LeavesHi guys,
I think code for netif_receive_skb have a bug:
int netif_receive_skb(struct sk_buff *skb)
{
struct packet_type *ptype, *pt_prev;
int ret = NET_RX_DROP;
unsigned short type = skb->protocol;
/* some code skipped */
pt_prev = NULL;
for (ptype = ptype_all; ptype; ptype = ptype->next) {
if (!ptype->dev || ptype->dev == skb->dev) {
if (pt_prev) {
if (!pt_prev->data) {
ret = deliver_to_old_ones(pt_prev,
skb, 0);
} else {
atomic_inc(&skb->users);
ret = pt_prev->func(skb, skb->dev,
pt_prev);
}
/* Would be great to add this check here */
if ( ( ret == NET_RX_DROP ) || ( ret == NET_RX_BAD ) )
{
/* Check here if skb was freed in pt_prev_>func(), if not - free it */
...
return ret;
}
}
pt_prev = ptype;
}
}
First of all, just imagine if we have only on TAP attached to ptype_all.
In this case this TAP won't be called, because of pt_prev. ( BTW, why pt_prev, why we shouldn't call the function of first chain-link? )
In second case, imagine if we have three TAPs attached to ptype_all, and second TAP desided to be an universal firewall ( third one is just ordinar TAP ). If that second TAP will call kfree_skb ( skb ), and will return the code NET_RX_DROP or NET_RX_BAD, that return code will be overwritten by third TAP, which will get freed skb, and possible panic.
The same issue for the bottom half of the function ( for ptype_base ).
what if we will add the check for it? Like I added above.
PS: BTW, how to check if skb has been freed ? I didn't found any function for it. Is it possible to add the flag, like skb->freed ?
All the Best!
Serge.
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