Re: need type to carry kernel pointers to user space

From: H. Peter Anvin (hpa@transmeta.com)
Date: Wed Jan 19 2000 - 21:21:30 EST


Followup to: <20000119130642.O42897@sfgoth.com>
By author: Mitchell Blank Jr <mitch@sfgoth.com>
In newsgroup: linux.dev.kernel
>
> Richard B. Johnson wrote:
> > > Recently, we had a discussion on the linux-atm list about the best approach
> > > for passing kernel pointers to user space, and back. The idea is as follows:
> > [SNIPPED...]
> >
> > A pointer in user space is not a pointer in kernel space! Kernel data
> > is referenced by a discriptor, referenced as KERNEL_DS, which is not
> > accessible from user-mode privilege.
>
> Yes, we (the linux-atm folks) of course know that. The pointer is
> treated as an opaque descriptor in user space, just like a file
> descriptor is passed back from open(). We just need a type
> that is garaunteed to hold a kernel-mode pointer given weird cases
> like sparc64 (suppose mips64 and hppa64 will be similar when support
> for them arrives)
>

Are you planning to dereference this pointer later? Can we say
"security hole a mile wide"?

          -hpa

-- 
<hpa@transmeta.com> at work, <hpa@zytor.com> in private!
"Unix gives you enough rope to shoot yourself in the foot."

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