Reported by ADLab, Venustech info Ltd CHINA:

There is a vulnerability in function clip_mkip() in net/atm/clip.c. When
re-processing received data, a struct sk_buff pointer skb may be dereferenced
after a free operation. It will lead to a kernel panic and denying further service.
 
clip_mkip (clip.c):

502         while ((skb = skb_dequeue(&copy)) != NULL)
503                 if (!clip_devs) {
504                         atm_return(vcc,skb->truesize);
505                         kfree_skb(skb);
506                 }
507                 else {
508                         unsigned int len = skb->len;
509
510                         clip_push(vcc,skb);
511                         PRIV(skb->dev)->stats.rx_packets--;
512                         PRIV(skb->dev)->stats.rx_bytes -= len;
513                 }
 
At line 511, PRIV(skb->dev) reference skb->dev; but after call clip_push at line
510, skb may be freed.
 
clip_push (clip.c):

198 static void clip_push(struct atm_vcc *vcc,struct sk_buff *skb)
199 {

	......

234         memset(ATM_SKB(skb), 0, sizeof(struct atm_skb_data));
235         netif_rx(skb);
236 }
 
netif_rx (dev.c):

1392 int netif_rx(struct sk_buff *skb)
1393 {

	......

1428         kfree_skb(skb);	//drop skb
1429         return NET_RX_DROP;
1430 }

In netif_rx(), skb may be dropped during processing for congestion control or by
the protocol layers; the return value NET_RX_DROP is used to identify skb
pointer arg is dropped(freed).