On Wed, Jun 12, 2019 at 11:52 AM Jakub Kicinski
<jakub.kicin...@netronome.com> wrote:
>
> Brendan reports that the use of netem's packet corruption capability
> leads to strange crashes. This seems to be caused by
> commit d66280b12bd7 ("net: netem: use a list in addition to rbtree")
> which uses skb->next pointer to construct a fast-path queue of
> in-order skbs.
>
> Packet corruption code has to invoke skb_gso_segment() in case
> of skbs in need of GSO. skb_gso_segment() returns a list of
> skbs. If next pointers of the skbs on that list do not get cleared
> fast path list goes into the weeds and tries to access the next
> segment skb multiple times.
Mind to be more specific? How could it be accessed multiple times?
>
> Reported-by: Brendan Galloway <brendan.gallo...@netronome.com>
> Fixes: d66280b12bd7 ("net: netem: use a list in addition to rbtree")
> Signed-off-by: Jakub Kicinski <jakub.kicin...@netronome.com>
> Reviewed-by: Dirk van der Merwe <dirk.vanderme...@netronome.com>
> ---
> net/sched/sch_netem.c | 11 ++++-------
> 1 file changed, 4 insertions(+), 7 deletions(-)
>
> diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c
> index 956ff3da81f4..1fd4405611e5 100644
> --- a/net/sched/sch_netem.c
> +++ b/net/sched/sch_netem.c
> @@ -494,16 +494,13 @@ static int netem_enqueue(struct sk_buff *skb, struct
> Qdisc *sch,
> */
> if (q->corrupt && q->corrupt >= get_crandom(&q->corrupt_cor)) {
> if (skb_is_gso(skb)) {
> - segs = netem_segment(skb, sch, to_free);
> - if (!segs)
> + skb = netem_segment(skb, sch, to_free);
> + if (!skb)
> return rc_drop;
> - } else {
> - segs = skb;
> + segs = skb->next;
> + skb_mark_not_on_list(skb);
> }
>
> - skb = segs;
> - segs = segs->next;
> -
I don't see how this works when we hit goto finish_segs?
Either goto finish_segs can be removed or needs to be fixed?
Thanks.
