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

[Kees Cook]

On Tue, Oct 2, 2012 at 10:12 PM, David Rientjes <rientjes@xxxxxxxxxx> wrote:
> 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@xxxxxxxxxxxxxx>
>> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
>
> /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.

-Kees

-- 
Kees Cook
Chrome OS Security
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