tree b22a33022fad11706a62a926c0a462e2ea59265f
parent a6363463e8f5c7996aff6fa1285ff6c7cc3d3f6d
author Ming Lei <ming.lei@canonical.com> 1372383492 +0800
committer Greg Kroah-Hartman <gregkh@linuxfoundation.org> 1374706363 -0700

USB: check sg buffer size in usb_submit_urb

USB spec stats that short packet can only appear at the end
of transfer. Because lost of HC(EHCI/UHCI/OHCI/...) can't
build a full packet from discontinuous buffers, we introduce
the limit in usb_submit_urb() to avoid such kind of bad sg buffers
coming from driver.

The limit might be a bit strict:
	- platform has iommu to do sg list mapping
	- some host controllers may support to build full packet from
	discontinuous buffers.

But considered that most of HCs don't support that, and driver
need work well or keep consistent on different HCs and ARCHs, we
have to introduce the limit.

Currently, only usbtest is reported to pass such sg buffers to HC,
and other users(mass storage, usbfs) don't have the problem.

We don't check it on USB wireless device, because:
	- wireless devices can't be attached to common USB
	  bus(EHCI/UHCI/OHCI/...)
	- the max packet size of endpoint may be odd, and often can't
	devide 4KB which is a typical usage in usb mass storage application

Reported-by: Konstantin Filatov <kfilatov@parallels.com>
Reported-by: Denis V. Lunev <den@openvz.org>
Cc: Felipe Balbi <balbi@ti.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Ming Lei <ming.lei@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>