linux-kernel - Re: [RFC 4/8] lsm: smack: smack callbacks for kdbus security hooks

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Message-ID: <559D28DE.4070406@tycho.nsa.gov>
Date:	Wed, 08 Jul 2015 09:42:54 -0400
From:	Stephen Smalley <sds@...ho.nsa.gov>
To:	Paul Osmialowski <p.osmialowsk@...sung.com>,
	Paul Moore <pmoore@...hat.com>,
	James Morris <james.l.morris@...cle.com>,
	Casey Schaufler <casey@...aufler-ca.com>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	Kees Cook <keescook@...omium.org>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	Neil Brown <neilb@...e.de>,
	Mark Rustad <mark.d.rustad@...el.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Daniel Mack <daniel@...que.org>,
	David Herrmann <dh.herrmann@...glemail.com>,
	Djalal Harouni <tixxdz@...ndz.org>,
	Shuah Khan <shuahkh@....samsung.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	linux-security-module@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-api@...r.kernel.org
CC:	Karol Lewandowski <k.lewandowsk@...sung.com>,
	Lukasz Skalski <l.skalski@...sung.com>
Subject: Re: [RFC 4/8] lsm: smack: smack callbacks for kdbus security hooks

On 07/08/2015 06:25 AM, Paul Osmialowski wrote:
> This adds implementation of three smack callbacks sitting behind kdbus
> security hooks as proposed by Karol Lewandowski.
> 
> Originates from:
> 
> git://git.infradead.org/users/pcmoore/selinux (branch: working-kdbus)
> commit: fc3505d058c001fe72a6f66b833e0be5b2d118f3
> 
> https://github.com/lmctl/linux.git (branch: kdbus-lsm-v4.for-systemd-v212)
> commit: 103c26fd27d1ec8c32d85dd3d85681f936ac66fb
> 
> Signed-off-by: Karol Lewandowski <k.lewandowsk@...sung.com>
> Signed-off-by: Paul Osmialowski <p.osmialowsk@...sung.com>
> ---
>  security/smack/smack_lsm.c | 68 ++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 68 insertions(+)
> 
> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
> index a143328..033b756 100644
> --- a/security/smack/smack_lsm.c
> +++ b/security/smack/smack_lsm.c
> @@ -41,6 +41,7 @@
>  #include <linux/msg.h>
>  #include <linux/shm.h>
>  #include <linux/binfmts.h>
> +#include <kdbus/connection.h>
>  #include "smack.h"
>  
>  #define TRANS_TRUE	"TRUE"
> @@ -3336,6 +3337,69 @@ static int smack_setprocattr(struct task_struct *p, char *name,
>  }
>  
>  /**
> + * smack_kdbus_connect - Set the security blob for a KDBus connection
> + * @conn: the connection
> + * @secctx: smack label
> + * @seclen: smack label length
> + *
> + * Returns 0
> + */
> +static int smack_kdbus_connect(struct kdbus_conn *conn,
> +			       const char *secctx, u32 seclen)
> +{
> +	struct smack_known *skp;
> +
> +	if (secctx && seclen > 0)
> +		skp = smk_import_entry(secctx, seclen);
> +	else
> +		skp = smk_of_current();
> +	conn->security = skp;
> +
> +	return 0;
> +}
> +
> +/**
> + * smack_kdbus_conn_free - Clear the security blob for a KDBus connection
> + * @conn: the connection
> + *
> + * Clears the blob pointer
> + */
> +static void smack_kdbus_conn_free(struct kdbus_conn *conn)
> +{
> +	conn->security = NULL;
> +}
> +
> +/**
> + * smack_kdbus_talk - Smack access on KDBus
> + * @src: source kdbus connection
> + * @dst: destination kdbus connection
> + *
> + * Return 0 if a subject with the smack of sock could access
> + * an object with the smack of other, otherwise an error code
> + */
> +static int smack_kdbus_talk(const struct kdbus_conn *src,
> +			    const struct kdbus_conn *dst)
> +{
> +	struct smk_audit_info ad;
> +	struct smack_known *sskp = src->security;
> +	struct smack_known *dskp = dst->security;
> +	int ret;
> +
> +	BUG_ON(sskp == NULL);
> +	BUG_ON(dskp == NULL);
> +
> +	if (smack_privileged(CAP_MAC_OVERRIDE))
> +		return 0;
> +
> +	smk_ad_init(&ad, __func__, LSM_AUDIT_DATA_NONE);
> +
> +	ret = smk_access(sskp, dskp, MAY_WRITE, &ad);
> +	if (ret)
> +		return ret;
> +	return 0;
> +}
> +
> +/**
>   * smack_unix_stream_connect - Smack access on UDS
>   * @sock: one sock
>   * @other: the other sock
> @@ -4393,6 +4457,10 @@ struct security_hook_list smack_hooks[] = {
>  	LSM_HOOK_INIT(inode_notifysecctx, smack_inode_notifysecctx),
>  	LSM_HOOK_INIT(inode_setsecctx, smack_inode_setsecctx),
>  	LSM_HOOK_INIT(inode_getsecctx, smack_inode_getsecctx),
> +
> +	LSM_HOOK_INIT(kdbus_connect, smack_kdbus_connect),
> +	LSM_HOOK_INIT(kdbus_conn_free, smack_kdbus_conn_free),
> +	LSM_HOOK_INIT(kdbus_talk, smack_kdbus_talk),
>  };

If Smack only truly needs 3 hooks, then it begs the question of why
there are so many other hooks defined.  Are the other hooks just to
support finer-grained distinctions, or is Smack's coverage incomplete?

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