[PATCH v14 nf-next 1/3] netfilter: utils: nf_checksum(_partial) correct data!=networkheader
From: Eric Woudstra <hidden>
Date: 2025-07-08 15:12:27
Also in:
bridge, netfilter-devel
Subsystem:
netfilter, networking [general], the rest · Maintainers:
Pablo Neira Ayuso, Florian Westphal, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
In the conntrack hook it may not always be the case that: skb_network_header(skb) == skb->data. This is problematic when L4 function nf_conntrack_handle_packet() is accessing L3 data. This function uses thoff and ip_hdr() to finds it's data. But it also calculates the checksum. nf_checksum() and nf_checksum_partial() both use lower skb-checksum functions that are based on using skb->data. When skb_network_header(skb) != skb->data, adjust accordingly, so that the checksum is calculated correctly. Signed-off-by: Eric Woudstra <redacted> --- net/netfilter/utils.c | 20 ++++++++++++++------ 1 file changed, 14 insertions(+), 6 deletions(-)
diff --git a/net/netfilter/utils.c b/net/netfilter/utils.c
index 008419db815a..9ba822983bc0 100644
--- a/net/netfilter/utils.c
+++ b/net/netfilter/utils.c@@ -124,16 +124,20 @@ __sum16 nf_checksum(struct sk_buff *skb, unsigned int hook, unsigned int dataoff, u8 protocol, unsigned short family) { + unsigned int nhpull = skb_network_header(skb) - skb->data; __sum16 csum = 0; + DEBUG_NET_WARN_ON_ONCE(!skb_pointer_if_linear(skb, nhpull, 0)); + __skb_pull(skb, nhpull); switch (family) { case AF_INET: - csum = nf_ip_checksum(skb, hook, dataoff, protocol); + csum = nf_ip_checksum(skb, hook, dataoff - nhpull, protocol); break; case AF_INET6: - csum = nf_ip6_checksum(skb, hook, dataoff, protocol); + csum = nf_ip6_checksum(skb, hook, dataoff - nhpull, protocol); break; } + __skb_push(skb, nhpull); return csum; }
@@ -143,18 +147,22 @@ __sum16 nf_checksum_partial(struct sk_buff *skb, unsigned int hook, unsigned int dataoff, unsigned int len, u8 protocol, unsigned short family) { + unsigned int nhpull = skb_network_header(skb) - skb->data; __sum16 csum = 0; + DEBUG_NET_WARN_ON_ONCE(!skb_pointer_if_linear(skb, nhpull, 0)); + __skb_pull(skb, nhpull); switch (family) { case AF_INET: - csum = nf_ip_checksum_partial(skb, hook, dataoff, len, - protocol); + csum = nf_ip_checksum_partial(skb, hook, dataoff - nhpull, + len, protocol); break; case AF_INET6: - csum = nf_ip6_checksum_partial(skb, hook, dataoff, len, - protocol); + csum = nf_ip6_checksum_partial(skb, hook, dataoff - nhpull, + len, protocol); break; } + __skb_push(skb, nhpull); return csum; }
--
2.47.1