[CRIU] Re: [PATCH] proc: don't show nonexistent capabilities

[Serge E. Hallyn]

Quoting Andrew Vagin (avagin at openvz.org):
> Without this patch it is really hard to interpret a bounding set,
> if CAP_LAST_CAP is unknown for a current kernel.

To be clear, note that you *can* figure it out using
prctl(PR_CAPBSET_DROP).  But this is a nice improvement.

> 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 at canonical.com>

Thanks, Andrew.  I saw your other email about having run LTP, I didn't
see any problems from userspace either.  Great idea!

Reviewed-by: Serge Hallyn <serge.hallyn at canonical.com>

Still it's been like that for so long that, just to be safe, I'm cc:ing
Andrew Morgan - can you see any problems with this?

> Cc: Pavel Emelyanov <xemul at parallels.com>
> Signed-off-by: Andrew Vagin <avagin at openvz.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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