From: Eric Woudstra <ericwouds@gmail.com>
To: Pablo Neira Ayuso <pablo@netfilter.org>,
Florian Westphal <fw@strlen.de>, Phil Sutter <phil@nwl.cc>,
Nikolay Aleksandrov <razor@blackwall.org>,
Ido Schimmel <idosch@nvidia.com>,
"David S. Miller" <davem@davemloft.net>,
Eric Dumazet <edumazet@google.com>,
Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
Simon Horman <horms@kernel.org>
Cc: netfilter-devel@vger.kernel.org, bridge@lists.linux.dev,
netdev@vger.kernel.org, Eric Woudstra <ericwouds@gmail.com>
Subject: [PATCH v20 nf-next 1/2] netfilter: utils: nf_ip(6)_checksum(_partial) correct data!=networkheader
Date: Tue, 12 May 2026 12:33:46 +0200 [thread overview]
Message-ID: <20260512103347.102746-2-ericwouds@gmail.com> (raw)
In-Reply-To: <20260512103347.102746-1-ericwouds@gmail.com>
In the conntrack hook it may not always be the case that:
skb_network_header(skb) == skb->data, i.e. skb_network_offset(skb)
is zero.
This is problematic when L4 function nf_conntrack_handle_packet(),
nf_conntrack_icmpv4/6_error() and other functions alike are accessing L3
data. These functions also calculate the checksum using
nf_ip(6)_checksum() and nf_ip(6)_checksum_partial().
They in turn use lower skb-checksum functions that are based on using
skb->data and will fail when skb_network_offset(skb) is not zero.
Adjust for skb_network_offset(skb), so that the checksum is calculated
correctly.
Signed-off-by: Eric Woudstra <ericwouds@gmail.com>
---
net/netfilter/utils.c | 52 ++++++++++++++++++++++++++++++++++++++-----
1 file changed, 46 insertions(+), 6 deletions(-)
diff --git a/net/netfilter/utils.c b/net/netfilter/utils.c
index 29c4dcc362c74..b738444c9cb6f 100644
--- a/net/netfilter/utils.c
+++ b/net/netfilter/utils.c
@@ -10,9 +10,18 @@
__sum16 nf_ip_checksum(struct sk_buff *skb, unsigned int hook,
unsigned int dataoff, u8 protocol)
{
+ unsigned int nhpull = skb_network_offset(skb);
const struct iphdr *iph = ip_hdr(skb);
__sum16 csum = 0;
+ if (WARN_ON_ONCE(!skb_pointer_if_linear(skb, nhpull, 0)))
+ return 0;
+
+ /* pull/push because the lower csum functions assume that
+ * skb_network_offset(skb) is zero.
+ */
+ dataoff -= nhpull;
+ __skb_pull(skb, nhpull);
switch (skb->ip_summed) {
case CHECKSUM_COMPLETE:
if (hook != NF_INET_PRE_ROUTING && hook != NF_INET_LOCAL_IN)
@@ -35,6 +44,7 @@ __sum16 nf_ip_checksum(struct sk_buff *skb, unsigned int hook,
protocol, 0);
csum = __skb_checksum_complete(skb);
}
+ __skb_push(skb, nhpull);
return csum;
}
EXPORT_SYMBOL(nf_ip_checksum);
@@ -44,29 +54,47 @@ static __sum16 nf_ip_checksum_partial(struct sk_buff *skb, unsigned int hook,
unsigned int dataoff, unsigned int len,
u8 protocol)
{
+ unsigned int nhpull = skb_network_offset(skb);
const struct iphdr *iph = ip_hdr(skb);
__sum16 csum = 0;
+ if (WARN_ON_ONCE(!skb_pointer_if_linear(skb, nhpull, 0)))
+ return 0;
+
+ /* See nf_ip_checksum() */
