linux-kernel - [PATCH 4.4 47/49] USB: devio: Prevent integer overflow in proc_do

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Message-Id: <20171207124710.366449646@linuxfoundation.org>
Date:   Thu,  7 Dec 2017 14:07:41 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Dan Carpenter <dan.carpenter@...cle.com>,
        Alan Stern <stern@...land.harvard.edu>
Subject: [PATCH 4.4 47/49] USB: devio: Prevent integer overflow in proc_do_submiturb()

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Dan Carpenter <dan.carpenter@...cle.com>

commit 57999d1107c1e60c2ca7088f2ac0f819e2f554b3 upstream.

There used to be an integer overflow check in proc_do_submiturb() but
we removed it.  It turns out that it's still required.  The
uurb->buffer_length variable is a signed integer and it's controlled by
the user.  It can lead to an integer overflow when we do:

	num_sgs = DIV_ROUND_UP(uurb->buffer_length, USB_SG_SIZE);

If we strip away the macro then that line looks like this:

	num_sgs = (uurb->buffer_length + USB_SG_SIZE - 1) / USB_SG_SIZE;
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
It's the first addition which can overflow.

Fixes: 1129d270cbfb ("USB: Increase usbfs transfer limit")
Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
Acked-by: Alan Stern <stern@...land.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/usb/core/devio.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/drivers/usb/core/devio.c
+++ b/drivers/usb/core/devio.c
@@ -118,6 +118,9 @@ module_param(usbfs_memory_mb, uint, 0644
 MODULE_PARM_DESC(usbfs_memory_mb,
 		"maximum MB allowed for usbfs buffers (0 = no limit)");
 
+/* Hard limit, necessary to avoid arithmetic overflow */
+#define USBFS_XFER_MAX         (UINT_MAX / 2 - 1000000)
+
 static atomic64_t usbfs_memory_usage;	/* Total memory currently allocated */
 
 /* Check whether it's okay to allocate more memory for a transfer */
@@ -1298,6 +1301,8 @@ static int proc_do_submiturb(struct usb_
 				USBDEVFS_URB_ZERO_PACKET |
 				USBDEVFS_URB_NO_INTERRUPT))
 		return -EINVAL;
+	if ((unsigned int)uurb->buffer_length >= USBFS_XFER_MAX)
+		return -EINVAL;
 	if (uurb->buffer_length > 0 && !uurb->buffer)
 		return -EINVAL;
 	if (!(uurb->type == USBDEVFS_URB_TYPE_CONTROL &&