[added to the 4.1 stable tree] USB: devio: Prevent integer overflow in proc_do_submiturb()

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From: Dan Carpenter <dan.carpenter@xxxxxxxxxx>

This patch has been added to the  stable tree. If you have any
objections, please let us know.

===============

[ Upstream commit 57999d1107c1e60c2ca7088f2ac0f819e2f554b3 ]

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")
Cc: stable <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Acked-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
---
 drivers/usb/core/devio.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/usb/core/devio.c b/drivers/usb/core/devio.c
index de9fa65bb03b..25e0cfe0d407 100644
--- 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_dev_state *ps, struct usbdevfs_urb *uurb
 				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 &&
-- 
2.11.0




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