linux-kernel - Re: Patch [1/1] minor bugfix in 2.6.26/arch/x86/mm/pat.c - caused problems in mmap() of /dev/mem character file

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Date:	Thu, 17 Jul 2008 10:27:03 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	"V.Radhakrishnan" <rk@...-labs.com>, Ingo Molnar <mingo@...e.hu>
cc:	Linux Kernel Mailing List <Linux-kernel@...r.kernel.org>
Subject: Re: Patch [1/1] minor bugfix in 2.6.26/arch/x86/mm/pat.c - caused
 problems in mmap() of /dev/mem character file



On Thu, 17 Jul 2008, V.Radhakrishnan wrote:
> 
> The above #ifdef must be actually #ifndef and not #ifdef
> The bug does not allow a valid user (root) from accessing /dev/mem even
> though the CONFIG_PROMISC_DEVMEM is NOT selected.

The real bug is that we shouldn't have "double negatives", and certainly 
not negative config options. Making that "promiscuous /dev/mem" option a 
negated thing as a config option was bad.

Ingo, over to you..

		Linus

> --- arch/x86/mm/pat.c.orig	2008-07-17 22:04:18.000000000 +0530
> +++ arch/x86/mm/pat.c	2008-07-17 22:43:39.000000000 +0530
> @@ -471,7 +475,7 @@ pgprot_t phys_mem_access_prot(struct fil
>  	return vma_prot;
>  }
>  
> -#ifdef CONFIG_NONPROMISC_DEVMEM
> +#ifndef CONFIG_NONPROMISC_DEVMEM
>  /* This check is done in drivers/char/mem.c in case of NONPROMISC_DEVMEM*/
>  static inline int range_is_allowed(unsigned long pfn, unsigned long size)
>  {
> @@ -586,4 +590,3 @@ void unmap_devmem(unsigned long pfn, uns
--
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