Patch "xfrm: Fix crash observed during device unregistration and decryption" has been added to the 4.4-stable tree

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

xfrm: Fix crash observed during device unregistration and decryption

to the 4.4-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:
xfrm-fix-crash-observed-during-device-unregistration-and-decryption.patch
and it can be found in the queue-4.4 subdirectory.

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

From: "[email protected]" <[email protected]>
Date: Wed, 23 Mar 2016 22:39:50 -0600
Subject: xfrm: Fix crash observed during device unregistration and decryption

From: "[email protected]" <[email protected]>

[ Upstream commit 071d36bf21bcc837be00cea55bcef8d129e7f609 ]

A crash is observed when a decrypted packet is processed in receive path. get_rps_cpus() tries to dereference the skb->dev fields but it appears that the device is freed from the poison pattern.

[<ffffffc000af58ec>] get_rps_cpu+0x94/0x2f0
[<ffffffc000af5f94>] netif_rx_internal+0x140/0x1cc
[<ffffffc000af6094>] netif_rx+0x74/0x94
[<ffffffc000bc0b6c>] xfrm_input+0x754/0x7d0
[<ffffffc000bc0bf8>] xfrm_input_resume+0x10/0x1c
[<ffffffc000ba6eb8>] esp_input_done+0x20/0x30
[<ffffffc0000b64c8>] process_one_work+0x244/0x3fc
[<ffffffc0000b7324>] worker_thread+0x2f8/0x418
[<ffffffc0000bb40c>] kthread+0xe0/0xec

-013|get_rps_cpu(

     |    dev = 0xFFFFFFC08B688000,
     |    skb = 0xFFFFFFC0C76AAC00 -> (
     |      dev = 0xFFFFFFC08B688000 -> (
     |        name =
"......................................................
     |        name_hlist = (next = 0xAAAAAAAAAAAAAAAA, pprev =

0xAAAAAAAAAAA

Following are the sequence of events observed -

- Encrypted packet in receive path from netdevice is queued
- Encrypted packet queued for decryption (asynchronous)
- Netdevice brought down and freed
- Packet is decrypted and returned through callback in esp_input_done
- Packet is queued again for process in network stack using netif_rx

Since the device appears to have been freed, the dereference of skb->dev in get_rps_cpus() leads to an unhandled page fault exception.

Fix this by holding on to device reference when queueing packets asynchronously and releasing the reference on call back return.

v2: Make the change generic to xfrm as mentioned by Steffen and update the title to xfrm

---
 net/xfrm/xfrm_input.c |    3 +++
 1 file changed, 3 insertions(+)

@@ -292,12 +292,15 @@ int xfrm_input(struct sk_buff *skb, int
 		XFRM_SKB_CB(skb)->seq.input.hi = seq_hi;
 
 		skb_dst_force(skb);
+		dev_hold(skb->dev);
 
 		nexthdr = x->type->input(x, skb);
 
 		if (nexthdr == -EINPROGRESS)
 			return 0;
 resume:
+		dev_put(skb->dev);
+
 		spin_lock(&x->lock);
 		if (nexthdr <= 0) {
 			if (nexthdr == -EBADMSG) {

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

queue-4.4/xfrm-fix-crash-observed-during-device-unregistration-and-decryption.patch