+ dataoff -= nhpull;
+ __skb_pull(skb, nhpull);
switch (skb->ip_summed) {
case CHECKSUM_COMPLETE:
- if (len == skb->len - dataoff)
- return nf_ip_checksum(skb, hook, dataoff, protocol);
+ if (len == skb->len - dataoff) {
+ csum = nf_ip_checksum(skb, hook, dataoff, protocol);
+ break;
+ }
fallthrough;
case CHECKSUM_NONE:
skb->csum = csum_tcpudp_nofold(iph->saddr, iph->daddr, protocol,
skb->len - dataoff, 0);
skb->ip_summed = CHECKSUM_NONE;
- return __skb_checksum_complete_head(skb, dataoff + len);
+ csum = __skb_checksum_complete_head(skb, dataoff + len);
+ break;
}
+ __skb_push(skb, nhpull);
return csum;
}
__sum16 nf_ip6_checksum(struct sk_buff *skb, unsigned int hook,
unsigned int dataoff, u8 protocol)
{
+ unsigned int nhpull = skb_network_offset(skb);
const struct ipv6hdr *ip6h = ipv6_hdr(skb);
__sum16 csum = 0;
+ if (WARN_ON_ONCE(!skb_pointer_if_linear(skb, nhpull, 0)))
+ return 0;
+
+ /* See nf_ip_checksum() */
+ dataoff -= nhpull;
+ __skb_pull(skb, nhpull);
switch (skb->ip_summed) {
case CHECKSUM_COMPLETE:
if (hook != NF_INET_PRE_ROUTING && hook != NF_INET_LOCAL_IN)
@@ -89,7 +117,9 @@ __sum16 nf_ip6_checksum(struct sk_buff *skb, unsigned int hook,
skb_checksum(skb, 0,
dataoff, 0))));
csum = __skb_checksum_complete(skb);
+ break;
}
+ __skb_push(skb, nhpull);
return csum;
}
EXPORT_SYMBOL(nf_ip6_checksum);
@@ -98,14 +128,23 @@ static __sum16 nf_ip6_checksum_partial(struct sk_buff *skb, unsigned int hook,
unsigned int dataoff, unsigned int len,
u8 protocol)
{
+ unsigned int nhpull = skb_network_offset(skb);
const struct ipv6hdr *ip6h = ipv6_hdr(skb);
__wsum hsum;
__sum16 csum = 0;
+ if (WARN_ON_ONCE(!skb_pointer_if_linear(skb, nhpull, 0)))
+ return 0;
+
+ /* See nf_ip_checksum() */
+ dataoff -= nhpull;
+ __skb_pull(skb, nhpull);
switch (skb->ip_summed) {
case CHECKSUM_COMPLETE:
- if (len == skb->len - dataoff)
- return nf_ip6_checksum(skb, hook, dataoff, protocol);
+ if (len == skb->len - dataoff) {
+ csum = nf_ip6_checksum(skb, hook, dataoff, protocol);
+ break;
+ }
fallthrough;
case CHECKSUM_NONE:
hsum = skb_checksum(skb, 0, dataoff, 0);
@@ -115,8 +154,9 @@ static __sum16 nf_ip6_checksum_partial(struct sk_buff *skb, unsigned int hook,
protocol,
csum_sub(0, hsum)));
skb->ip_summed = CHECKSUM_NONE;
- return __skb_checksum_complete_head(skb, dataoff + len);
+ csum = __skb_checksum_complete_head(skb, dataoff + len);
}
+ __skb_push(skb, nhpull);
return csum;
};
--
2.53.0
next prev parent reply other threads:[~2026-05-12 10:34 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-12 10:33 [PATCH v20 nf-next 0/2] conntrack: bridge: add double vlan, pppoe and pppoe-in-q Eric Woudstra
2026-05-12 10:33 ` Eric Woudstra [this message]
2026-05-12 10:33 ` [PATCH v20 nf-next 2/2] netfilter: bridge: Add conntrack double vlan and pppoe Eric Woudstra
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