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net: skb_condense() can also deal with empty skbs 

It seems attackers can also send UDP packets with no payload at all.

skb_condense() can still be a win in this case.

It will be possible to replace the custom code in tcp_add_backlog()
to get full benefit from skb_condense()

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2016-12-09 08:02:05 -08:00 committed by David S. Miller
parent 5ac9efbe1c
commit 3174fed982
1 changed files with 13 additions and 9 deletions
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22
net/core/skbuff.c
View File

@ -4946,16 +4946,20 @@ EXPORT_SYMBOL(pskb_extract);
*/
void skb_condense(struct sk_buff *skb)
{
if (!skb->data_len ||
skb->data_len > skb->end - skb->tail ||
skb_cloned(skb))
return;
if (skb->data_len) {
if (skb->data_len > skb->end - skb->tail ||
skb_cloned(skb))
return;
/* Nice, we can free page frag(s) right now */
__pskb_pull_tail(skb, skb->data_len);
/* Now adjust skb->truesize, since __pskb_pull_tail() does
* not do this.
/* Nice, we can free page frag(s) right now */
__pskb_pull_tail(skb, skb->data_len);
}
/* At this point, skb->truesize might be over estimated,
* because skb had a fragment, and fragments do not tell
* their truesize.
* When we pulled its content into skb->head, fragment
* was freed, but __pskb_pull_tail() could not possibly
* adjust skb->truesize, not knowing the frag truesize.
*/
skb->truesize = SKB_TRUESIZE(skb_end_offset(skb));
}