Re: [PATCH net v2] net: neigh: don't call kfree_skb() under spin_lock_irqsave()

[Yang Yingliang]

Hi,

On 2022/8/19 20:15, Nikolay Aleksandrov wrote:
> On 19/08/2022 07:47, Yang Yingliang wrote:
> > It is not allowed to call kfree_skb() from hardware interrupt
> > context or with interrupts being disabled. So add all skb to
> > a tmp list, then free them after spin_unlock_irqrestore() at
> > once.
> >
> > Fixes: 66ba215cb513 ("neigh: fix possible DoS due to net iface start/stop loop")
> > Signed-off-by: Yang Yingliang <yangyingliang@xxxxxxxxxx>
> > ---
> >   net/core/neighbour.c | 10 +++++++++-
> >   1 file changed, 9 insertions(+), 1 deletion(-)
> >
> > diff --git a/net/core/neighbour.c b/net/core/neighbour.c
> > index 5b669eb80270..d21c7de1ff1a 100644
> > --- a/net/core/neighbour.c
> > +++ b/net/core/neighbour.c
> > @@ -309,14 +309,17 @@ static int neigh_del_timer(struct neighbour *n)
> >   
> >   static void pneigh_queue_purge(struct sk_buff_head *list, struct net *net)
> >   {
> > +	struct sk_buff_head tmp;
> >   	unsigned long flags;
> >   	struct sk_buff *skb;
> >   
> > +	skb_queue_head_init(&tmp);
> >   	spin_lock_irqsave(&list->lock, flags);
> >   	skb = skb_peek(list);
> >   	while (skb != NULL) {
> >   		struct sk_buff *skb_next = skb_peek_next(skb, list);
> >   		struct net_device *dev = skb->dev;
> > +
> >   		if (net == NULL || net_eq(dev_net(dev), net)) {
> >   			struct in_device *in_dev;
> >   
> > @@ -328,11 +331,16 @@ static void :q
> (struct sk_buff_head *list, struct net *net)
> >   			__skb_unlink(skb, list);
> >   
> >   			dev_put(dev);
> > -			kfree_skb(skb);
> > +			dev_kfree_skb_irq(skb);
> this is still doing dev_kfree_skb_irq() instead of attaching the skb to tmp, in fact
> tmp seems unused so the loop below does nothing
>
> >   		}
> >   		skb = skb_next;
> >   	}
> >   	spin_unlock_irqrestore(&list->lock, flags);
> > +
> > +	while ((skb = __skb_dequeue(&tmp))) {
> > +		dev_put(skb->dev);
> Also note that there's already a dev_put() above
I made a mistake and send a wrong patch, please ignore this patch.

Thanks,
Yang
> > +		kfree_skb(skb);
> > +	}
> >   }
> >   
> >   static void neigh_flush_dev(struct neigh_table *tbl, struct net_device *dev,
>
> .