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SubjectRe: [PATCH net v2] net: neigh: don't call kfree_skb() under spin_lock_irqsave()
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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@huawei.com>
> ---
> 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

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

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