Re: copy_from_user() fix
Richard Gooch (email@example.com)
Thu, 27 Aug 1998 07:55:28 +1000
David S. Miller writes:
> Date: Wed, 26 Aug 1998 10:55:30 +0200
> From: Martin Mares <firstname.lastname@example.org>
> To be honest, I see more legitimate advantages in SIGSEGV than
> in EFAULT. The only advantage of EFAULT is easy checking by
> callers which is IMHO used rarely. On the other hand, if you use
> SIGSEGV, you can get the faulting address and you get all accesses
> to invalid addresses trapped, making such (potentially dangerous,
> especially in security sensitive apps) cases easy to spot.
> Consider a userland pointer verification library that worked in about
> 10 lines of code by passing the pointer in question to a sys_write()
> call to /dev/null... but this wouldn't work actually these days due to
> how the kernel won't even verify the pointer in this case.
For any implementation where writing to /dev/null does nothing, this
is true. But reading from /dev/zero still has to work, which makes it
an excellent test for writability.
> But I am sure other interesting examples could be conceived.
Yeah, just fork(2)/create a thread and use a pipe.
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