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skbuff: re-add check for NULL skb->head in kfree_skb path 

A null check is needed after all.  netlink skbs can have skb->head be
backed by vmalloc.  The netlink destructor vfree()s head, then sets it to
NULL.  We then panic in skb_release_data with a NULL dereference.

Re-add such a test.

Alternative would be to switch to kvfree to free skb->head memory
and remove the special handling in netlink destructor.

Reported-by: kernel test robot <fengguang.wu@intel.com>
Fixes: 06dc75ab06 ("net: Revert "net: add function to allocate sk_buff head without data area")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Florian Westphal 2017-07-23 19:54:47 +02:00 committed by David S. Miller
parent ba3fb10221
commit a28b1b90de
1 changed files with 2 additions and 1 deletions
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3
net/core/skbuff.c
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@ -638,7 +638,8 @@ void skb_release_head_state(struct sk_buff *skb)
static void skb_release_all(struct sk_buff *skb)
{
skb_release_head_state(skb);
skb_release_data(skb);
if (likely(skb->head))
skb_release_data(skb);
}
/**