[PATCH net-next 11/11] netfilter: require Ethernet MAC header before using eth_hdr()

Florian Westphal
2026-04-10T11:24:45Z

From: Zhengchuan Liang <zcliangcn@gmail.com>

`ip6t_eui64`, `xt_mac`, the `bitmap:ip,mac`, `hash:ip,mac`, and
`hash:mac` ipset types, and `nf_log_syslog` access `eth_hdr(skb)`
after either assuming that the skb is associated with an Ethernet
device or checking only that the `ETH_HLEN` bytes at
`skb_mac_header(skb)` lie between `skb->head` and `skb->data`.

Make these paths first verify that the skb is associated with an
Ethernet device, that the MAC header was set, and that it spans at
least a full Ethernet header before accessing `eth_hdr(skb)`.

Suggested-by: Florian Westphal <fw@strlen.de>
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>
---
net/ipv6/netfilter/ip6t_eui64.c | 7 +++++--
net/netfilter/ipset/ip_set_bitmap_ipmac.c | 5 +++--
net/netfilter/ipset/ip_set_hash_ipmac.c | 9 +++++----
net/netfilter/ipset/ip_set_hash_mac.c | 5 +++--
net/netfilter/nf_log_syslog.c | 8 +++++++-
net/netfilter/xt_mac.c | 4 +---
6 files changed, 24 insertions(+), 14 deletions(-)

diff --git a/net/ipv6/netfilter/ip6t_eui64.c b/net/ipv6/netfilter/ip6t_eui64.c
index da69a27e8332..bbb684f9964c 100644
--- a/net/ipv6/netfilter/ip6t_eui64.c
+++ b/net/ipv6/netfilter/ip6t_eui64.c
@@ -7,6 +7,7 @@
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/ipv6.h>
+#include <linux/if_arp.h>
#include <linux/if_ether.h>

#include <linux/netfilter/x_tables.h>
@@ -21,8 +22,10 @@ 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)) {
+ if (!skb->dev || skb->dev->type != ARPHRD_ETHER)
+ return false;
+
+ if (!skb_mac_header_was_set(skb) || skb_mac_header_len(skb) < ETH_HLEN) {
par->hotdrop = true;
return false;
}
diff --git a/net/netfilter/ipset/ip_set_bitmap_ipmac.c b/net/netfilter/ipset/ip_set_bitmap_ipmac.c
index 2c625e0f49ec..752f59ef8744 100644
--- a/net/netfilter/ipset/ip_set_bitmap_ipmac.c
+++ b/net/netfilter/ipset/ip_set_bitmap_ipmac.c
@@ -11,6 +11,7 @@
#include <linux/etherdevice.h>
#include <linux/skbuff.h>
#include <linux/errno.h>
+#include <linux/if_arp.h>
#include <linux/if_ether.h>
#include <linux/netlink.h>
#include <linux/jiffies.h>
@@ -220,8 +221,8 @@ bitmap_ipmac_kadt(struct ip_set *set, const struct sk_buff *skb,
return -IPSET_ERR_BITMAP_RANGE;

/* Backward compatibility: we don't check the second flag */
- if (skb_mac_header(skb) < skb->head ||
- (skb_mac_header(skb) + ETH_HLEN) > skb->data)
+ if (!skb->dev || skb->dev->type != ARPHRD_ETHER ||
+ !skb_mac_header_was_set(skb) || skb_mac_header_len(skb) < ETH_HLEN)
return -EINVAL;

e.id = ip_to_id(map, ip);
diff --git a/net/netfilter/ipset/ip_set_hash_ipmac.c b/net/netfilter/ipset/ip_set_hash_ipmac.c
index 467c59a83c0a..b9a2681e2488 100644
--- a/net/netfilter/ipset/ip_set_hash_ipmac.c
+++ b/net/netfilter/ipset/ip_set_hash_ipmac.c
@@ -11,6 +11,7 @@
#include <linux/skbuff.h>
#include <linux/errno.h>
#include <linux/random.h>
+#include <linux/if_arp.h>
#include <linux/if_ether.h>
#include <net/ip.h>
#include <net/ipv6.h>
@@ -89,8 +90,8 @@ hash_ipmac4_kadt(struct ip_set *set, const struct sk_buff *skb,
struct hash_ipmac4_elem e = { .ip = 0, { .foo[0] = 0, .foo[1] = 0 } };
struct ip_set_ext ext = IP_SET_INIT_KEXT(skb, opt, set);

