[PATCH 6.18 101/198] netfilter: ip6t_eui64: reject invalid MAC header for all packets

Greg Kroah-Hartman
2026-04-20T16:01:38Z

From: Zhengchuan Liang <zcliangcn@gmail.com>

[ Upstream commit fdce0b3590f724540795b874b4c8850c90e6b0a8 ]

`eui64_mt6()` derives a modified EUI-64 from the Ethernet source address
and compares it with the low 64 bits of the IPv6 source address.

The existing guard only rejects an invalid MAC header when
`par->fragoff != 0`. For packets with `par->fragoff == 0`, `eui64_mt6()`
can still reach `eth_hdr(skb)` even when the MAC header is not valid.

Fix this by removing the `par->fragoff != 0` condition so that packets
with an invalid MAC header are rejected before accessing `eth_hdr(skb)`.

Fixes: 1da177e4c3f41 ("Linux-2.6.12-rc2")
Reported-by: Yifan Wu <yifanwucs@gmail.com>
Reported-by: Juefei Pu <tomapufckgml@gmail.com>
Co-developed-by: Yuan Tan <yuantan098@gmail.com>
Signed-off-by: Yuan Tan <yuantan098@gmail.com>
Suggested-by: Xin Liu <bird@lzu.edu.cn>
Tested-by: Ren Wei <enjou1224z@gmail.com>
Signed-off-by: Zhengchuan Liang <zcliangcn@gmail.com>
Signed-off-by: Ren Wei <n05ec@lzu.edu.cn>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/ipv6/netfilter/ip6t_eui64.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/net/ipv6/netfilter/ip6t_eui64.c b/net/ipv6/netfilter/ip6t_eui64.c
index d704f7ed300c2..da69a27e8332c 100644
--- a/net/ipv6/netfilter/ip6t_eui64.c
+++ b/net/ipv6/netfilter/ip6t_eui64.c
@@ -22,8 +22,7 @@ eui64_mt6(const struct sk_buff *skb, struct xt_action_param *par)
unsigned char eui64[8];

if (!(skb_mac_header(skb) >= skb->head &&
- skb_mac_header(skb) + ETH_HLEN <= skb->data) &&
- par->fragoff != 0) {
+ skb_mac_header(skb) + ETH_HLEN <= skb->data)) {
par->hotdrop = true;
return false;
}
--
2.53.0