Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH] Smack: Fix wrong semantics in smk_access_entry()
To:     Tianjia Zhang <tianjia.zhang@linux.alibaba.com>,
        James Morris <jmorris@namei.org>,
        "Serge E. Hallyn" <serge@hallyn.com>,
        linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20210715091724.45768-1-tianjia.zhang@linux.alibaba.com>
Cc:     Casey Schaufler <casey@schaufler-ca.com>
From:   Casey Schaufler <casey@schaufler-ca.com>
Message-ID: <ae938c7b-2f7a-27ec-7077-ceeb517ba97f@schaufler-ca.com>
Date:   Thu, 15 Jul 2021 08:15:12 -0700
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101
 Thunderbird/78.11.0
MIME-Version: 1.0
In-Reply-To: <20210715091724.45768-1-tianjia.zhang@linux.alibaba.com>
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: quoted-printable
Content-Language: en-US
Content-Length: 1583
Precedence: bulk

On 7/15/2021 2:17 AM, Tianjia Zhang wrote:
> In the smk_access_entry() function, if no matching rule is found
> in the rust_list, a negative error code will be used to perform bit
> operations with the MAY_ enumeration value. This is semantically
> wrong. This patch fixes this issue.

Indeed, the code as written is functioning correctly by
sheer luck. I will take this patch. Thank you.

>
> Signed-off-by: Tianjia Zhang <tianjia.zhang@linux.alibaba.com>
> ---
>  security/smack/smack_access.c | 17 ++++++++---------
>  1 file changed, 8 insertions(+), 9 deletions(-)
>
> diff --git a/security/smack/smack_access.c b/security/smack/smack_acces=
s.c
> index 1f391f6a3d47..d2186e2757be 100644
> --- a/security/smack/smack_access.c
> +++ b/security/smack/smack_access.c
> @@ -81,23 +81,22 @@ int log_policy =3D SMACK_AUDIT_DENIED;
>  int smk_access_entry(char *subject_label, char *object_label,
>  			struct list_head *rule_list)
>  {
> -	int may =3D -ENOENT;
>  	struct smack_rule *srp;
> =20
>  	list_for_each_entry_rcu(srp, rule_list, list) {
>  		if (srp->smk_object->smk_known =3D=3D object_label &&
>  		    srp->smk_subject->smk_known =3D=3D subject_label) {
> -			may =3D srp->smk_access;
> -			break;
> +			int may =3D srp->smk_access;
> +			/*
> +			 * MAY_WRITE implies MAY_LOCK.
> +			 */
> +			if ((may & MAY_WRITE) =3D=3D MAY_WRITE)
> +				may |=3D MAY_LOCK;
> +			return may;
>  		}
>  	}
> =20
> -	/*
> -	 * MAY_WRITE implies MAY_LOCK.
> -	 */
> -	if ((may & MAY_WRITE) =3D=3D MAY_WRITE)
> -		may |=3D MAY_LOCK;
> -	return may;
> +	return -ENOENT;
>  }
> =20
>  /**