linux-kernel - [PATCH] XEN: xenbus: integer overflow in process

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Date:	Tue,  3 Jan 2012 14:42:11 -0500
From:	Haogang Chen <haogangchen@...il.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Ian Campbell <Ian.Campbell@...rix.com>
Cc:	xen-devel@...ts.xensource.com,
	virtualization@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, Haogang Chen <haogangchen@...il.com>
Subject: [PATCH] XEN: xenbus: integer overflow in process_msg()

There is a potential integer overflow in process_msg() that could result
in cross-domain attack.

	body = kmalloc(msg->hdr.len + 1, GFP_NOIO | __GFP_HIGH);

When a malicious guest passes 0xffffffff in msg->hdr.len, the subsequent
call to xb_read() would write to a zero-length buffer. This causes
kernel oops in the receiving guest and hangs its xenbus kernel thread.
The patch returns -EINVAL in that case.

Signed-off-by: Haogang Chen <haogangchen@...il.com>
---
 drivers/xen/xenbus/xenbus_xs.c |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/drivers/xen/xenbus/xenbus_xs.c b/drivers/xen/xenbus/xenbus_xs.c
index ede860f..e32aefb 100644
--- a/drivers/xen/xenbus/xenbus_xs.c
+++ b/drivers/xen/xenbus/xenbus_xs.c
@@ -801,6 +801,12 @@ static int process_msg(void)
 		goto out;
 	}
 
+	if (msg->hdr.len == UINT_MAX) {
+		kfree(msg);
+		err = -EINVAL;
+		goto out;
+	}
+
 	body = kmalloc(msg->hdr.len + 1, GFP_NOIO | __GFP_HIGH);
 	if (body == NULL) {
 		kfree(msg);
-- 
1.7.5.4

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