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                    Xen Security Advisory XSA-457
                              version 2

    Linux/xen-netfront: Memory leak due to missing cleanup function

UPDATES IN VERSION 2
====================

* Clarify the XSA is in netfront and *not* netback
* Clarify the impact: only the guest may crash

ISSUE DESCRIPTION
=================

In netfront, xennet_alloc_one_rx_buffer() failed to call the
appropriate clean-up function, resulting in a memory leak.

IMPACT
======

A malicious guest userspace process can exhaust memory resources
within the guest kernel, potentially leading to a guest crash (Denial
of Service). It is not known whether it can be triggered remotely.

VULNERABLE SYSTEMS
==================

Systems with guests running Linux 5.9 and later with Xen PV network
devices are affected.

MITIGATION
==========

For HVM guests, using emulated network devices will avoid this issue.

RESOLUTION
==========

The following patch in Linux resolves the issue:

https://git.kernel.org/torvalds/c/037965402a010898d34f4e35327d22c0a95cd51f

A copy of which is attached.

xsa457.patch           Linux 5.9

$ sha256sum xsa457*
9d6ae3da27f1ff92f9f45c800822beecda603d6dea6726207cee6c768416114c  xsa457.patch
$


NOTE ON THE LACK OF EMBARGO
===========================

The issue was reported initially on a public bug tracker and fixed in
public before it was realized that there was a security aspect.
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From 037965402a010898d34f4e35327d22c0a95cd51f Mon Sep 17 00:00:00 2001
From: Jesper Dangaard Brouer <hawk@kernel.org>
Date: Wed, 27 Mar 2024 13:14:56 +0100
Subject: xen-netfront: Add missing skb_mark_for_recycle

Notice that skb_mark_for_recycle() is introduced later than fixes tag in
commit 6a5bcd84e886 ("page_pool: Allow drivers to hint on SKB recycling").

It is believed that fixes tag were missing a call to page_pool_release_page()
between v5.9 to v5.14, after which is should have used skb_mark_for_recycle().
Since v6.6 the call page_pool_release_page() were removed (in
commit 535b9c61bdef ("net: page_pool: hide page_pool_release_page()")
and remaining callers converted (in commit 6bfef2ec0172 ("Merge branch
'net-page_pool-remove-page_pool_release_page'")).

This leak became visible in v6.8 via commit dba1b8a7ab68 ("mm/page_pool: catch
page_pool memory leaks").

Cc: stable@vger.kernel.org
Fixes: 6c5aa6fc4def ("xen networking: add basic XDP support for xen-netfront")
Reported-by: Leonidas Spyropoulos <artafinde@archlinux.com>
Link: https://bugzilla.kernel.org/show_bug.cgi?id=218654
Reported-by: Arthur Borsboom <arthurborsboom@gmail.com>
Signed-off-by: Jesper Dangaard Brouer <hawk@kernel.org>
Link: https://lore.kernel.org/r/171154167446.2671062.9127105384591237363.stgit@firesoul
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
 drivers/net/xen-netfront.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
index ad29f370034e4f..8d2aee88526c69 100644
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -285,6 +285,7 @@ static struct sk_buff *xennet_alloc_one_rx_buffer(struct netfront_queue *queue)
 		return NULL;
 	}
 	skb_add_rx_frag(skb, 0, page, 0, 0, PAGE_SIZE);
+	skb_mark_for_recycle(skb);
 
 	/* Align ip header to a 16 bytes boundary */
 	skb_reserve(skb, NET_IP_ALIGN);
-- 
cgit 1.2.3-korg