[RFC net-next v2 04/18] netfilter: preserve IPv6 refragmentation state across reassembly
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WARM1d
From: Ralf Lici <ralf@mandelbit.com>
Date: 2026-10-24 09:26:15
Also in:
lkml, netfilter-devel
Subsystem:
networking [general], networking [ipv4/ipv6], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, David Ahern, Ido Schimmel, Linus Torvalds
Remember when all fragments describe a locally constructed IPv6 representation. Restore that state after conntrack reassembly so IPv6 output can fragment the datagram for its actual route without treating the old fragment size as a PMTU constraint. Signed-off-by: Ralf Lici <ralf@mandelbit.com> --- New patch in RFC v2. include/net/ipv6_frag.h | 2 ++ net/ipv6/netfilter/nf_conntrack_reasm.c | 11 ++++++++++- 2 files changed, 12 insertions(+), 1 deletion(-)
diff --git a/include/net/ipv6_frag.h b/include/net/ipv6_frag.h
index 41d9fc6965f9..df0a6309b342 100644
--- a/include/net/ipv6_frag.h
+++ b/include/net/ipv6_frag.h@@ -26,6 +26,7 @@ struct frag_queue { int iif; __u16 nhoffset; u8 ecn; + bool frag_source; }; #if IS_ENABLED(CONFIG_IPV6)
@@ -36,6 +37,7 @@ static inline void ip6frag_init(struct inet_frag_queue *q, const void *a) q->key.v6 = *key; fq->ecn = 0; + fq->frag_source = true; } static inline u32 ip6frag_key_hashfn(const void *data, u32 len, u32 seed)
diff --git a/net/ipv6/netfilter/nf_conntrack_reasm.c b/net/ipv6/netfilter/nf_conntrack_reasm.c
index be72c4346f8b..dee89aaf56ee 100644
--- a/net/ipv6/netfilter/nf_conntrack_reasm.c
+++ b/net/ipv6/netfilter/nf_conntrack_reasm.c@@ -272,6 +272,7 @@ static int nf_ct_frag6_queue(struct frag_queue *fq, struct sk_buff *skb, fq->q.tstamp_type = skb->tstamp_type; fq->q.meat += skb->len; fq->ecn |= ecn; + fq->frag_source &= !!(IP6CB(skb)->flags & IP6SKB_FRAG_SOURCE); if (payload_len > fq->q.max_size) fq->q.max_size = payload_len; add_frag_mem_limit(fq->q.fqdir, skb->truesize);
@@ -360,8 +361,16 @@ static int nf_ct_frag6_reasm(struct frag_queue *fq, struct sk_buff *skb, skb->dev = dev; ipv6_hdr(skb)->payload_len = htons(payload_len); ipv6_change_dsfield(ipv6_hdr(skb), 0xff, ecn); - IP6CB(skb)->frag_max_size = sizeof(struct ipv6hdr) + fq->q.max_size; IP6CB(skb)->flags |= IP6SKB_FRAGMENTED; + if (fq->frag_source) { + /* use the output route MTU instead of the old fragment size */ + IP6CB(skb)->frag_max_size = 0; + IP6CB(skb)->flags |= IP6SKB_FRAG_SOURCE; + } else { + IP6CB(skb)->frag_max_size = sizeof(struct ipv6hdr) + + fq->q.max_size; + IP6CB(skb)->flags &= ~IP6SKB_FRAG_SOURCE; + } /* Yes, and fold redundant checksum back. 8) */ if (skb->ip_summed == CHECKSUM_COMPLETE)
--
2.55.0