[PATCH net-next v2 1/5] vxlan: vnifilter: reject VNIs outside the 24-bit space

[Ali Firas <alishmery18@gmail.com>]

VXLAN_VNIFILTER_ENTRY_START and VXLAN_VNIFILTER_ENTRY_END are declared as
bare NLA_U32, so neither is bounded before vxlan_process_vni_filter()
hands them to vxlan_vni_add_del():

	int v, err = 0;
	...
	for (v = start_vni; v <= end_vni; v++) {

v is int and end_vni is __u32, so the comparison is done unsigned. A
request carrying only START=0xffffffff gives vni_start == vni_end ==
0xffffffff, which looks like a single-VNI request. v is then -1,
"v <= end_vni" converts it to 0xffffffff and passes, v++ makes v 0, and
the loop walks the whole space upwards from there, allocating a VNI node
and a per-CPU stats block per iteration under rtnl_lock. Any range
ending at 0xffffffff behaves the same way, including narrow ones such as
START=0xfffff001 END=0xffffffff.

Separately, a VNI at or above VXLAN_N_VID is accepted and stored even
though the VXLAN header carries only 24 bits: vxlan_vni_field() shifts
without masking, so such an entry occupies its own rhashtable slot while
being truncated on the wire.

Range-validate both attributes against the 24-bit VNI space, which is
what vxlan_mdb.c already does for its own VNI attributes. The request is
then rejected during netlink policy validation, before
vxlan_process_vni_filter() is reached, and nothing is allocated. Make
the loop counter u32 while touching this: that is not what terminates
the loop, the policy check is, but it removes the signed overflow past
INT_MAX and matches the u32 vni parameter vxlan_vni_add() already takes.

Assisted-by: LLM
Signed-off-by: Ali Firas <alishmery18@gmail.com>
---
v1: https://lore.kernel.org/netdev/20260909092645.3105263-1-alishmery18@gmail.com/
 drivers/net/vxlan/vxlan_vnifilter.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/drivers/net/vxlan/vxlan_vnifilter.c b/drivers/net/vxlan/vxlan_vnifilter.c
index dd94085e0886..5aaaaeee8110 100644
--- a/drivers/net/vxlan/vxlan_vnifilter.c
+++ b/drivers/net/vxlan/vxlan_vnifilter.c
@@ -459,9 +459,15 @@ static int vxlan_vnifilter_dump(struct sk_buff *skb, struct netlink_callback *cb
 	return err;
 }
 
+static const struct netlink_range_validation vni_filter_vni_range = {
+	.max = VXLAN_N_VID - 1,
+};
+
 static const struct nla_policy vni_filter_entry_policy[VXLAN_VNIFILTER_ENTRY_MAX + 1] = {
-	[VXLAN_VNIFILTER_ENTRY_START] = { .type = NLA_U32 },
-	[VXLAN_VNIFILTER_ENTRY_END] = { .type = NLA_U32 },
+	[VXLAN_VNIFILTER_ENTRY_START] = NLA_POLICY_FULL_RANGE(NLA_U32,
+							      &vni_filter_vni_range),
+	[VXLAN_VNIFILTER_ENTRY_END] = NLA_POLICY_FULL_RANGE(NLA_U32,
+							    &vni_filter_vni_range),
 	[VXLAN_VNIFILTER_ENTRY_GROUP]	= NLA_POLICY_EXACT_LEN(sizeof_field(struct iphdr, daddr)),
 	[VXLAN_VNIFILTER_ENTRY_GROUP6]	= NLA_POLICY_EXACT_LEN(sizeof(struct in6_addr)),
 };
@@ -814,7 +820,8 @@ static int vxlan_vni_add_del(struct vxlan_dev *vxlan, __u32 start_vni,
 			     int cmd, struct netlink_ext_ack *extack)
 {
 	struct vxlan_vni_group *vg;
-	int v, err = 0;
+	int err = 0;
+	u32 v;
 
 	vg = rtnl_dereference(vxlan->vnigrp);
 
-- 
2.53.0