- if (skb_mac_header(skb) < skb->head ||
- (skb_mac_header(skb) + ETH_HLEN) > skb->data)
+ if (!skb->dev || skb->dev->type != ARPHRD_ETHER ||
+ !skb_mac_header_was_set(skb) || skb_mac_header_len(skb) < ETH_HLEN)
return -EINVAL;

if (opt->flags & IPSET_DIM_TWO_SRC)
@@ -205,8 +206,8 @@ hash_ipmac6_kadt(struct ip_set *set, const struct sk_buff *skb,
};
struct ip_set_ext ext = IP_SET_INIT_KEXT(skb, opt, set);

- if (skb_mac_header(skb) < skb->head ||
- (skb_mac_header(skb) + ETH_HLEN) > skb->data)
+ if (!skb->dev || skb->dev->type != ARPHRD_ETHER ||
+ !skb_mac_header_was_set(skb) || skb_mac_header_len(skb) < ETH_HLEN)
return -EINVAL;

if (opt->flags & IPSET_DIM_TWO_SRC)
diff --git a/net/netfilter/ipset/ip_set_hash_mac.c b/net/netfilter/ipset/ip_set_hash_mac.c
index 718814730acf..41a122591fe2 100644
--- a/net/netfilter/ipset/ip_set_hash_mac.c
+++ b/net/netfilter/ipset/ip_set_hash_mac.c
@@ -8,6 +8,7 @@
#include <linux/etherdevice.h>
#include <linux/skbuff.h>
#include <linux/errno.h>
+#include <linux/if_arp.h>
#include <linux/if_ether.h>
#include <net/netlink.h>

@@ -77,8 +78,8 @@ hash_mac4_kadt(struct ip_set *set, const struct sk_buff *skb,
struct hash_mac4_elem e = { { .foo[0] = 0, .foo[1] = 0 } };
struct ip_set_ext ext = IP_SET_INIT_KEXT(skb, opt, set);

- if (skb_mac_header(skb) < skb->head ||
- (skb_mac_header(skb) + ETH_HLEN) > skb->data)
+ if (!skb->dev || skb->dev->type != ARPHRD_ETHER ||
+ !skb_mac_header_was_set(skb) || skb_mac_header_len(skb) < ETH_HLEN)
return -EINVAL;

if (opt->flags & IPSET_DIM_ONE_SRC)
diff --git a/net/netfilter/nf_log_syslog.c b/net/netfilter/nf_log_syslog.c
index 0507d67cad27..7a8952b049d1 100644
--- a/net/netfilter/nf_log_syslog.c
+++ b/net/netfilter/nf_log_syslog.c
@@ -78,7 +78,10 @@ dump_arp_packet(struct nf_log_buf *m,
else
logflags = NF_LOG_DEFAULT_MASK;

- if (logflags & NF_LOG_MACDECODE) {
+ if ((logflags & NF_LOG_MACDECODE) &&
+ skb->dev && skb->dev->type == ARPHRD_ETHER &&
+ skb_mac_header_was_set(skb) &&
+ skb_mac_header_len(skb) >= ETH_HLEN) {
nf_log_buf_add(m, "MACSRC=%pM MACDST=%pM ",
eth_hdr(skb)->h_source, eth_hdr(skb)->h_dest);
nf_log_dump_vlan(m, skb);
@@ -797,6 +800,9 @@ static void dump_mac_header(struct nf_log_buf *m,

switch (dev->type) {
case ARPHRD_ETHER:
+ if (!skb_mac_header_was_set(skb) || skb_mac_header_len(skb) < ETH_HLEN)
+ return;
+
nf_log_buf_add(m, "MACSRC=%pM MACDST=%pM ",
eth_hdr(skb)->h_source, eth_hdr(skb)->h_dest);
nf_log_dump_vlan(m, skb);
diff --git a/net/netfilter/xt_mac.c b/net/netfilter/xt_mac.c
index 81649da57ba5..4798cd2ca26e 100644
--- a/net/netfilter/xt_mac.c
+++ b/net/netfilter/xt_mac.c
@@ -29,9 +29,7 @@ static bool mac_mt(const struct sk_buff *skb, struct xt_action_param *par)

if (skb->dev == NULL || skb->dev->type != ARPHRD_ETHER)
return false;
- if (skb_mac_header(skb) < skb->head)
- return false;
- if (skb_mac_header(skb) + ETH_HLEN > skb->data)
+ if (!skb_mac_header_was_set(skb) || skb_mac_header_len(skb) < ETH_HLEN)
return false;
ret = ether_addr_equal(eth_hdr(skb)->h_source, info->srcaddr);
ret ^= info->invert;
--
2.52.0