[PATCH net] vxlan: vnifilter: enforce exact length of GROUP/GROUP6 attributes

[Xiang Mei]

The VXLAN VNI filter entry policy declares the GROUP/GROUP6 address
attributes as NLA_BINARY with only a maximum length, so validate_nla()
accepts a payload shorter than the address. The GROUP consumer reads it
with nla_get_in_addr(), an unconditional 4-byte load, so a short
attribute over-reads up to 3 bytes of uninitialised slab data, which are
stored into remote_ip and echoed back via RTM_GETTUNNEL, disclosing
kernel memory.

Switch both entries to NLA_POLICY_EXACT_LEN() so the validator rejects
any GROUP/GROUP6 that is not exactly 4 / 16 bytes; a valid address is
always sent at full width.

Fixes: f9c4bb0b245c ("vxlan: vni filtering support on collect metadata device")
Reported-by: Weiming Shi <bestswngs@xxxxxxxxx>
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Xiang Mei <xmei5@xxxxxxx>
---
 drivers/net/vxlan/vxlan_vnifilter.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/net/vxlan/vxlan_vnifilter.c b/drivers/net/vxlan/vxlan_vnifilter.c
index 3e76f4e21094..dd94085e0886 100644
--- a/drivers/net/vxlan/vxlan_vnifilter.c
+++ b/drivers/net/vxlan/vxlan_vnifilter.c
@@ -462,10 +462,8 @@ static int vxlan_vnifilter_dump(struct sk_buff *skb, struct netlink_callback *cb
 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_GROUP]	= { .type = NLA_BINARY,
-					    .len = sizeof_field(struct iphdr, daddr) },
-	[VXLAN_VNIFILTER_ENTRY_GROUP6]	= { .type = NLA_BINARY,
-					    .len = sizeof(struct in6_addr) },
+	[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)),
 };
 
 static const struct nla_policy vni_filter_policy[VXLAN_VNIFILTER_MAX + 1] = {
-- 
2.43.0