From 009d203e56dbe8db2589455b9e3644955f30313a Mon Sep 17 00:00:00 2001 From: Fernando Fernandez Mancera Date: Tue, 28 Apr 2026 12:25:47 +0200 Subject: [PATCH] netfilter: nf_tables: skip L4 header parsing for non-first fragments The tproxy, osf and exthdr (SCTP) expressions rely on the presence of transport layer headers to perform socket lookups, fingerprint matching, or chunk extraction. For fragmented packets, while the IP protocol remains constant across all fragments, only the first fragment contains the actual L4 header. The expressions could be attached to a chain with a priority lower than -400, bypassing defragmentation. Or could be used in stateless environments where defragmentation is not happening at all. This could result in garbage data being used for the matching. Add a check for pkt->fragoff so only unfragmented packets or the first fragment is processed. Fixes: 133dc203d77d ("netfilter: nft_exthdr: Support SCTP chunks") Fixes: 4ed8eb6570a4 ("netfilter: nf_tables: Add native tproxy support") Fixes: b96af92d6eaf ("netfilter: nf_tables: implement Passive OS fingerprint module in nft_osf") Signed-off-by: Fernando Fernandez Mancera Signed-off-by: Pablo Neira Ayuso --- net/netfilter/nf_tables_core.c | 2 +- net/netfilter/nft_exthdr.c | 2 +- net/netfilter/nft_osf.c | 2 +- net/netfilter/nft_tproxy.c | 8 ++++---- 4 files changed, 7 insertions(+), 7 deletions(-) diff --git a/net/netfilter/nf_tables_core.c b/net/netfilter/nf_tables_core.c index 5ddd5b6e135f1..8ab186f86dd43 100644 --- a/net/netfilter/nf_tables_core.c +++ b/net/netfilter/nf_tables_core.c @@ -153,7 +153,7 @@ static bool nft_payload_fast_eval(const struct nft_expr *expr, if (priv->base == NFT_PAYLOAD_NETWORK_HEADER) ptr = skb_network_header(skb) + pkt->nhoff; else { - if (!(pkt->flags & NFT_PKTINFO_L4PROTO)) + if (!(pkt->flags & NFT_PKTINFO_L4PROTO) || pkt->fragoff) return false; ptr = skb->data + nft_thoff(pkt); } diff --git a/net/netfilter/nft_exthdr.c b/net/netfilter/nft_exthdr.c index 0407d6f708ae9..e6a07c0df2079 100644 --- a/net/netfilter/nft_exthdr.c +++ b/net/netfilter/nft_exthdr.c @@ -376,7 +376,7 @@ static void nft_exthdr_sctp_eval(const struct nft_expr *expr, const struct sctp_chunkhdr *sch; struct sctp_chunkhdr _sch; - if (pkt->tprot != IPPROTO_SCTP) + if (pkt->tprot != IPPROTO_SCTP || pkt->fragoff) goto err; do { diff --git a/net/netfilter/nft_osf.c b/net/netfilter/nft_osf.c index c02d5cb52143b..45fe56da50442 100644 --- a/net/netfilter/nft_osf.c +++ b/net/netfilter/nft_osf.c @@ -33,7 +33,7 @@ static void nft_osf_eval(const struct nft_expr *expr, struct nft_regs *regs, return; } - if (pkt->tprot != IPPROTO_TCP) { + if (pkt->tprot != IPPROTO_TCP || pkt->fragoff) { regs->verdict.code = NFT_BREAK; return; } diff --git a/net/netfilter/nft_tproxy.c b/net/netfilter/nft_tproxy.c index f2101af8c867f..89be443734f66 100644 --- a/net/netfilter/nft_tproxy.c +++ b/net/netfilter/nft_tproxy.c @@ -30,8 +30,8 @@ static void nft_tproxy_eval_v4(const struct nft_expr *expr, __be16 tport = 0; struct sock *sk; - if (pkt->tprot != IPPROTO_TCP && - pkt->tprot != IPPROTO_UDP) { + if ((pkt->tprot != IPPROTO_TCP && + pkt->tprot != IPPROTO_UDP) || pkt->fragoff) { regs->verdict.code = NFT_BREAK; return; } @@ -97,8 +97,8 @@ static void nft_tproxy_eval_v6(const struct nft_expr *expr, memset(&taddr, 0, sizeof(taddr)); - if (pkt->tprot != IPPROTO_TCP && - pkt->tprot != IPPROTO_UDP) { + if ((pkt->tprot != IPPROTO_TCP && + pkt->tprot != IPPROTO_UDP) || pkt->fragoff) { regs->verdict.code = NFT_BREAK; return; } -- 2.47.3