linux-kernel - Re: [PATCH] Smack: Fix wrong semantics in smk_access

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Date:   Tue, 20 Jul 2021 09:32:09 -0700
From:   Casey Schaufler <casey@...aufler-ca.com>
To:     Tianjia Zhang <tianjia.zhang@...ux.alibaba.com>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: [PATCH] Smack: Fix wrong semantics in smk_access_entry()

On 7/15/2021 8:15 AM, Casey Schaufler wrote:
> 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@...ux.alibaba.com>

Added to the Smack next branch.

>> ---
>>  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_access.c
>> index 1f391f6a3d47..d2186e2757be 100644
>> --- a/security/smack/smack_access.c
>> +++ b/security/smack/smack_access.c
>> @@ -81,23 +81,22 @@ int log_policy = SMACK_AUDIT_DENIED;
>>  int smk_access_entry(char *subject_label, char *object_label,
>>  			struct list_head *rule_list)
>>  {
>> -	int may = -ENOENT;
>>  	struct smack_rule *srp;
>>  
>>  	list_for_each_entry_rcu(srp, rule_list, list) {
>>  		if (srp->smk_object->smk_known == object_label &&
>>  		    srp->smk_subject->smk_known == subject_label) {
>> -			may = srp->smk_access;
>> -			break;
>> +			int may = srp->smk_access;
>> +			/*
>> +			 * MAY_WRITE implies MAY_LOCK.
>> +			 */
>> +			if ((may & MAY_WRITE) == MAY_WRITE)
>> +				may |= MAY_LOCK;
>> +			return may;
>>  		}
>>  	}
>>  
>> -	/*
>> -	 * MAY_WRITE implies MAY_LOCK.
>> -	 */
>> -	if ((may & MAY_WRITE) == MAY_WRITE)
>> -		may |= MAY_LOCK;
>> -	return may;
>> +	return -ENOENT;
>>  }
>>  
>>  /**