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Subject[PATCH 3.18 24/26] USB: devio: Prevent integer overflow in proc_do_submiturb()
Date
3.18-stable review patch.  If anyone has any objections, please let me know.

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

From: Dan Carpenter <dan.carpenter@oracle.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@oracle.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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 */
@@ -1295,6 +1298,8 @@ 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 &&

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