linux-kernel - Re: [RFC PATCH V1 01/12] audit: add container id

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Date:   Thu, 15 Mar 2018 16:27:01 -0400
From:   Stefan Berger <stefanb@...ux.vnet.ibm.com>
To:     Richard Guy Briggs <rgb@...hat.com>, cgroups@...r.kernel.org,
        containers@...ts.linux-foundation.org, linux-api@...r.kernel.org,
        Linux-Audit Mailing List <linux-audit@...hat.com>,
        linux-fsdevel@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        netdev@...r.kernel.org
Cc:     mszeredi@...hat.com, luto@...nel.org, jlayton@...hat.com,
        carlos@...hat.com, viro@...iv.linux.org.uk, dhowells@...hat.com,
        simo@...hat.com, trondmy@...marydata.com, eparis@...isplace.org,
        serge@...lyn.com, ebiederm@...ssion.com, madzcar@...il.com
Subject: Re: [RFC PATCH V1 01/12] audit: add container id

On 03/01/2018 02:41 PM, Richard Guy Briggs wrote:
> Implement the proc fs write to set the audit container ID of a process,
> emitting an AUDIT_CONTAINER record to document the event.
>
> This is a write from the container orchestrator task to a proc entry of
> the form /proc/PID/containerid where PID is the process ID of the newly
> created task that is to become the first task in a container, or an
> additional task added to a container.
>
> The write expects up to a u64 value (unset: 18446744073709551615).
>
> This will produce a record such as this:
> type=UNKNOWN[1333] msg=audit(1519903238.968:261): op=set pid=596 uid=0 subj=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 auid=0 tty=pts0 ses=1 opid=596 old-contid=18446744073709551615 contid=123455 res=0
>
> The "op" field indicates an initial set.  The "pid" to "ses" fields are
> the orchestrator while the "opid" field is the object's PID, the process
> being "contained".  Old and new container ID values are given in the
> "contid" fields, while res indicates its success.
>
> It is not permitted to self-set, unset or re-set the container ID.  A
> child inherits its parent's container ID, but then can be set only once
> after.
>
> See: https://github.com/linux-audit/audit-kernel/issues/32
>
>
>   /* audit_rule_data supports filter rules with both integer and string
>    * fields.  It corresponds with AUDIT_ADD_RULE, AUDIT_DEL_RULE and
> diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> index 4e0a4ac..0ee1e59 100644
> --- a/kernel/auditsc.c
> +++ b/kernel/auditsc.c
> @@ -2073,6 +2073,92 @@ int audit_set_loginuid(kuid_t loginuid)
>   	return rc;
>   }
>
> +static int audit_set_containerid_perm(struct task_struct *task, u64 containerid)
> +{
> +	struct task_struct *parent;
> +	u64 pcontainerid, ccontainerid;
> +	pid_t ppid;
> +
> +	/* Don't allow to set our own containerid */
> +	if (current == task)
> +		return -EPERM;
> +	/* Don't allow the containerid to be unset */
> +	if (!cid_valid(containerid))
> +		return -EINVAL;
> +	/* if we don't have caps, reject */
> +	if (!capable(CAP_AUDIT_CONTROL))
> +		return -EPERM;
> +	/* if containerid is unset, allow */
> +	if (!audit_containerid_set(task))
> +		return 0;

I am wondering whether there should be a check for the target process 
that will receive the containerid to not have CAP_SYS_ADMIN that would 
otherwise allow it to arbitrarily unshare()/clone() and leave the set of 
namespaces that may make up the container whose containerid we assign here?

> +	/* it is already set, and not inherited from the parent, reject */
> +	ccontainerid = audit_get_containerid(task);
> +	rcu_read_lock();
> +	parent = rcu_dereference(task->real_parent);
> +	rcu_read_unlock();
> +	task_lock(parent);
> +	pcontainerid = audit_get_containerid(parent);
> +	ppid = task_tgid_nr(parent);
ppid not needed...

> +	task_unlock(parent);
> +	if (ccontainerid != pcontainerid)
> +		return -EPERM;
> +	return 0;
> +}
> +
> +static void audit_log_set_containerid(struct task_struct *task, u64 oldcontainerid,
> +				      u64 containerid, int rc)
> +{
> +	struct audit_buffer *ab;
> +	uid_t uid;
> +	struct tty_struct *tty;
> +
> +	if (!audit_enabled)
> +		return;
> +
> +	ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_CONTAINER);
> +	if (!ab)
> +		return;
> +
> +	uid = from_kuid(&init_user_ns, task_uid(current));
> +	tty = audit_get_tty(current);
> +
> +	audit_log_format(ab, "op=set pid=%d uid=%u", task_tgid_nr(current), uid);
> +	audit_log_task_context(ab);
> +	audit_log_format(ab, " auid=%u tty=%s ses=%u opid=%d old-contid=%llu contid=%llu res=%d",
> +			 from_kuid(&init_user_ns, audit_get_loginuid(current)),
> +			 tty ? tty_name(tty) : "(none)", audit_get_sessionid(current),
> +			 task_tgid_nr(task), oldcontainerid, containerid, !rc);
> +
> +	audit_put_tty(tty);
> +	audit_log_end(ab);
> +}
> +
> +/**
> + * audit_set_containerid - set current task's audit_context containerid
> + * @containerid: containerid value
> + *
> + * Returns 0 on success, -EPERM on permission failure.
> + *
> + * Called (set) from fs/proc/base.c::proc_containerid_write().
> + */
> +int audit_set_containerid(struct task_struct *task, u64 containerid)
> +{
> +	u64 oldcontainerid;
> +	int rc;
> +
> +	oldcontainerid = audit_get_containerid(task);
> +
> +	rc = audit_set_containerid_perm(task, containerid);
> +	if (!rc) {
> +		task_lock(task);
> +		task->containerid = containerid;
> +		task_unlock(task);
> +	}
> +
> +	audit_log_set_containerid(task, oldcontainerid, containerid, rc);
> +	return rc;
> +}
> +
>   /**
>    * __audit_mq_open - record audit data for a POSIX MQ open
>    * @oflag: open flag