[4.2.y-ckt stable] Patch "xfrm: Fix crash observed during device unregistration and decryption" has been added to the 4.2.y-ckt tree

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    xfrm: Fix crash observed during device unregistration and decryption

to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-4.2.y-queue

This patch is scheduled to be released in version 4.2.8-ckt9.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 4.2.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

---8<------------------------------------------------------------

>From 49bc029ac852300a1d401a3b4369e1eb8bca02f1 Mon Sep 17 00:00:00 2001
From: "subashab at codeaurora.org" <subashab at codeaurora.org>
Date: Wed, 23 Mar 2016 22:39:50 -0600
Subject: xfrm: Fix crash observed during device unregistration and decryption

[ 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

Suggested-by: Herbert Xu <herbert at gondor.apana.org.au>
Signed-off-by: Jerome Stanislaus <jeromes at codeaurora.org>
Signed-off-by: Subash Abhinov Kasiviswanathan <subashab at codeaurora.org>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 net/xfrm/xfrm_input.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/xfrm/xfrm_input.c b/net/xfrm/xfrm_input.c
index 60ce701..f32b959 100644
--- a/net/xfrm/xfrm_input.c
+++ b/net/xfrm/xfrm_input.c
@@ -292,12 +292,15 @@ int xfrm_input(struct sk_buff *skb, int nexthdr, __be32 spi, int encap_type)
 		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) {
--
2.7.4