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: 0ae8e4cca787 ("netfilter: nf_tables: set transport offset from mac header for netdev/egress")
Reported-by: Jorge Ortiz <jorge.ortiz.escribano@xxxxxxxxx>
Signed-off-by: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
---
include/net/netfilter/nf_tables_ipv4.h | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)
diff --git a/include/net/netfilter/nf_tables_ipv4.h b/include/net/netfilter/nf_tables_ipv4.h
index 60a7d0ce3080..fcf967286e37 100644
--- a/include/net/netfilter/nf_tables_ipv4.h
+++ b/include/net/netfilter/nf_tables_ipv4.h
@@ -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;
--
2.30.2
