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

Casey Schaufler
2017-02-09T16:49:53Z

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@canonical.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@canonical.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
>