linux-kernel - Re: [PATCH 4/5] selinux: Enhance selinux to always ignore private inodes.

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Message-Id: <1171023977.11912.350.camel@moss-spartans.epoch.ncsc.mil>
Date:	Fri, 09 Feb 2007 07:26:17 -0500
From:	Stephen Smalley <sds@...ho.nsa.gov>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Andrew Morton <akpm@...l.org>, Ingo Molnar <mingo@...e.hu>,
	tglx@...utronix.de, linux-kernel@...r.kernel.org,
	selinux@...ho.nsa.gov, James Morris <jmorris@...ei.org>
Subject: Re: [PATCH 4/5] selinux: Enhance selinux to always ignore private
	inodes.

On Thu, 2007-02-08 at 16:02 -0700, Eric W. Biederman wrote:
> From: Stephen Smalley <sds@...ho.nsa.gov>
> 
> Hmmm...turns out to not be quite enough, as the /proc/sys inodes aren't
> truly private to the fs, so we can run into them in a variety of
> security hooks beyond just the inode hooks, such as
> security_file_permission (when reading and writing them via the vfs
> helpers), security_sb_mount (when mounting other filesystems on
> directories in proc like binfmt_misc), and deeper within the security
> module itself (as in flush_unauthorized_files upon inheritance across
> execve).  So I think we have to add an IS_PRIVATE() guard within
> SELinux, as below.  Note however that the use of the private flag here
> could be confusing, as these inodes are _not_ private to the fs, are
> exposed to userspace, and security modules must implement the sysctl
> hook to get any access control over them.

Signed-off-by:  Stephen Smalley <sds@...ho.nsa.gov>

> Signed-off-by: Eric W. Biederman <ebiederm@...ssion.com>
> 
> ---
>  security/selinux/hooks.c |    3 +++
>  1 files changed, 3 insertions(+), 0 deletions(-)
> 
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index de16b9f..ff9fccc 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -1077,6 +1077,9 @@ static int inode_has_perm(struct task_struct *tsk,
>  	struct inode_security_struct *isec;
>  	struct avc_audit_data ad;
>  
> +	if (unlikely (IS_PRIVATE (inode)))
> +		return 0;
> +
>  	tsec = tsk->security;
>  	isec = inode->i_security;
>  
-- 
Stephen Smalley
National Security Agency

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