Re: [HELP] ATM: mpc, use-after-free

Eric Dumazet
2010-10-11T08:18:10Z

Le lundi 11 octobre 2010 à 09:56 +0200, Jiri Slaby a écrit :
> Hi,
>
> Stanse found this use-after-free:
>
> static void mpc_push(struct atm_vcc *vcc, struct sk_buff *skb)
> {
> ...
> new_skb = skb_realloc_headroom(skb, eg->ctrl_info.DH_length);
>
> dev_kfree_skb_any(skb);
>
> FREE ^^^^^^^^^^^^^^^^^^^^^^^
>
> if (new_skb == NULL) {
> mpc->eg_ops->put(eg);
> return;
> }
> skb_push(new_skb, eg->ctrl_info.DH_length);
> skb_copy_to_linear_data(new_skb, eg->ctrl_info.DLL_header,
> eg->ctrl_info.DH_length);
> ...
> memset(ATM_SKB(skb), 0, sizeof(struct atm_skb_data));
>
> USE ^^^^^^^^^^^^
>
> netif_rx(new_skb);
>
> I guess it should be ATM_SKB(new_skb), right?

Yes

- memset(ATM_SKB(skb), 0, sizeof(struct atm_skb_data));
+ memset(ATM_SKB(new_skb), 0, sizeof(struct atm_skb_data));

>
> The two problems are:
> 1) obvious use-after-free
> 2) ?data leak, since we don't erase the right memory?
>
> thanks,

Indeed, please submit a formal patch ?

Thanks