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Message-ID: <20200130175346.4ds4dursrarwv4x6@madcap2.tricolour.ca>
Date: Thu, 30 Jan 2020 12:53:46 -0500
From: Richard Guy Briggs <rgb@...hat.com>
To: Paul Moore <paul@...l-moore.com>
Cc: 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, netfilter-devel@...r.kernel.org,
sgrubb@...hat.com, omosnace@...hat.com, dhowells@...hat.com,
simo@...hat.com, Eric Paris <eparis@...isplace.org>,
Serge Hallyn <serge@...lyn.com>, ebiederm@...ssion.com,
nhorman@...driver.com, Dan Walsh <dwalsh@...hat.com>,
mpatel@...hat.com
Subject: Re: [PATCH ghak90 V8 02/16] audit: add container id
On 2020-01-22 16:28, Paul Moore wrote:
> On Tue, Dec 31, 2019 at 2:49 PM Richard Guy Briggs <rgb@...hat.com> wrote:
> >
> > Implement the proc fs write to set the audit container identifier of a
> > process, emitting an AUDIT_CONTAINER_OP record to document the event.
> >
> > This is a write from the container orchestrator task to a proc entry of
> > the form /proc/PID/audit_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).
> >
> > The writer must have capability CAP_AUDIT_CONTROL.
> >
> > This will produce a record such as this:
> > type=CONTAINER_OP msg=audit(2018-06-06 12:39:29.636:26949) : op=set opid=2209 contid=123456 old-contid=18446744073709551615
> >
> > The "op" field indicates an initial set. The "opid" field is the
> > object's PID, the process being "contained". New and old audit
> > container identifier values are given in the "contid" fields.
> >
> > It is not permitted to unset the audit container identifier.
> > A child inherits its parent's audit container identifier.
> >
> > Please see the github audit kernel issue for the main feature:
> > https://github.com/linux-audit/audit-kernel/issues/90
> > Please see the github audit userspace issue for supporting additions:
> > https://github.com/linux-audit/audit-userspace/issues/51
> > Please see the github audit testsuiite issue for the test case:
> > https://github.com/linux-audit/audit-testsuite/issues/64
> > Please see the github audit wiki for the feature overview:
> > https://github.com/linux-audit/audit-kernel/wiki/RFE-Audit-Container-ID
> >
> > Signed-off-by: Richard Guy Briggs <rgb@...hat.com>
> > Acked-by: Serge Hallyn <serge@...lyn.com>
> > Acked-by: Steve Grubb <sgrubb@...hat.com>
> > Acked-by: Neil Horman <nhorman@...driver.com>
> > Reviewed-by: Ondrej Mosnacek <omosnace@...hat.com>
> > Signed-off-by: Richard Guy Briggs <rgb@...hat.com>
> > ---
> > fs/proc/base.c | 36 ++++++++++++++++++++++++++++
> > include/linux/audit.h | 25 ++++++++++++++++++++
> > include/uapi/linux/audit.h | 2 ++
> > kernel/audit.c | 58 ++++++++++++++++++++++++++++++++++++++++++++++
> > kernel/audit.h | 1 +
> > kernel/auditsc.c | 4 ++++
> > 6 files changed, 126 insertions(+)
>
> ...
>
> > diff --git a/kernel/audit.c b/kernel/audit.c
> > index 397f8fb4836a..2d7707426b7d 100644
> > --- a/kernel/audit.c
> > +++ b/kernel/audit.c
> > @@ -2356,6 +2358,62 @@ int audit_signal_info(int sig, struct task_struct *t)
> > return audit_signal_info_syscall(t);
> > }
> >
> > +/*
> > + * audit_set_contid - set current task's audit contid
> > + * @task: target task
> > + * @contid: contid value
> > + *
> > + * Returns 0 on success, -EPERM on permission failure.
> > + *
> > + * Called (set) from fs/proc/base.c::proc_contid_write().
> > + */
> > +int audit_set_contid(struct task_struct *task, u64 contid)
> > +{
> > + u64 oldcontid;
> > + int rc = 0;
> > + struct audit_buffer *ab;
> > +
> > + task_lock(task);
> > + /* Can't set if audit disabled */
> > + if (!task->audit) {
> > + task_unlock(task);
> > + return -ENOPROTOOPT;
> > + }
> > + oldcontid = audit_get_contid(task);
> > + read_lock(&tasklist_lock);
> > + /* Don't allow the audit containerid to be unset */
> > + if (!audit_contid_valid(contid))
> > + rc = -EINVAL;
> > + /* if we don't have caps, reject */
> > + else if (!capable(CAP_AUDIT_CONTROL))
> > + rc = -EPERM;
> > + /* if task has children or is not single-threaded, deny */
> > + else if (!list_empty(&task->children))
> > + rc = -EBUSY;
> > + else if (!(thread_group_leader(task) && thread_group_empty(task)))
> > + rc = -EALREADY;
>
> [NOTE: there is a bigger issue below which I think is going to require
> a respin/fixup of this patch so I'm going to take the opportunity to
> do a bit more bikeshedding ;)]
>
> It seems like we could combine both the thread/children checks under a
> single -EBUSY return value. In both cases the caller should be able
> to determine if the target process is multi-threaded for has spawned
> children, yes? FWIW, my motivation for this question is that
> -EALREADY seems like a poor choice here.
Fair enough.
> > + /* if contid is already set, deny */
> > + else if (audit_contid_set(task))
> > + rc = -ECHILD;
>
> Does -EEXIST make more sense here?
Perhaps. I don't feel strongly about it, but none of these error codes
were intended for this use and should not overlap with other errors from
writing to /proc.
> > + read_unlock(&tasklist_lock);
> > + if (!rc)
> > + task->audit->contid = contid;
> > + task_unlock(task);
> > +
> > + if (!audit_enabled)
> > + return rc;
> > +
> > + ab = audit_log_start(audit_context(), GFP_KERNEL, AUDIT_CONTAINER_OP);
> > + if (!ab)
> > + return rc;
> > +
> > + audit_log_format(ab,
> > + "op=set opid=%d contid=%llu old-contid=%llu",
> > + task_tgid_nr(task), contid, oldcontid);
> > + audit_log_end(ab);
>
> Assuming audit is enabled we always emit the record above, even if we
> were not actually able to set the Audit Container ID (ACID); this
> seems wrong to me. I think the proper behavior would be to either add
> a "res=" field to indicate success/failure or only emit the record
> when we actually change a task's ACID. Considering the impact that
> the ACID value will potentially have on the audit stream, it seems
> like always logging the record and including a "res=" field may be the
> safer choice.
This record should be accompanied by a syscall record (and eventually
possibly a CONTAINER_ID record of the orchestrator, if it is already in
a container). The syscall record has a res= field that already gives
this result.
> > + return rc;
> > +}
> > +
> > /**
> > * audit_log_end - end one audit record
> > * @ab: the audit_buffer
>
> --
> paul moore
> www.paul-moore.com
>
- RGB
--
Richard Guy Briggs <rgb@...hat.com>
Sr. S/W Engineer, Kernel Security, Base Operating Systems
Remote, Ottawa, Red Hat Canada
IRC: rgb, SunRaycer
Voice: +1.647.777.2635, Internal: (81) 32635
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