[PATCH] XEN: xenbus: integer overflow in process_msg()

[Haogang Chen <haogangchen@gmail.com>]

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@gmail.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