linux-kernel - Re: [PATCH][V2] Smack: fix a dereference before null check on sock->sk

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Message-ID: <0342e3f4-9436-ab81-fa33-a5bfe55229b7@canonical.com>
Date:   Thu, 9 Feb 2017 18:45:54 +0000
From:   Colin Ian King <colin.king@...onical.com>
To:     Casey Schaufler <casey@...aufler-ca.com>,
        James Morris <james.l.morris@...cle.com>,
        "Serge E . Hally" <serge@...lyn.com>,
        linux-security-module@...r.kernel.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][V2] Smack: fix a dereference before null check on
 sock->sk

On 09/02/17 18:44, Casey Schaufler wrote:
> On 2/9/2017 9:11 AM, Colin King wrote:
>> From: Colin Ian King <colin.king@...onical.com>
>>
>> The initialisation of pointer ssp is from a dereference on sock->sk
>> before sock-sk is null checked, hence there is a potential for a
>> null pointer deference.  Fix this by moving the assignment of ssp
>> to just before it is used in the call to smk_ipv6_check.
>>
>> Also minor clean up of code to reduce #ifdef noise.
>> Detected with CoverityScan, CID#1324196 ("Dereference before null check")
>>
>> Signed-off-by: Colin Ian King <colin.king@...onical.com>
>> ---
>>  security/smack/smack_lsm.c | 19 +++++++++++--------
>>  1 file changed, 11 insertions(+), 8 deletions(-)
>>
>> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
>> index fc8fb31..0c5656d 100644
>> --- a/security/smack/smack_lsm.c
>> +++ b/security/smack/smack_lsm.c
>> @@ -2897,10 +2897,6 @@ static int smack_socket_connect(struct socket *sock, struct sockaddr *sap,
>>  #if IS_ENABLED(CONFIG_IPV6)
>>  	struct sockaddr_in6 *sip = (struct sockaddr_in6 *)sap;
>>  #endif
>> -#ifdef SMACK_IPV6_SECMARK_LABELING
>> -	struct smack_known *rsp;
>> -	struct socket_smack *ssp = sock->sk->sk_security;
>> -#endif
>>  
>>  	if (sock->sk == NULL)
>>  		return 0;
>> @@ -2915,10 +2911,17 @@ static int smack_socket_connect(struct socket *sock, struct sockaddr *sap,
>>  		if (addrlen < sizeof(struct sockaddr_in6))
>>  			return -EINVAL;
>>  #ifdef SMACK_IPV6_SECMARK_LABELING
>> -		rsp = smack_ipv6host_label(sip);
>> -		if (rsp != NULL)
>> -			rc = smk_ipv6_check(ssp->smk_out, rsp, sip,
>> -						SMK_CONNECTING);
>> +		{
>> +			struct smack_known *rsp = smack_ipv6host_label(sip);
> 
> I make a habit of not using nested declarations.
> I appreciate the intent of the patch, but I would
> rather take a more global approach to the cleanup.

Yup. tad frustrating this, the original patch is now going to turn into
a larger change set, which was not my original intent in a trivial bug fix.

> 
>> +
>> +			if (rsp != NULL) {
>> +				struct socket_smack *ssp =
>> +					sock->sk->sk_security;
>> +
>> +				rc = smk_ipv6_check(ssp->smk_out, rsp, sip,
>> +						    SMK_CONNECTING);
>> +			}
>> +		}
>>  #endif
>>  #ifdef SMACK_IPV6_PORT_LABELING
>>  		rc = smk_ipv6_port_check(sock->sk, sip, SMK_CONNECTING);
>