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: 06dc75ab ("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>
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