netdev - [PATCH v3 net-next 2/3] netfilter: fix use-after-free in NF_HOOK

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Date:   Mon, 9 Jul 2018 18:10:02 +0100
From:   Edward Cree <ecree@...arflare.com>
To:     <davem@...emloft.net>
CC:     <netdev@...r.kernel.org>
Subject: [PATCH v3 net-next 2/3] netfilter: fix use-after-free in NF_HOOK_LIST

nf_hook() can free the skb, so we need to remove it from the list before
 calling, and add passed skbs to a sublist afterwards.

Fixes: 17266ee93984 ("net: ipv4: listified version of ip_rcv")
Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
Signed-off-by: Edward Cree <ecree@...arflare.com>
---
 include/linux/netfilter.h | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/include/linux/netfilter.h b/include/linux/netfilter.h
index 5a5e0a2ab2a3..23b48de8c2e2 100644
--- a/include/linux/netfilter.h
+++ b/include/linux/netfilter.h
@@ -294,12 +294,16 @@ NF_HOOK_LIST(uint8_t pf, unsigned int hook, struct net *net, struct sock *sk,
 	     int (*okfn)(struct net *, struct sock *, struct sk_buff *))
 {
 	struct sk_buff *skb, *next;
+	struct list_head sublist;
 
+	INIT_LIST_HEAD(&sublist);
 	list_for_each_entry_safe(skb, next, head, list) {
-		int ret = nf_hook(pf, hook, net, sk, skb, in, out, okfn);
-		if (ret != 1)
-			list_del(&skb->list);
+		list_del(&skb->list);
+		if (nf_hook(pf, hook, net, sk, skb, in, out, okfn) == 1)
+			list_add_tail(&skb->list, &sublist);
 	}
+	/* Put passed packets back on main list */
+	list_splice(&sublist, head);
 }
 
 /* Call setsockopt() */