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

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Message-ID: <0a440cef-38f0-cc11-66e6-b333b49fa82f@schaufler-ca.com>
Date:   Thu, 9 Feb 2017 08:49:53 -0800
From:   Casey Schaufler <casey@...aufler-ca.com>
To:     wharms@....de, Colin King <colin.king@...onical.com>
Cc:     James Morris <james.l.morris@...cle.com>,
        "Serge E . Hallyn" <serge@...lyn.com>,
        linux-security-module@...r.kernel.org,
        kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Smack: fix a dereference before null check on sock->sk

On 2/9/2017 5:09 AM, walter harms wrote:
>
> Am 09.02.2017 13:03, schrieb Colin King:
>> 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.
>>
>> Detected with CoverityScan, CID#1324196 ("Dereference before null check")
>>
>> Signed-off-by: Colin Ian King <colin.king@...onical.com>
>> ---
>>  security/smack/smack_lsm.c | 6 ++++--
>>  1 file changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
>> index fc8fb31..bb17387 100644
>> --- a/security/smack/smack_lsm.c
>> +++ b/security/smack/smack_lsm.c
>> @@ -2899,7 +2899,7 @@ static int smack_socket_connect(struct socket *sock, struct sockaddr *sap,
>>  #endif
>>  #ifdef SMACK_IPV6_SECMARK_LABELING
>>  	struct smack_known *rsp;
>> -	struct socket_smack *ssp = sock->sk->sk_security;
>> +	struct socket_smack *ssp;
>>  #endif
>>  
>>  	if (sock->sk == NULL)
>> @@ -2916,9 +2916,11 @@ static int smack_socket_connect(struct socket *sock, struct sockaddr *sap,
>>  			return -EINVAL;
>>  #ifdef SMACK_IPV6_SECMARK_LABELING
>>  		rsp = smack_ipv6host_label(sip);
>> -		if (rsp != NULL)
>> +		if (rsp != NULL) {
>> +			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);
>
> In the hope of reducing the ifdef forrest:
>  you could move the struct smack_known *rsp; and struct socket_smack *ssp; into the block like:
>
> {
> 	struct smack_known *rsp=smack_ipv6host_label(sip);
> 	
> 	if (rsp != NULL) {
> 		struct socket_smack *ssp= sock->sk->sk_security;
> 		rc = smk_ipv6_check(ssp->smk_out, rsp, sip,
>   						SMK_CONNECTING);
> 		}
> }
>
>
> just my 2 cents ...

I can't say that I'm proud of that chunk of code.
A real clean-up is on my todo list, and I would happily
entertain patches.

>
> re,
>  wh
>