linux-kernel - Re: [PATCH] mm: use %pK for /proc/vmallocinfo

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Date:	Tue, 2 Oct 2012 22:37:45 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Kees Cook <keescook@...omium.org>
cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Minchan Kim <minchan@...nel.org>,
	Joe Perches <joe@...ches.com>,
	Kautuk Consul <consul.kautuk@...il.com>, linux-mm@...ck.org,
	Brad Spengler <spender@...ecurity.net>
Subject: Re: [PATCH] mm: use %pK for /proc/vmallocinfo

On Tue, 2 Oct 2012, Kees Cook wrote:

> >> In the paranoid case of sysctl kernel.kptr_restrict=2, mask the kernel
> >> virtual addresses in /proc/vmallocinfo too.
> >>
> >> Reported-by: Brad Spengler <spender@...ecurity.net>
> >> Signed-off-by: Kees Cook <keescook@...omium.org>
> >
> > /proc/vmallocinfo is S_IRUSR, not S_IRUGO, so exactly what are you trying
> > to protect?
> 
> Trying to block the root user from seeing virtual memory addresses
> (mode 2 of kptr_restrict).
> 
> Documentation/sysctl/kernel.txt:
> "This toggle indicates whether restrictions are placed on
> exposing kernel addresses via /proc and other interfaces.  When
> kptr_restrict is set to (0), there are no restrictions.  When
> kptr_restrict is set to (1), the default, kernel pointers
> printed using the %pK format specifier will be replaced with 0's
> unless the user has CAP_SYSLOG.  When kptr_restrict is set to
> (2), kernel pointers printed using %pK will be replaced with 0's
> regardless of privileges."
> 
> Even though it's S_IRUSR, it still needs %pK for the paranoid case.
> 

So root does echo 0 > /proc/sys/kernel/kptr_restrict first.  Again: what 
are you trying to protect?
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