Re: [PATCH] scsi: properly count the number of pages in scsi_req_map_sg()

Dan Aloni
2006-03-21T16:18:37Z

On Tue, Mar 21, 2006 at 09:54:54AM -0600, James Bottomley wrote:
> This is a good email to discuss on the scsi list:
> linux-scsi@vger.kernel.org; whom I've added to the cc list.
>
> On Tue, 2006-03-21 at 10:38 +0200, Dan Aloni wrote:
> > Improper calculation of the number of pages causes bio_alloc() to
> > be called with nr_iovecs=0, and slab corruption later.
> >
> > For example, a simple scatterlist that fails: {(3644,452), (0, 60)},
> > (offset, size). bufflen=512 => nr_pages=1 => breakage. The proper
> > page count for this example is 2.
>
> Such a scatterlist would likely violate the device's underlying
> boundaries and is not legal ... there's supposed to be special code
> checking the queue alignment and copying the bio to an aligned buffer if
> the limits are violated. Where are you generating these scatterlists
> from?

These scatterlists can be generated using the sg driver. Though I am
actually running a customized version of the sg driver, it seems the
conversion from a userspace array of sg_iovec_t to scatterlist stays
the same and also applies to the original driver (see
st_map_user_pages()).

--
Dan Aloni
da-x@monatomic.org, da-x@colinux.org, da-x@gmx.net, dan@xiv.co.il