Messages in this thread | | | Subject | Re: [PATCH v3] [net]: Fix skb->csum update in inet_proto_csum_replace16(). | From | Daniel Borkmann <> | Date | Wed, 22 Jan 2020 11:17:02 +0100 |
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On 11/6/19 11:52 PM, Praveen Chaudhary wrote: > skb->csum is updated incorrectly, when manipulation for NF_NAT_MANIP_SRC\DST > is done on IPV6 packet. > > Fix: > No need to update skb->csum in function inet_proto_csum_replace16(), even if > skb->ip_summed == CHECKSUM_COMPLETE, because change in L4 header checksum field > and change in IPV6 header cancels each other for skb->csum calculation. > > Signed-off-by: Praveen Chaudhary <pchaudhary@linkedin.com> > Signed-off-by: Zhenggen Xu <zxu@linkedin.com> > Signed-off-by: Andy Stracner <astracner@linkedin.com> > > Reviewed-by: Florian Westphal <fw@strlen.de> > --- > Changes in V2. > 1.) Updating diff as per email discussion with Florian Westphal. > Since inet_proto_csum_replace16() does incorrect calculation > for skb->csum in all cases. > 2.) Change in Commmit logs. > --- > > --- > Changes in V3. > Addressing Pablo`s Suggesion. > 1.) Updated Subject and description > 2.) Added full documentation of function. > --- > --- > net/core/utils.c | 18 +++++++++++++++--- > 1 file changed, 15 insertions(+), 3 deletions(-) > > diff --git a/net/core/utils.c b/net/core/utils.c > index 6b6e51d..af3b5cb 100644 > --- a/net/core/utils.c > +++ b/net/core/utils.c > @@ -438,6 +438,21 @@ void inet_proto_csum_replace4(__sum16 *sum, struct sk_buff *skb, > } > EXPORT_SYMBOL(inet_proto_csum_replace4); > > +/** > + * inet_proto_csum_replace16 - update L4 header checksum field as per the > + * update in IPv6 Header. Note, there is no need to update skb->csum in this > + * function, even if skb->ip_summed == CHECKSUM_COMPLETE, because change in L4 > + * header checksum field and change in IPV6 header cancels each other for > + * skb->csum calculation. > + * > + * @sum: L4 header checksum field > + * @skb: sk_buff for the packet > + * @from: old IPv6 address > + * @to: new IPv6 address > + * @pseudohdr: True if L4 header checksum includes pseudoheader > + * > + * Return void > + */ > void inet_proto_csum_replace16(__sum16 *sum, struct sk_buff *skb, > const __be32 *from, const __be32 *to, > bool pseudohdr) > @@ -449,9 +464,6 @@ void inet_proto_csum_replace16(__sum16 *sum, struct sk_buff *skb, > if (skb->ip_summed != CHECKSUM_PARTIAL) { > *sum = csum_fold(csum_partial(diff, sizeof(diff), > ~csum_unfold(*sum))); > - if (skb->ip_summed == CHECKSUM_COMPLETE && pseudohdr) > - skb->csum = ~csum_partial(diff, sizeof(diff), > - ~skb->csum);
What is the technical rationale in removing this here but not in any of the other inet_proto_csum_replace*() functions? You changelog has zero analysis on why here but not elsewhere this change would be needed?
> } else if (pseudohdr) > *sum = ~csum_fold(csum_partial(diff, sizeof(diff), > csum_unfold(*sum))); >
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