Subject: Re: [PATCH net 1/2] xfrm6: Fix IPv6 payload_len in xfrm6_transport_finish

From: Steffen Klassert <[email-masked]>
Date: Wed, 21 Jun 2017 13:38:06 +0200

On Wed, Jun 21, 2017 at 11:24:05AM +0000, Yossi Kuperman wrote:
> 
> 
> > -----Original Message-----
> > From: Steffen Klassert [mailto:[email-masked]]
> > Sent: Wednesday, June 21, 2017 8:37 AM
> > To: Yossi Kuperman <[email-masked]>
> > Cc: [email-masked]; Herbert Xu <[email-masked]>;
> > Yevgeny Kliteynik <[email-masked]>; Boris Pismenny
> > <[email-masked]>; Ilan Tayari <[email-masked]>
> > Subject: Re: [PATCH net 1/2] xfrm6: Fix IPv6 payload_len in
> > xfrm6_transport_finish
> > 
> > On Mon, Jun 19, 2017 at 11:33:20AM +0300, [email-masked] wrote:
> > > From: Yossi Kuperman <[email-masked]>
> > >
> > > IPv6 payload length indicates the size of the payload, including any
> > > extension headers. In xfrm6_transport_finish,
> > > ipv6_hdr(skb)->payload_len is set to the payload size only, regardless
> > > of the presence of any extension headers.
> > >
> > > After ESP GRO transport mode decapsulation, ipv6_rcv trims the packet
> > > according to the wrong payload_len, thus corrupting the packet.
> > >
> > > Set payload_len to account for extension headers as well.
> > >
> > > Fixes: 716062fd4c2f ("[IPSEC]: Merge most of the input path")
> > > Signed-off-by: Yossi Kuperman <[email-masked]>
> > > ---
> > >  net/ipv6/xfrm6_input.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/net/ipv6/xfrm6_input.c b/net/ipv6/xfrm6_input.c index
> > > 08a807b..3ef5d91 100644
> > > --- a/net/ipv6/xfrm6_input.c
> > > +++ b/net/ipv6/xfrm6_input.c
> > > @@ -43,8 +43,8 @@ int xfrm6_transport_finish(struct sk_buff *skb, int
> > async)
> > >  		return 1;
> > >  #endif
> > >
> > > -	ipv6_hdr(skb)->payload_len = htons(skb->len);
> > >  	__skb_push(skb, skb->data - skb_network_header(skb));
> > > +	ipv6_hdr(skb)->payload_len = htons(skb->len - sizeof(struct
> > > +ipv6hdr));
> > 
> > You mentioned that the bug happens with ESP GRO. Does this bug also
> > happen in the standard codepath? If not, you might better move the above
> > line into the 'if' section below.
> > 
> 
> Yes, it happens only with ESP GRO.

In this case your Fixes tag is wrong.

> Normally, ipv6_rcv happens first which trims the packet correctly and then comes xfrm6_transport_finish.
> Now, with ESP GRO introduced, xfrm6_transport_finish, which comes first, modifies the packet's payload_len,
> and followed by a call to ipv6_rcv which trims it wrongly.
> 
> If I understand you right, you suggest to move the new line under the "if" section and restore the removed line?

I just want to make sure that the standard codepath works with this cange.
Did you test this with the standard codepath too?