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netfilter: nf_tables: restore IP sanity checks for netdev/egress

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Subtract network offset to skb->len before performing IPv4 header sanity
checks, then adjust transport offset from offset from mac header.

Jorge Ortiz says:

When small UDP packets (< 4 bytes payload) are sent from eth0,
`meta l4proto udp` condition is not met because `NFT_PKTINFO_L4PROTO` is
not set. This happens because there is a comparison that checks if the
transport header offset exceeds the total length.  This comparison does
not take into account the fact that the skb network offset might be
non-zero in egress mode (e.g., 14 bytes for Ethernet header).

Fixes: 0ae8e4cca7 ("netfilter: nf_tables: set transport offset from mac header for netdev/egress")
Reported-by: Jorge Ortiz <jorge.ortiz.escribano@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Pablo Neira Ayuso 2024-08-26 12:45:22 +02:00
parent 8af174ea86
commit 5fd0628918
1 changed files with 6 additions and 4 deletions
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10
include/net/netfilter/nf_tables_ipv4.h
View File

@ -19,7 +19,7 @@ static inline void nft_set_pktinfo_ipv4(struct nft_pktinfo *pkt)
static inline int __nft_set_pktinfo_ipv4_validate(struct nft_pktinfo *pkt)
{
struct iphdr *iph, _iph;
u32 len, thoff;
u32 len, thoff, skb_len;
iph = skb_header_pointer(pkt->skb, skb_network_offset(pkt->skb),
sizeof(*iph), &_iph);
@ -30,8 +30,10 @@ static inline int __nft_set_pktinfo_ipv4_validate(struct nft_pktinfo *pkt)
return -1;
len = iph_totlen(pkt->skb, iph);
thoff = skb_network_offset(pkt->skb) + (iph->ihl * 4);
if (pkt->skb->len < len)
thoff = iph->ihl * 4;
skb_len = pkt->skb->len - skb_network_offset(pkt->skb);
if (skb_len < len)
return -1;
else if (len < thoff)
return -1;
@ -40,7 +42,7 @@ static inline int __nft_set_pktinfo_ipv4_validate(struct nft_pktinfo *pkt)
pkt->flags = NFT_PKTINFO_L4PROTO;
pkt->tprot = iph->protocol;
pkt->thoff = thoff;
pkt->thoff = skb_network_offset(pkt->skb) + thoff;
pkt->fragoff = ntohs(iph->frag_off) & IP_OFFSET;
return 0;