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
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Home Page: http://www.roberthancock.com/
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