linux-kernel - Re: [PATCH] proc: don't show nonexistent capabilities

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Date:	Fri, 5 Oct 2012 01:42:18 +0400
From:	Andrey Wagin <avagin@...il.com>
To:	"Serge E. Hallyn" <serge@...lyn.com>
Cc:	linux-kernel@...r.kernel.org, criu@...nvz.org,
	Pavel Emelyanov <xemul@...allels.com>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	linux-security-module@...r.kernel.org
Subject: Re: [PATCH] proc: don't show nonexistent capabilities

2012/10/3 Serge E. Hallyn <serge@...lyn.com>:
> Quoting Andrew Vagin (avagin@...nvz.org):
>> Without this patch it is really hard to interpret a bounding set,
>> if CAP_LAST_CAP is unknown for a current kernel.
>>
>> Non-existant capabilities can not be deleted from a bounding set
>> with help of prctl.
>>
>> E.g.: Here are two examples without/with this patch.
>> CapBnd:       ffffffe0fdecffff
>> CapBnd:       00000000fdecffff
>>
>> I suggest to hide non-existent capabilities. Here is two reasons.
>> * It's logically and easier for using.
>> * It helps to checkpoint-restore capabilities of tasks, because tasks
>> can be restored on another kernel, where CAP_LAST_CAP is bigger.
>>
>> Cc: Serge Hallyn <serge.hallyn@...onical.com>
>
> Hm, I don't object to this patch.  Sounds useful indeed.  I can't
> help shake the feeling though that something somewhere will get
> confused by this (though it shouldn't), so I'd like to do some
> testing.  Have you run ltp against this?  Are you running this
> daily with your distro?

I've been using a kernel with this patch on my workstation (FC17) for two days.
The same kernel works on a test server (RHEL6).

I've executed LTP on the kernel with this patch and without it and the
results are not differ.
The results for both kernels are attached.

Thanks.

>
>> Cc: Pavel Emelyanov <xemul@...allels.com>
>> Signed-off-by: Andrew Vagin <avagin@...nvz.org>
>> ---
>>  include/linux/capability.h |    3 ++-
>>  1 files changed, 2 insertions(+), 1 deletions(-)
>>
>> diff --git a/include/linux/capability.h b/include/linux/capability.h
>> index d10b7ed..1642778 100644
>> --- a/include/linux/capability.h
>> +++ b/include/linux/capability.h
>> @@ -420,7 +420,8 @@ extern const kernel_cap_t __cap_init_eff_set;
>>  #else /* HAND-CODED capability initializers */
>>
>>  # define CAP_EMPTY_SET    ((kernel_cap_t){{ 0, 0 }})
>> -# define CAP_FULL_SET     ((kernel_cap_t){{ ~0, ~0 }})
>> +# define CAP_FULL_SET     ((kernel_cap_t){{ ~0, \
>> +                                     CAP_TO_MASK(CAP_LAST_CAP + 1) - 1 } })
>>  # define CAP_FS_SET       ((kernel_cap_t){{ CAP_FS_MASK_B0 \
>>                                   | CAP_TO_MASK(CAP_LINUX_IMMUTABLE), \
>>                                   CAP_FS_MASK_B1 } })
>> --
>> 1.7.1
>>
>> --
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