Re: [PATCH v14 nf-next 1/3] netfilter: utils: nf_checksum(_partial) correct data!=networkheader
From: Florian Westphal <fw@strlen.de>
Date: 2025-09-06 21:10:02
Also in:
bridge, netfilter-devel
Eric Woudstra [off-list ref] wrote:
quoted hunk ↗ jump to hunk
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;
skb_network_offset() ? And can you add a comment that tells why there is a need for pull/push pair despite the dataoff - nhpull argument?
+ DEBUG_NET_WARN_ON_ONCE(!skb_pointer_if_linear(skb, nhpull, 0));
maybe if (DEBUG_NET_WARN ... return 0 ?
quoted hunk ↗ jump to hunk
@@ -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);
Same here, but no need to copy the comment from nf_checksum, its enough to say something like "see nf_checksum()".