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SubjectRe: [PATCH] xfrm : lock input tasklet skb queue
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Hi,

I already send a patch on 2019-09-09 to this mailing list with a similar
issue[1].
Sadly no replies, although this is a huge bug in the rt kernel.
I fixed it a bit differently, using smaller locked regions.
You have also propably a bug in your patch, because trans->queue.lock is
no initialized by __skb_queue_head_init (in xfrm_input_init)

Jörg

[1] https://lkml.org/lkml/2019/9/9/111

Am 20.10.2019 um 17:46 schrieb Tom Rix:
> On PREEMPT_RT_FULL while running netperf, a corruption
> of the skb queue causes an oops.
>
> This appears to be caused by a race condition here
> __skb_queue_tail(&trans->queue, skb);
> tasklet_schedule(&trans->tasklet);
> Where the queue is changed before the tasklet is locked by
> tasklet_schedule.
>
> The fix is to use the skb queue lock.
>
> Signed-off-by: Tom Rix <trix@redhat.com>
> ---
> net/xfrm/xfrm_input.c | 11 ++++++++++-
> 1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/net/xfrm/xfrm_input.c b/net/xfrm/xfrm_input.c
> index 9b599ed66d97..226dead86828 100644
> --- a/net/xfrm/xfrm_input.c
> +++ b/net/xfrm/xfrm_input.c
> @@ -758,12 +758,16 @@ static void xfrm_trans_reinject(unsigned long data)
> struct xfrm_trans_tasklet *trans = (void *)data;
> struct sk_buff_head queue;
> struct sk_buff *skb;
> + unsigned long flags;
>
> __skb_queue_head_init(&queue);
> + spin_lock_irqsave(&trans->queue.lock, flags);
> skb_queue_splice_init(&trans->queue, &queue);
>
> while ((skb = __skb_dequeue(&queue)))
> XFRM_TRANS_SKB_CB(skb)->finish(dev_net(skb->dev), NULL, skb);
> +
> + spin_unlock_irqrestore(&trans->queue.lock, flags);
> }
>
> int xfrm_trans_queue(struct sk_buff *skb,
> @@ -771,15 +775,20 @@ int xfrm_trans_queue(struct sk_buff *skb,
> struct sk_buff *))
> {
> struct xfrm_trans_tasklet *trans;
> + unsigned long flags;
>
> trans = this_cpu_ptr(&xfrm_trans_tasklet);
> + spin_lock_irqsave(&trans->queue.lock, flags);
>
> - if (skb_queue_len(&trans->queue) >= netdev_max_backlog)
> + if (skb_queue_len(&trans->queue) >= netdev_max_backlog) {
> + spin_unlock_irqrestore(&trans->queue.lock, flags);
> return -ENOBUFS;
> + }
>
> XFRM_TRANS_SKB_CB(skb)->finish = finish;
> __skb_queue_tail(&trans->queue, skb);
> tasklet_schedule(&trans->tasklet);
> + spin_unlock_irqrestore(&trans->queue.lock, flags);
> return 0;
> }
> EXPORT_SYMBOL(xfrm_trans_queue);

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