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Date: Fri, 21 Aug 2020 14:48:01 -0400
From: Paul Moore <paul@...l-moore.com>
To: Richard Guy Briggs <rgb@...hat.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, Ondrej Mosnacek <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 V9 06/13] audit: add contid support for signalling
the audit daemon
On Wed, Jul 29, 2020 at 3:00 PM Richard Guy Briggs <rgb@...hat.com> wrote:
> On 2020-07-05 11:10, Paul Moore wrote:
> > On Sat, Jun 27, 2020 at 9:22 AM Richard Guy Briggs <rgb@...hat.com> wrote:
> > >
> > > Add audit container identifier support to the action of signalling the
> > > audit daemon.
> > >
> > > Since this would need to add an element to the audit_sig_info struct,
> > > a new record type AUDIT_SIGNAL_INFO2 was created with a new
> > > audit_sig_info2 struct. Corresponding support is required in the
> > > userspace code to reflect the new record request and reply type.
> > > An older userspace won't break since it won't know to request this
> > > record type.
> > >
> > > Signed-off-by: Richard Guy Briggs <rgb@...hat.com>
> > > ---
> > > include/linux/audit.h | 8 ++++
> > > include/uapi/linux/audit.h | 1 +
> > > kernel/audit.c | 95 ++++++++++++++++++++++++++++++++++++++++++++-
> > > security/selinux/nlmsgtab.c | 1 +
> > > 4 files changed, 104 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/include/linux/audit.h b/include/linux/audit.h
> > > index 5eeba0efffc2..89cf7c66abe6 100644
> > > --- a/include/linux/audit.h
> > > +++ b/include/linux/audit.h
> > > @@ -22,6 +22,13 @@ struct audit_sig_info {
> > > char ctx[];
> > > };
> > >
> > > +struct audit_sig_info2 {
> > > + uid_t uid;
> > > + pid_t pid;
> > > + u32 cid_len;
> > > + char data[];
> > > +};
> > > +
> > > struct audit_buffer;
> > > struct audit_context;
> > > struct inode;
> > > @@ -105,6 +112,7 @@ struct audit_contobj {
> > > u64 id;
> > > struct task_struct *owner;
> > > refcount_t refcount;
> > > + refcount_t sigflag;
> > > struct rcu_head rcu;
> > > };
> >
> > It seems like we need some protection in audit_set_contid() so that we
> > don't allow reuse of an audit container ID when "refcount == 0 &&
> > sigflag != 0", yes?
>
> We have it, see -ESHUTDOWN below.
That check in audit_set_contid() is checking ->refcount and not
->sigflag; ->sigflag is more important in this context, yes?
> > > diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
> > > index fd98460c983f..a56ad77069b9 100644
> > > --- a/include/uapi/linux/audit.h
> > > +++ b/include/uapi/linux/audit.h
> > > @@ -72,6 +72,7 @@
> > > #define AUDIT_SET_FEATURE 1018 /* Turn an audit feature on or off */
> > > #define AUDIT_GET_FEATURE 1019 /* Get which features are enabled */
> > > #define AUDIT_CONTAINER_OP 1020 /* Define the container id and info */
> > > +#define AUDIT_SIGNAL_INFO2 1021 /* Get info auditd signal sender */
> > >
> > > #define AUDIT_FIRST_USER_MSG 1100 /* Userspace messages mostly uninteresting to kernel */
> > > #define AUDIT_USER_AVC 1107 /* We filter this differently */
> > > diff --git a/kernel/audit.c b/kernel/audit.c
> > > index a09f8f661234..54dd2cb69402 100644
> > > --- a/kernel/audit.c
> > > +++ b/kernel/audit.c
> > > @@ -126,6 +126,8 @@ struct auditd_connection {
> > > kuid_t audit_sig_uid = INVALID_UID;
> > > pid_t audit_sig_pid = -1;
> > > u32 audit_sig_sid = 0;
> > > +static struct audit_contobj *audit_sig_cid;
> > > +static struct task_struct *audit_sig_atsk;
> >
> > This looks like a typo, or did you mean "atsk" for some reason?
>
> No, I meant atsk to refer specifically to the audit daemon task and not
> any other random one that is doing the signalling. I can change it is
> there is a strong objection.
Esh, yeah, "atsk" looks too much like a typo ;) At the very leask add
a 'd' in there, e.g. "adtsk", but something better than that would be
welcome.
> > > @@ -2532,6 +2620,11 @@ int audit_set_contid(struct task_struct *task, u64 contid)
> > > if (cont->id == contid) {
> > > /* task injection to existing container */
> > > if (current == cont->owner) {
> > > + if (!refcount_read(&cont->refcount)) {
> > > + rc = -ESHUTDOWN;
> >
> > Reuse -ENOTUNIQ; I'm not overly excited about providing a lot of
> > detail here as these are global system objects. If you must have a
> > different errno (and I would prefer you didn't), use something like
> > -EBUSY.
>
> I don't understand the issue of "global system objects" since the only
> time this error would be issued is if its own contid were being reused
> but it hadn't cleaned up its own references yet by either issuing an
> AUDIT_SIGNAL_INFO* request or the targetted audit daemon hadn't cleaned
> up yet. EBUSY could be confused with already having spawned threads or
> children, and ENOTUNIQ could indicate that another orchestrator/engine
> had stolen its desired contid after we released it and wanted to reuse
> it.
All the more reason for ENOTUNIQ. The point is that the audit
container ID is not available for use, and since the IDs are shared
across the entire system I think we are better off having some
ambiquity here with errnos.
> This gets me thinking about making reservations for preferred
> contids that are otherwise unavailable and making callbacks to indicate
> when they become available, but that seems undesirably complex right
> now.
That is definitely beyond the scope of this work, or rather *should*
be beyond the scope of this work.
--
paul moore
www.paul-moore.com
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