On Thu, 21 Sep 2017, Dan Carpenter wrote:
> There used to be an integer overflow check in proc_do_submiturb() but
> it accidentally got removed. We need to put it back. The
The removal was deliberate, not accidental. :-)
> 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);
Sorry, I don't understand. How can division by 16384 lead to an
integer overflow?
Now, I agree that uurb->buffer_length can cause problems. We don't
check for meaningless negative values on all the execution paths (the
field should have been unsigned from the beginning). And in the
USBDEVFS_URB_TYPE_ISO case, we overwrite uurb->buffer_length without
checking that the new value is <= the old value, which could lead to a
userspace buffer overflow.
Alan Stern
> Fixes: 1129d270cbfb ("USB: Increase usbfs transfer limit")
> Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
>
> diff --git a/drivers/usb/core/devio.c b/drivers/usb/core/devio.c
> index 318bb3b96687..f3c9cff2101c 100644
> --- a/drivers/usb/core/devio.c
> +++ b/drivers/usb/core/devio.c
> @@ -140,6 +140,9 @@ 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 */
> @@ -1460,6 +1463,8 @@ 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 (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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