David Woodhouse <[email protected]> wrote:
> On Wed, 2015-09-16 at 01:48 +0200, Florian Westphal wrote:
> >
> > What I don't understand is why you see this with fragmented ipv6
> > packets only (and not with all ipv6 forwarded skbs).
> >
> > Something like this copy-pastry from ip_finish_output2 should fix it:
>
> That works; thanks.
>
> Tested-by: David Woodhouse <[email protected]>
>
> A little extra debugging output shows that the offending fragments were
> arriving here with skb_headroom(skb)==10. Which is reasonable, being
> the Solos ADSL card's header of 8 bytes followed by 2 bytes of PPP
> frame type.
>
> The non-fragmented packets, on the other hand, are arriving with a
> headroom of 42 bytes. Could something else already have reallocated
> them before they get that far?
Yep. I missed
if (skb_cow(skb, dst->dev->hard_header_len)) {
call in ip6_forward().
Problem is of course that we only expand headroom of the skb
and not of the fragment(s) stored in that skbs frag list.
So we have several options for a fix.
- expand headroom in ip6_finish_output2, like we do for ipv4
- expand headroom in ip6_fragment
- defer to slowpath if frags don't have enough headroom.
The latter is the smallest patch and would not add test for locally
generated, non-fragmented skbs.
(not even compile tested)
David, could you test this? I'd do an official patch submission then.
diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -586,6 +586,7 @@ int ip6_fragment(struct sock *sk, struct sk_buff *skb,
frag_id = ipv6_select_ident(net, &ipv6_hdr(skb)->daddr,
&ipv6_hdr(skb)->saddr);
+ hroom = LL_RESERVED_SPACE(rt->dst.dev);
if (skb_has_frag_list(skb)) {
int first_len = skb_pagelen(skb);
struct sk_buff *frag2;
@@ -599,7 +600,7 @@ int ip6_fragment(struct sock *sk, struct sk_buff *skb,
/* Correct geometry. */
if (frag->len > mtu ||
((frag->len & 7) && frag->next) ||
- skb_headroom(frag) < hlen)
+ skb_headroom(frag) < (hlen + hroom))
goto slow_path_clean;
/* Partially cloned skb? */
@@ -724,7 +725,6 @@ slow_path:
*/
*prevhdr = NEXTHDR_FRAGMENT;
- hroom = LL_RESERVED_SPACE(rt->dst.dev);
troom = rt->dst.dev->needed_tailroom;
/*
--
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