With a little help from Paul yesterday, I was able to come up with a
scheme for detecting bad pointers passed to system calls in linux-user
mode. This is used to return EFAULT as would be done on a real kernel.

The attached patch is very preliminary, but shows how it can be done.
I'm sending it now to solicit comments.

The patch currently just add a seperate call to validate the address. Per
yesterdays discussion, the checking should be folded into lock_user(),
but it's not a trivial drop in as lock_user() and lock_user_struct() are
used in different ways in different places, and none of them are actually
checking a return value. I'm still thinking on how best to accomplish
this part.

The end result, is that the tests in LTPs msg* tests that try to
generate EFAULT can now do so (and thus PASS).


                                 Stuart

Stuart R. Anderson                               anderson@netsweng.com
Network & Software Engineering                   http://www.netsweng.com/
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