linux-kernel - Re: [PATCH] devcgroup: fix odd behaviour when writing 'a' to devices.allow

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Date:	Mon, 7 Jul 2008 12:25:46 -0500
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	Li Zefan <lizf@...fujitsu.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] devcgroup: fix odd behaviour when writing 'a' to
	devices.allow

Quoting Li Zefan (lizf@...fujitsu.com):
>  # cat /devcg/devices.list
>  a *:* rwm
>  # echo a > devices.allow
>  # cat /devcg/devices.list
>  a *:* rwm
>  a 0:0 rwm
> 
> This is odd and maybe confusing. With this patch, writing 'a'
> to devices.allow will add 'a *:* rwm' to the whitelist.
> 
> Also a few fixes and updates to the document.
> 
> Signed-off-by: Li Zefan <lizf@...fujitsu.com>

Acked-by: Serge Hallyn <serue@...ibm.com>

thanks,
-serge

> ---
>  Documentation/controllers/devices.txt |    8 ++++++--
>  security/device_cgroup.c              |    2 ++
>  2 files changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/controllers/devices.txt b/Documentation/controllers/devices.txt
> index 4dcea42..7cc6e6a 100644
> --- a/Documentation/controllers/devices.txt
> +++ b/Documentation/controllers/devices.txt
> @@ -13,7 +13,7 @@ either an integer or * for all.  Access is a composition of r
>  The root device cgroup starts with rwm to 'all'.  A child device
>  cgroup gets a copy of the parent.  Administrators can then remove
>  devices from the whitelist or add new entries.  A child cgroup can
> -never receive a device access which is denied its parent.  However
> +never receive a device access which is denied by its parent.  However
>  when a device access is removed from a parent it will not also be
>  removed from the child(ren).
> 
> @@ -29,7 +29,11 @@ allows cgroup 1 to read and mknod the device usually known as
> 
>  	echo a > /cgroups/1/devices.deny
> 
> -will remove the default 'a *:* mrw' entry.
> +will remove the default 'a *:* rwm' entry. Doing
> +
> +	echo a > /cgroups/1/devices.allow
> +
> +will add the 'a *:* rwm' entry to the whitelist.
> 
>  3. Security
> 
> diff --git a/security/device_cgroup.c b/security/device_cgroup.c
> index baf3488..fd764a0 100644
> --- a/security/device_cgroup.c
> +++ b/security/device_cgroup.c
> @@ -382,6 +382,8 @@ static ssize_t devcgroup_access_write(struct cgroup *cgroup, struct cftype *cft,
>  	case 'a':
>  		wh.type = DEV_ALL;
>  		wh.access = ACC_MASK;
> +		wh.major = ~0;
> +		wh.minor = ~0;
>  		goto handle;
>  	case 'b':
>  		wh.type = DEV_BLOCK;
> -- 
> 1.5.4.rc3
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