linux-kernel - Re: [PATCH] do not export kernel's NULL #define to userspace

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Message-Id: <201203211332.06018.arnd@arndb.de>
Date:	Wed, 21 Mar 2012 13:32:05 +0000
From:	Arnd Bergmann <arnd@...db.de>
To:	Lubos Lunak <l.lunak@...e.cz>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] do not export kernel's NULL #define to userspace

On Wednesday 21 March 2012, Lubos Lunak wrote:
> GCC's NULL is actually __null, which allows detecting some questionable
> NULL usage and warn about it. Moreover each platform/compiler should have
> its own stddef.h anyway (which is different from linux/stddef.h).
> So there's no good reason to leak kernel's NULL to userspace and
> override what the compiler provides.
> 
> Signed-off-by: Luboš Luňák <l.lunak@...e.cz>

Yes, this looks like a bug, but I'm not sure that the solution is
sufficient. Have you checked the other exported header files
for whether they use NULL after including linux/stddef.h?

If so, we might have to replace it with a __KERNEL_NULL constant
or something, like we do for the stuff in linux/types.h, so we
don't accidentally break user applications that rely on the
header files to be self-contained. 

I think there is at least a NULL usage in linux/wireless.h and some
netfilter headers.

	Arnd
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