Subject: Re: [PATCH 1/6] Security: define security_sk_getsecid.

From: Casey Schaufler <[email-masked]>
Date: Tue, 09 Aug 2011 17:57:48 -0700

On 8/9/2011 5:43 PM, Rongqing Li wrote:
> On 08/10/2011 12:13 AM, Casey Schaufler wrote:
>> On 8/9/2011 12:28 AM, [email-masked] wrote:
>>> From: Roy.Li<[email-masked]>
>>>
>>> Define security_sk_getsecid to get the security id of a sock.
>>
>> Why are you requesting the secid when you're just going to
>> use it to get the secctx? Why not ask for that directly?
>> Is there ever a case where you only want the secid?
>>
> Hi:
>
> As I know, we have not method to get secctx directly.

You are defining the method! Ask for what you want!

The whole notion of secids is a holdover from the bad old
days when SELinux was a user space based enforcement mechanism.
The audit system was implemented when SELinux was the lone LSM
and unfortunately and unnecessarily propagated the use of secids.
If an object has a secid it must also have a secctx. The
interfaces that use secids could just as well use the secctx.
It is wasteful to create a new interface that fetches a secid
just to turn around and ask for the secctx in all cases.

> On the most of time, we get secctx like this.
>
> The below comes from kernel/auditsc.c
>
> void audit_log_task_context(struct audit_buffer *ab)
> {
>         char *ctx = NULL;
>         unsigned len;
>         int error;
>         u32 sid;
>
>         security_task_getsecid(current, &sid);
>         if (!sid)
>                 return;
>
>         error = security_secid_to_secctx(sid, &ctx, &len);
>         if (error) {
>                 if (error != -EINVAL)
>                         goto error_path;
>                 return;
>         }
>
>         audit_log_format(ab, " subj=%s", ctx);
>         security_release_secctx(ctx, len);
>         return;
>
> error_path:
>         audit_panic("error in audit_log_task_context");
>         return;
> }
>
>
> -Roy
>
>
>>>
>>> Signed-off-by: Roy.Li<[email-masked]>
>>> ---
>>>   include/linux/security.h |    6 ++++++
>>>   security/security.c      |    6 ++++++
>>>   2 files changed, 12 insertions(+), 0 deletions(-)
>>>
>>> diff --git a/include/linux/security.h b/include/linux/security.h
>>> index ebd2a53..739ac39 100644
>>> --- a/include/linux/security.h
>>> +++ b/include/linux/security.h
>>> @@ -2560,6 +2560,7 @@ int security_sk_alloc(struct sock *sk, int family, gfp_t priority);
>>>   void security_sk_free(struct sock *sk);
>>>   void security_sk_clone(const struct sock *sk, struct sock *newsk);
>>>   void security_sk_classify_flow(struct sock *sk, struct flowi *fl);
>>> +void security_sk_getsecid(struct sock *sk, u32 *secid);
>>>   void security_req_classify_flow(const struct request_sock *req, struct flowi *fl);
>>>   void security_sock_graft(struct sock*sk, struct socket *parent);
>>>   int security_inet_conn_request(struct sock *sk,
>>> @@ -2701,6 +2702,11 @@ static inline void security_sk_classify_flow(struct sock *sk, struct flowi *fl)
>>>   {
>>>   }
>>>
>>> +static inline void security_sk_getsecid(struct sock *sk, u32 *secid)
>>> +{
>>> +    *secid = 0;
>>> +}
>>> +
>>>   static inline void security_req_classify_flow(const struct request_sock *req, struct flowi *fl)
>>>   {
>>>   }
>>> diff --git a/security/security.c b/security/security.c
>>> index 0e4fccf..b0e0825 100644
>>> --- a/security/security.c
>>> +++ b/security/security.c
>>> @@ -1104,6 +1104,12 @@ void security_sk_classify_flow(struct sock *sk, struct flowi *fl)
>>>   }
>>>   EXPORT_SYMBOL(security_sk_classify_flow);
>>>
>>> +void security_sk_getsecid(struct sock *sk, u32 *secid)
>>> +{
>>> +    security_ops->sk_getsecid(sk, secid);
>>> +}
>>> +EXPORT_SYMBOL(security_sk_getsecid);
>>> +
>>>   void security_req_classify_flow(const struct request_sock *req, struct flowi *fl)
>>>   {
>>>       security_ops->req_classify_flow(req, fl);
>>
>>
>