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

Jiri Slaby
2010-10-11T07:56:44Z

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?

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

thanks,
--
js