[PATCH net-next 3/9] vxlan: vnifilter: use list_for_each_entry_rcu() in vxlan_vnifilter_dump_dev()

[Eric Dumazet <edumazet@google.com>]

vxlan_vnifilter_dump_dev() runs under rcu_read_lock() without RTNL when
dumping VNI filter entries via RTM_GETTUNNEL.

1) Currently it traverses vg->vni_list using list_for_each_entry_safe(),
   which performs raw pointer accesses without RCU dereference barriers.
   Since concurrent RTNL writers modify vg->vni_list using list_add_rcu()
   and list_del_rcu(), use list_for_each_entry_rcu() instead.

2) If vxlan_vnifilter_dump_dev() returns early because VXLAN_F_VNIFILTER
   is not set or vg has no VNIs, cb->args[1] was not cleared. If a
   paginated dump was in progress, this leaked a non-zero cb->args[1]
   to the next device in vxlan_vnifilter_dump(), silently skipping its
   first N VNIs. Clear cb->args[1] on early returns.

Fixes: f9c4bb0b245c ("vxlan: vni filtering support on collect metadata device")
Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 drivers/net/vxlan/vxlan_vnifilter.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/net/vxlan/vxlan_vnifilter.c b/drivers/net/vxlan/vxlan_vnifilter.c
index ddfa24ad16f9303d7796e4a199b16dd5cc62047c..53213542fa3ecf67d66ba6bf41f7ac51cf8fb471 100644
--- a/drivers/net/vxlan/vxlan_vnifilter.c
+++ b/drivers/net/vxlan/vxlan_vnifilter.c
@@ -333,7 +333,7 @@ static int vxlan_vnifilter_dump_dev(const struct net_device *dev,
 				    struct sk_buff *skb,
 				    struct netlink_callback *cb)
 {
-	struct vxlan_vni_node *tmp, *v, *vbegin = NULL, *vend = NULL;
+	struct vxlan_vni_node *v, *vbegin = NULL, *vend = NULL;
 	struct vxlan_dev *vxlan = netdev_priv(dev);
 	struct tunnel_msg *new_tmsg, *tmsg;
 	int idx = 0, s_idx = cb->args[1];
@@ -342,13 +342,17 @@ static int vxlan_vnifilter_dump_dev(const struct net_device *dev,
 	bool dump_stats;
 	int err = 0;
 
-	if (!(vxlan->cfg.flags & VXLAN_F_VNIFILTER))
+	if (!(vxlan->cfg.flags & VXLAN_F_VNIFILTER)) {
+		cb->args[1] = 0;
 		return -EINVAL;
+	}
 
 	/* RCU needed because of the vni locking rules (rcu || rtnl) */
 	vg = rcu_dereference(vxlan->vnigrp);
-	if (!vg || !vg->num_vnis)
+	if (!vg || !vg->num_vnis) {
+		cb->args[1] = 0;
 		return 0;
+	}
 
 	tmsg = nlmsg_data(cb->nlh);
 	dump_stats = !!(tmsg->flags & TUNNEL_MSG_FLAG_STATS);
@@ -362,7 +366,7 @@ static int vxlan_vnifilter_dump_dev(const struct net_device *dev,
 	new_tmsg->family = PF_BRIDGE;
 	new_tmsg->ifindex = dev->ifindex;
 
-	list_for_each_entry_safe(v, tmp, &vg->vni_list, vlist) {
+	list_for_each_entry_rcu(v, &vg->vni_list, vlist) {
 		if (idx < s_idx) {
 			idx++;
 			continue;
-- 
2.55.0.970.g62bdec98f9-goog