Subject: Re: [PATCH net-next] bpf: fix the printing of ifindex

From: Daniel Borkmann <[email-masked]>
Date: Wed, 02 Aug 2017 17:53:45 +0200

On 08/02/2017 05:43 PM, William Tu wrote:
> Save the ifindex before it gets zeroed so the invalid
> ifindex can be printed out.
>
> Signed-off-by: William Tu <[email-masked]>

Acked-by: Daniel Borkmann <[email-masked]>

>   net/core/filter.c | 10 ++++++----
>   1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 7e9708653c6f..78d00933dbe7 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -2509,15 +2509,16 @@ int xdp_do_redirect(struct net_device *dev, struct xdp_buff *xdp,
>   {
>   	struct redirect_info *ri = this_cpu_ptr(&redirect_info);
>   	struct net_device *fwd;
> +	u32 index = ri->ifindex;
>
>   	if (ri->map)
>   		return xdp_do_redirect_map(dev, xdp, xdp_prog);
>
> -	fwd = dev_get_by_index_rcu(dev_net(dev), ri->ifindex);
> +	fwd = dev_get_by_index_rcu(dev_net(dev), index);
>   	ri->ifindex = 0;
>   	ri->map = NULL;

Unrelated, but setting ri->map to NULL is not really needed here
given we have the ri->map test earlier.

>   	if (unlikely(!fwd)) {
> -		bpf_warn_invalid_xdp_redirect(ri->ifindex);
> +		bpf_warn_invalid_xdp_redirect(index);
>   		return -EINVAL;
>   	}
>
> @@ -2531,11 +2532,12 @@ int xdp_do_generic_redirect(struct net_device *dev, struct sk_buff *skb)
>   {
>   	struct redirect_info *ri = this_cpu_ptr(&redirect_info);
>   	unsigned int len;
> +	u32 index = ri->ifindex;
>
> -	dev = dev_get_by_index_rcu(dev_net(dev), ri->ifindex);
> +	dev = dev_get_by_index_rcu(dev_net(dev), index);
>   	ri->ifindex = 0;
>   	if (unlikely(!dev)) {
> -		bpf_warn_invalid_xdp_redirect(ri->ifindex);
> +		bpf_warn_invalid_xdp_redirect(index);
>   		goto err;
>   	}
>
>