Subject: [PATCH 5.4 04/98] netfilter: clear skb->next in NF_HOOK_LIST()

From: Greg Kroah-Hartman <[email-masked]>
Date: Tue, 1 Dec 2020 09:52:41 +0100

From: Cong Wang <[email-masked]>

NF_HOOK_LIST() uses list_del() to remove skb from the linked list,
however, it is not sufficient as skb->next still points to other
skb. We should just call skb_list_del_init() to clear skb->next,
like the rest places which using skb list.

This has been fixed in upstream by commit ca58fbe06c54
("netfilter: add and use nf_hook_slow_list()").

Fixes: 9f17dbf04ddf ("netfilter: fix use-after-free in NF_HOOK_LIST")
Reported-by: [email-masked]
Tested-by: [email-masked]
Cc: Florian Westphal <[email-masked]>
Cc: Edward Cree <[email-masked]>
Cc: [email-masked] # between 4.19 and 5.4
Signed-off-by: Cong Wang <[email-masked]>
Signed-off-by: Greg Kroah-Hartman <[email-masked]>

---
 include/linux/netfilter.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/include/linux/netfilter.h
+++ b/include/linux/netfilter.h
@@ -316,7 +316,7 @@ NF_HOOK_LIST(uint8_t pf, unsigned int ho
 
 	INIT_LIST_HEAD(&sublist);
 	list_for_each_entry_safe(skb, next, head, list) {
-		list_del(&skb->list);
+		skb_list_del_init(skb);
 		if (nf_hook(pf, hook, net, sk, skb, in, out, okfn) == 1)
 			list_add_tail(&skb->list, &sublist);
 	}