Re: [PATCH] LinuxPPS (with new syscalls API)

[Robert Hancock]

David Woodhouse wrote:
> On Tue, 2007-06-26 at 19:06 +0200, Rodolfo Giometti wrote:
> > On Tue, Jun 26, 2007 at 11:57:07AM +0100, David Woodhouse wrote:
> > > Your syscalls blindly dereference userspace pointers instead of using
> > > copy_{to,from} user.
> > I use access_ok() to test userspace addresses. It should be ok,
> > shouldn't it?
>
> No; it's racy. You must use copy_from_user() and copy_to_user().

Not only is it racy, but it doesn't even do all of the checks that 
copy_to/from_user does. access_ok only validates that the region given 
is potentially valid, not that it actually is. Using access_ok only 
allows you to use __copy_to/from_user instead, which skips the same 
checks that access_ok does - not worth it unless you do repeated copies 
to/from the same region of memory.

--
Robert Hancock      Saskatoon, SK, Canada
To email, remove "nospam" from hancockr@xxxxxxxxxxxxx
Home Page: http://www.roberthancock.com/

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