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From: Paul Moore <pmoore@redhat.com>
To: Mateusz Guzik <mguzik@redhat.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>,
	Serge Hallyn <serge.hallyn@canonical.com>,
	Eric Paris <eparis@redhat.com>,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-security-module@vger.kernel.org
Subject: Re: [PATCH 1/2] CAPABILITIES: add cap_isequal helper
Date: Fri, 13 Mar 2015 10:02:46 -0400	[thread overview]
Message-ID: <7137571.s9u0Hicdri@sifl> (raw)
In-Reply-To: <1425933347-6080-2-git-send-email-mguzik@redhat.com>

On Monday, March 09, 2015 09:35:46 PM Mateusz Guzik wrote:
> Can be used to determine whether two given sets have the same
> capabilities.
> 
> Signed-off-by: Mateusz Guzik <mguzik@redhat.com>
> ---
>  include/linux/capability.h | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/include/linux/capability.h b/include/linux/capability.h
> index af9f0b9..2fcf941 100644
> --- a/include/linux/capability.h
> +++ b/include/linux/capability.h
> @@ -155,6 +155,16 @@ static inline int cap_isclear(const kernel_cap_t a)
>  	return 1;
>  }
> 
> +static inline int cap_isequal(const kernel_cap_t a, const kernel_cap_t b)
> +{
> +	unsigned __capi;
> +	CAP_FOR_EACH_U32(__capi) {
> +		if (a.cap[__capi] != b.cap[__capi])
> +			return 0;
> +	}
> +	return 1;
> +}

I realize it is currently only a two pass loop so probably not that big of a 
deal, but couldn't you accomplish the same with a memcmp()?  I suppose the 
above implementation might be faster than those architectures which use the 
generic memcmp() implementation, but I wonder if the arch-specific memcmp() 
implementations would be faster.

Also, what is the main motivation for this patchset?  Do you have a workload 
that is being hit hard by prepare_creds()?

-- 
paul moore
security @ redhat


  reply	other threads:[~2015-03-13 14:02 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-03-09 20:35 [PATCH 0/2] avoid prepare_creds in faccessat when possible Mateusz Guzik
2015-03-09 20:35 ` [PATCH 1/2] CAPABILITIES: add cap_isequal helper Mateusz Guzik
2015-03-13 14:02   ` Paul Moore [this message]
2015-03-13 16:13     ` Mateusz Guzik
2015-03-09 20:35 ` [PATCH 2/2] fs: avoid unnecessary prepare_creds in faccessat Mateusz Guzik
2015-03-13 12:08 ` [PATCH 0/2] avoid prepare_creds in faccessat when possible Mateusz Guzik

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