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commit 9180135b

 upstream.

This patch (as1262) fixes a bug in usbfs: It refuses to accept
zero-length transfers, and it insists that the buffer pointer be valid
even if there is no data being transferred.

The patch also consolidates a bunch of repetitive access_ok() checks
into a single check, which incidentally fixes the lack of such a check
for Isochronous URBs.
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>