Patch "driver: vrf: Fix one possible use-after-free issue" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

driver: vrf: Fix one possible use-after-free issue

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
driver-vrf-fix-one-possible-use-after-free-issue.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Gao Feng <[email protected]>
Date: Tue, 9 May 2017 18:27:33 +0800
Subject: driver: vrf: Fix one possible use-after-free issue

From: Gao Feng <[email protected]>

[ Upstream commit 1a4a5bf52a4adb477adb075e5afce925824ad132 ]

The current codes only deal with the case that the skb is dropped, it may meet one use-after-free issue when NF_HOOK returns 0 that means the skb is stolen by one netfilter rule or hook.

When one netfilter rule or hook stoles the skb and return NF_STOLEN, it means the skb is taken by the rule, and other modules should not touch this skb ever. Maybe the skb is queued or freed directly by the rule.

Now uses the nf_hook instead of NF_HOOK to get the result of netfilter, and check the return value of nf_hook. Only when its value equals 1, it means the skb could go ahead. Or reset the skb as NULL.

BTW, because vrf_rcv_finish is empty function, so needn't invoke it even though nf_hook returns 1. But we need to modify vrf_rcv_finish to deal with the NF_STOLEN case.

There are two cases when skb is stolen.
1. The skb is stolen and freed directly.
There is nothing we need to do, and vrf_rcv_finish isn't invoked.
2. The skb is queued and reinjected again.
The vrf_rcv_finish would be invoked as okfn, so need to free the skb in it.

---
 drivers/net/vrf.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

@@ -850,6 +850,7 @@ static u32 vrf_fib_table(const struct ne
 
 static int vrf_rcv_finish(struct net *net, struct sock *sk, struct sk_buff *skb)
 {
+	kfree_skb(skb);
 	return 0;
 }
 

@@ -859,7 +860,7 @@ static struct sk_buff *vrf_rcv_nfhook(u8
 {
 	struct net *net = dev_net(dev);
 
-	if (NF_HOOK(pf, hook, net, NULL, skb, dev, NULL, vrf_rcv_finish) < 0)
+	if (nf_hook(pf, hook, net, NULL, skb, dev, NULL, vrf_rcv_finish) != 1)
 		skb = NULL;    /* kfree_skb(skb) handled by nf code */
 
 	return skb;

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/driver-vrf-fix-one-possible-use-after-free-issue.patch