Re: kernel >= 4.0: crashes when using traceroute6 with isatap

From: Wolfgang Walter
Date: Wed May 06 2015 - 20:04:53 EST


Am Mittwoch, 6. Mai 2015, 15:42:38 schrieben Sie:
> On Thu, 2015-05-07 at 00:04 +0200, Wolfgang Walter wrote:
> > Am Mittwoch, 6. Mai 2015, 12:10:00 schrieb Eric Dumazet:
> > > On Wed, 2015-05-06 at 11:15 -0700, Cong Wang wrote:
> > > > (Cc'ing netdev.)
> > > >
> > > > On Sat, May 2, 2015 at 5:29 AM, Wolfgang Walter <linux@xxxxxxx> wrote:
> > > > > Am Samstag, 2. Mai 2015, 02:16:36 schrieb Wolfgang Walter:
> > > > >> Hello,
> > > > >>
> > > > >> kernel 4.0 (and 4.0.1) crashes immediately when I use traceroute6
> > > > >> with
> > > > >> an
> > > > >> isatap-tunnel.
> > > > >
> > > > > I did some further tests. To trigger the crash you need
> > > > >
> > > > > * isatap-tunnel (probably any sit-tunnel will do it)
> > > > > * raw-socket
> > > > > * udp
> > > > >
> > > > > Using icmpv6 or tcp i.e. does not trigger it.
> > > >
> > > > Do you have a script to reproduce it?
> > > >
> > > >
> > > > Thanks for the bug report!
> > > > --
> > >
> > > Please Wolfgang try to revert 32dce968dd987adfb0c00946d78dad9154f64759
> > > ("ipv6: Allow for partial checksums on non-ufo packets")
> >
> > Indeed, that fixes the problem.
>
> Yes, setting skb->csum to 0 is clearly wrong for CHECKSUM_PARTIAL
>
> Would you try :
>
> diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
> index
> 7fde1f265c90e90f16291e6c861b6e242111c25b..694ae630e1ca67e25ab1e5f6dd0b3597d
> b3669b0 100644 --- a/net/ipv6/ip6_output.c
> +++ b/net/ipv6/ip6_output.c
> @@ -1416,6 +1416,10 @@ alloc_new_skb:
> data += fragheaderlen;
> skb->transport_header = (skb->network_header +
> fragheaderlen);
> + if (csummode == CHECKSUM_PARTIAL) {
> + skb->csum_start = skb_transport_header(skb) - skb->head;
> + skb->csum_offset = offsetof(struct udphdr, check);
> + }
> if (fraggap) {
> skb->csum = skb_copy_and_csum_bits(
> skb_prev, maxfraglen,

This patch fixes 4.0.1 (and 4.0.2).

Thanks Eric,
--
Wolfgang Walter
Studentenwerk München
Anstalt des öffentlichen Rechts
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