON(err < 0);
+	if (WARN_ON_ONCE(err < 0))
+		goto exit_unlock_free;
+
 	ovs_unlock();
 
 	ovs_notify(&dp_vport_genl_family, reply, info);
@@ -2411,7 +2414,8 @@ static int ovs_vport_cmd_set(struct sk_buff *skb, struct genl_info *info)
 	err = ovs_vport_cmd_fill_info(vport, reply, genl_info_net(info),
 				      info->snd_portid, info->snd_seq, 0,
 				      OVS_VPORT_CMD_SET, GFP_KERNEL);
-	BUG_ON(err < 0);
+	if (WARN_ON_ONCE(err < 0))
+		goto exit_unlock_free;
 
 	ovs_unlock();
 	ovs_notify(&dp_vport_genl_family, reply, info);
@@ -2451,7 +2455,8 @@ static int ovs_vport_cmd_del(struct sk_buff *skb, struct genl_info *info)
 	err = ovs_vport_cmd_fill_info(vport, reply, genl_info_net(info),
 				      info->snd_portid, info->snd_seq, 0,
 				      OVS_VPORT_CMD_DEL, GFP_KERNEL);
-	BUG_ON(err < 0);
+	if (WARN_ON_ONCE(err < 0))
+		goto exit_unlock_free;
 
 	/* the vport deletion may trigger dp headroom update */
 	dp = vport->dp;
@@ -2498,7 +2503,9 @@ static int ovs_vport_cmd_get(struct sk_buff *skb, struct genl_info *info)
 	err = ovs_vport_cmd_fill_info(vport, reply, genl_info_net(info),
 				      info->snd_portid, info->snd_seq, 0,
 				      OVS_VPORT_CMD_GET, GFP_ATOMIC);
-	BUG_ON(err < 0);
+	if (WARN_ON_ONCE(err < 0))
+		goto exit_unlock_free;
+
 	rcu_read_unlock();
 
 	return genlmsg_reply(reply, info);
-- 
2.34.1