path: root/iptables/xtables-arp.c
diff options
authorFlorian Westphal <>2018-11-05 17:51:18 +0100
committerFlorian Westphal <>2018-11-12 16:30:22 +0100
commit5aecb2d8bfdda4a6eea9d93079e33fc414afd8d0 (patch)
treeccedeeb94711207b6f7fbf81b9841a4a44ba0d19 /iptables/xtables-arp.c
parent9677ed12a93f165fa9840fd9f8fa183390a3bd04 (diff)
arptables: pre-init hlen and ethertype
to check -s, we need to add the size of the hardware address to the arp header to obtain the offset where the ipv4 address begins: base_arphdr HW_ADDR IP_ADDR (src) IP_ADDR (target) In arptables-classic, the kernel will add dev->addr_len to the arp header base address to obtain the correct location, but we cannot do this in nf_tables, at least not at this time (we need a fixed offset value). code does: op = nft_invflags2cmp(fw->arp.invflags, ARPT_INV_TGTIP); add_addr(r, sizeof(struct arphdr) + fw->arp.arhln + ... but if user did not provide "--h-length 6" argument, then this won't work even for ethernet, as the payload expression will be told to load the first 4 bytes of arp header source mac address (sender hw address). Fix this by pre-initialising arhlen to 6. We also need to set up arhrd. Otherwise, src/dst mac can't be used: arptables -A INPUT -i lo --destination-mac 11:22:33:44:55:66 arptables v1.8.1 (nf_tables): RULE_APPEND failed (Invalid argument): rule in chain INPUT This means that matching won't work for AX25, NETROM etc, however, arptables "classic" can't parse non-ethernet addresses, and makes ETH_ALEN assumptions in several spots, so this should be fine from compatibility point of view. Signed-off-by: Florian Westphal <>
Diffstat (limited to 'iptables/xtables-arp.c')
1 files changed, 2 insertions, 0 deletions
diff --git a/iptables/xtables-arp.c b/iptables/xtables-arp.c
index a791ecce..bde35e5d 100644
--- a/iptables/xtables-arp.c
+++ b/iptables/xtables-arp.c
@@ -905,6 +905,8 @@ int do_commandarp(struct nft_handle *h, int argc, char *argv[], char **table,
struct iptables_command_state cs = {
.jumpto = "",
+ .arp.arp.arhln = 6,
+ .arp.arp.arhrd = htons(ARPHRD_ETHER),
int invert = 0;
unsigned int nsaddrs = 0, ndaddrs = 0;