[PATCH net] vxlan: vnifilter: validate the VNI range in vni_filter_entry_policy

[Ali Firas <alishmery18@gmail.com>]

VXLAN_VNIFILTER_ENTRY_START and VXLAN_VNIFILTER_ENTRY_END are declared as
bare NLA_U32, so neither is range-checked before vxlan_process_vni_filter()
passes 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 unsigned. With
end_vni == U32_MAX the loop cannot terminate through its own condition:
v reaches U32_MAX, wraps to 0, and 0 <= U32_MAX is true again. Every
iteration allocates a vxlan_vni_node plus a per-CPU vxlan_vni_stats_pcpu
block until the machine is out of memory. Neither allocation carries
__GFP_ACCOUNT, so the memory is not charged to the caller's memory
cgroup, and the per-CPU block multiplies the cost by the number of CPUs.

The rtnl_msg_handler entry for RTM_NEWTUNNEL carries no
RTNL_FLAG_DOIT_UNLOCKED, so the loop runs holding rtnl_lock. rtnl_lock is
global rather than per-netns, so for as long as the loop runs every
network configuration operation on the host blocks, in every namespace.
There is no cond_resched() in the loop either.

The interface is reachable without privilege: creating the device and
adding VNIs only requires CAP_NET_ADMIN in the network namespace's user
namespace, so an unprivileged user inside unshare(CLONE_NEWUSER |
CLONE_NEWNET) can trigger this with a single netlink message.

A VNI at or above VXLAN_N_VID is also accepted and stored, although the
VXLAN header carries only 24 bits.

The MDB interface in the same driver already range-validates its VNI
attributes with an identical constraint (vxlan_mdb.c, vni_range with
.max = VXLAN_N_VID - 1). Apply the same validation here.

Tested under KASAN in a 2G guest: before the change, adding the range
0-U32_MAX from an unprivileged user namespace drives a global OOM with
the allocating task in vxlan_vnifilter_process(); after it, out-of-range
values are rejected and the in-range case is unaffected.

Reproducer available on request.

Fixes: f9c4bb0b245c ("vxlan: vni filtering support on collect metadata device")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4-6 [claude-code]
Signed-off-by: Ali Firas <alishmery18@gmail.com>
---
 drivers/net/vxlan/vxlan_vnifilter.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/net/vxlan/vxlan_vnifilter.c b/drivers/net/vxlan/vxlan_vnifilter.c
index dd94085e0886..9e86ac39cf9d 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)),
 };
-- 
2.53.0