| Message ID | 20231220151544.270214-2-pablo@netfilter.org |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [net,1/2] netfilter: nf_tables: set transport offset from mac header for netdev/egress | expand |
diff --git a/include/net/netfilter/nf_tables_ipv4.h b/include/net/netfilter/nf_tables_ipv4.h index 947973623dc7..60a7d0ce3080 100644 --- a/include/net/netfilter/nf_tables_ipv4.h +++ b/include/net/netfilter/nf_tables_ipv4.h @@ -30,7 +30,7 @@ static inline int __nft_set_pktinfo_ipv4_validate(struct nft_pktinfo *pkt) return -1; len = iph_totlen(pkt->skb, iph); - thoff = iph->ihl * 4; + thoff = skb_network_offset(pkt->skb) + (iph->ihl * 4); if (pkt->skb->len < len) return -1; else if (len < thoff) diff --git a/net/netfilter/nf_tables_core.c b/net/netfilter/nf_tables_core.c index 8b536d7ef6c2..c3e635364701 100644 --- a/net/netfilter/nf_tables_core.c +++ b/net/netfilter/nf_tables_core.c @@ -158,7 +158,7 @@ static bool nft_payload_fast_eval(const struct nft_expr *expr, else { if (!(pkt->flags & NFT_PKTINFO_L4PROTO)) return false; - ptr = skb_network_header(skb) + nft_thoff(pkt); + ptr = skb->data + nft_thoff(pkt); } ptr += priv->offset;
Before this patch, transport offset (pkt->thoff) provides an offset relative to the network header. This is fine for the inet families because skb->data points to the network header in such case. However, from netdev/egress, skb->data points to the mac header (if available), thus, pkt->thoff is missing the mac header length. Add skb_network_offset() to the transport offset (pkt->thoff) for netdev, so transport header mangling works as expected. Adjust payload fast eval function to use skb->data now that pkt->thoff provides an absolute offset. This explains why users report that matching on egress/netdev works but payload mangling does not. This patch implicitly fixes payload mangling for IPv4 packets in netdev/egress given skb_store_bits() requires an offset from skb->data to reach the transport header. I suspect that nft_exthdr and the trace infra were also broken from netdev/egress because they also take skb->data as start, and pkt->thoff was not correct. Note that IPv6 is fine because ipv6_find_hdr() already provides a transport offset starting from skb->data, which includes skb_network_offset(). The bridge family also uses nft_set_pktinfo_ipv4_validate(), but there skb_network_offset() is zero, so the update in this patch does not alter the existing behaviour. Fixes: 42df6e1d221d ("netfilter: Introduce egress hook") Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org> --- include/net/netfilter/nf_tables_ipv4.h | 2 +- net/netfilter/nf_tables_core.c | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-)