[PATCH net-next v3 3/6] vxlan: vnifilter: bound the number of VNIs one request may touch

@@ -17,6 +17,15 @@
 
 #include "vxlan_private.h"
 
+/* Maximum number of VNIs one RTM_NEWTUNNEL or RTM_DELTUNNEL message may add or
+ * delete, summed over all of its VXLAN_VNIFILTER_ENTRY attributes. VNI
+ * filtering is mainly used on bridged VXLAN devices where the VNI is derived
+ * from the VLAN, so one request touching more VNIs than the VLAN ID space has
+ * no practical use, while an unbounded request walks the 24-bit space one VNI
+ * at a time under rtnl_lock.
+ */
+#define VXLAN_VNI_FILTER_MSG_MAX	4096
+
 static inline int vxlan_vni_cmp(struct rhashtable_compare_arg *arg,
 				const void *ptr)
 {

@@ -846,12 +855,78 @@ static int vxlan_vni_add_del(struct vxlan_dev *vxlan, __u32 start_vni,
 	return err;
 }
 
+/* Derive the VNI range one VXLAN_VNIFILTER_ENTRY selects. Shared so that the
+ * count taken by vxlan_vnifilter_check_msg() cannot drift from the range
+ * vxlan_process_vni_filter() then acts on.
+ */
+static void vxlan_vni_filter_entry_range(struct nlattr **vattrs, u32 *vni_start,
+					 u32 *vni_end)
+{
+	*vni_start = 0;
+	*vni_end = 0;
+
+	if (vattrs[VXLAN_VNIFILTER_ENTRY_START]) {
+		*vni_start = nla_get_u32(vattrs[VXLAN_VNIFILTER_ENTRY_START]);
+		*vni_end = *vni_start;
+	}
+
+	if (vattrs[VXLAN_VNIFILTER_ENTRY_END])
+		*vni_end = nla_get_u32(vattrs[VXLAN_VNIFILTER_ENTRY_END]);
+}
+
+/* Reject a request touching more than VXLAN_VNI_FILTER_MSG_MAX VNIs before any
+ * of its entries is acted on. Both add and delete walk the span one VNI at a
+ * time under rtnl_lock, so both are bounded. Entries are applied one at a time
+ * and each one notifies as it goes, so a limit checked inside the dispatch loop
+ * would leave the entries ahead of the offending one already applied.
+ */
+static int vxlan_vnifilter_check_msg(const struct nlmsghdr *nlh,
+				     struct netlink_ext_ack *extack)
+{
+	struct nlattr *vattrs[VXLAN_VNIFILTER_ENTRY_MAX + 1];
+	struct nlattr *attr;
+	u32 vnis = 0;
+	int err, rem;
+
+	nlmsg_for_each_attr_type(attr, VXLAN_VNIFILTER_ENTRY, nlh,
+				 sizeof(struct tunnel_msg), rem) {
+		u32 vni_start, vni_end;
+
+		err = nla_parse_nested(vattrs, VXLAN_VNIFILTER_ENTRY_MAX, attr,
+				       vni_filter_entry_policy, extack);
+		if (err)
+			return err;
+
+		vxlan_vni_filter_entry_range(vattrs, &vni_start, &vni_end);
+
+		/* A start above the end selects no VNI and costs nothing;
+		 * leave it behaving as it does today.
+		 */
+		if (vni_end < vni_start)
+			continue;
+
+		/* vni_filter_entry_policy has already bounded both endpoints
+		 * below VXLAN_N_VID, so one entry adds at most VXLAN_N_VID and
+		 * vnis cannot wrap before the test below rejects it.
+		 */
+		vnis += vni_end - vni_start + 1;
+		if (vnis > VXLAN_VNI_FILTER_MSG_MAX) {
+			NL_SET_ERR_MSG_ATTR_FMT(extack, attr,
+						"Request asks for more than %u VNIs",
+						VXLAN_VNI_FILTER_MSG_MAX);
+			return -EINVAL;
+		}
+	}
+
+	return 0;
+}
+
 static int vxlan_process_vni_filter(struct vxlan_dev *vxlan,
 				    struct nlattr *nlvnifilter,
 				    int cmd, struct netlink_ext_ack *extack)
 {
 	struct nlattr *vattrs[VXLAN_VNIFILTER_ENTRY_MAX + 1];
-	u32 vni_start = 0, vni_end = 0;
+	u32 vni_start, vni_end;
 	union vxlan_addr group;
 	int err;
 

@@ -862,13 +937,7 @@ static int vxlan_process_vni_filter(struct vxlan_dev *vxlan,
 	if (err)
 		return err;
 
-	if (vattrs[VXLAN_VNIFILTER_ENTRY_START]) {
-		vni_start = nla_get_u32(vattrs[VXLAN_VNIFILTER_ENTRY_START]);
-		vni_end = vni_start;
-	}
-
-	if (vattrs[VXLAN_VNIFILTER_ENTRY_END])
-		vni_end = nla_get_u32(vattrs[VXLAN_VNIFILTER_ENTRY_END]);
+	vxlan_vni_filter_entry_range(vattrs, &vni_start, &vni_end);
 
 	if (!vni_start && !vni_end) {
 		NL_SET_ERR_MSG_ATTR(extack, nlvnifilter,

@@ -975,6 +1044,10 @@ static int vxlan_vnifilter_process(struct sk_buff *skb, struct nlmsghdr *nlh,
 	if (!(vxlan->cfg.flags & VXLAN_F_VNIFILTER))
 		return -EOPNOTSUPP;
 
+	err = vxlan_vnifilter_check_msg(nlh, extack);
+	if (err)
+		return err;
+
 	nlmsg_for_each_attr_type(attr, VXLAN_VNIFILTER_ENTRY, nlh,
 				 sizeof(*tmsg), rem) {
 		err = vxlan_process_vni_filter(vxlan, attr, nlh->nlmsg_type,