Re: [PATCH 8/8] ima: Differentiate auditing policy rules from "audit" actions

[Stefan Berger]

On 05/30/2018 07:34 PM, Richard Guy Briggs wrote:
> On 2018-05-30 17:38, Stefan Berger wrote:
> > On 05/30/2018 05:22 PM, Paul Moore wrote:
> > > On Wed, May 30, 2018 at 9:08 AM, Stefan Berger
> > > <stefanb@xxxxxxxxxxxxxxxxxx> wrote:
> > > > On 05/30/2018 08:49 AM, Richard Guy Briggs wrote:
> > > > > On 2018-05-24 16:11, Stefan Berger wrote:
> > > > > > The AUDIT_INTEGRITY_RULE is used for auditing IMA policy rules and
> > > > > > the IMA "audit" policy action.  This patch defines
> > > > > > AUDIT_INTEGRITY_POLICY_RULE to reflect the IMA policy rules.
> > > > > >
> > > > > > With this change we now call integrity_audit_msg_common() to get
> > > > > > common integrity auditing fields. This now produces the following
> > > > > > record when parsing an IMA policy rule:
> > > > > >
> > > > > > type=UNKNOWN[1806] msg=audit(1527004216.690:311): action=dont_measure \
> > > > > >      fsmagic=0x9fa0 pid=1613 uid=0 auid=0 ses=2 \
> > > > > >      subj=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 \
> > > > > >      op=policy_update cause=parse_rule comm="echo" exe="/usr/bin/echo" \
> > > > > >      tty=tty2 res=1
> > > > > >
> > > > > > Signed-off-by: Stefan Berger <stefanb@xxxxxxxxxxxxxxxxxx>
> > > > > > ---
> > > > > >     include/uapi/linux/audit.h          | 3 ++-
> > > > > >     security/integrity/ima/ima_policy.c | 5 +++--
> > > > > >     2 files changed, 5 insertions(+), 3 deletions(-)
> > > > > >
> > > > > > diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
> > > > > > index 4e61a9e05132..776e0abd35cf 100644
> > > > > > --- a/include/uapi/linux/audit.h
> > > > > > +++ b/include/uapi/linux/audit.h
> > > > > > @@ -146,7 +146,8 @@
> > > > > >     #define AUDIT_INTEGRITY_STATUS            1802 /* Integrity enable
> > > > > > status */
> > > > > >     #define AUDIT_INTEGRITY_HASH      1803 /* Integrity HASH type */
> > > > > >     #define AUDIT_INTEGRITY_PCR       1804 /* PCR invalidation msgs */
> > > > > > -#define AUDIT_INTEGRITY_RULE       1805 /* policy rule */
> > > > > > +#define AUDIT_INTEGRITY_RULE       1805 /* IMA "audit" action policy
> > > > > > msgs  */
> > > > > > +#define AUDIT_INTEGRITY_POLICY_RULE 1806 /* IMA policy rules */
> > > > > >       #define AUDIT_KERNEL                2000    /* Asynchronous audit
> > > > > > record. NOT A REQUEST. */
> > > > > >     diff --git a/security/integrity/ima/ima_policy.c
> > > > > > b/security/integrity/ima/ima_policy.c
> > > > > > index 3aed25a7178a..a8ae47a386b4 100644
> > > > > > --- a/security/integrity/ima/ima_policy.c
> > > > > > +++ b/security/integrity/ima/ima_policy.c
> > > > > > @@ -634,7 +634,7 @@ static int ima_parse_rule(char *rule, struct
> > > > > > ima_rule_entry *entry)
> > > > > >           int result = 0;
> > > > > >           ab = integrity_audit_log_start(NULL, GFP_KERNEL,
> > > > > > -                                      AUDIT_INTEGRITY_RULE);
> > > > > > +                                      AUDIT_INTEGRITY_POLICY_RULE);
> > > > > Is it possible to connect this record to a syscall by replacing the
> > > > > first parameter (NULL) by current->context?
> > > We're likely going to need to "associate" this record (audit speak for
> > > making the first parameter non-NULL) with others for the audit
> > > container ID work.  If you do it now, Richard's patches will likely
> > > get a few lines smaller and that will surely make him a bit happier :)
> > Richard is also introducing a local context that we can then create and use
> > instead of the NULL. Can we not use that then?
> That is for records for which there is no syscall or user associated.
>
> In fact there is another recent change that would be better to use than
> current->audit_context, which is the function audit_context().
> See commit cdfb6b3 ("audit: use inline function to get audit context").
>
> > Steven seems to say: "We don't want to add syscall records to everything.
> > That messes up schemas and existing code. The integrity events are 1 record
> > in size and should stay that way. This saves disk space and improves
> > readability."
> >
> > > > We would have to fix current->context in this case since it is NULL. We get
> > > > to this location by root cat'ing a policy or writing a policy filename into
> > > > /sys/kernel/security/ima/policy.
> > > Perhaps I'm missing something, but current in this case should point
> > > to the process which is writing to the policy file, yes?
> > Yes, but current->context is NULL for some reason.
> Is it always this way?  If it isn't, which it should not be, we should
> find out why.  Well, we should find out why this is NULL anyways, since
> it shouldn't be.

When someone writes a policy for IMA into securityfs, it's always NULL. 
There's another location where IMA uses the current->audit_context, and 
that's here:

https://elixir.bootlin.com/linux/latest/source/security/integrity/ima/ima_api.c#L323

At this location we sometimes see a (background) process with an 
audit_context but in the majority of cases it's current->audit_context 
is NULL. Starting a process as root or also non-root user, with the 
appropriate IMA audit policy rules set, we always see a NULL 
audit_context here.


> - RGB
>
> --
> Richard Guy Briggs <rgb@xxxxxxxxxx>
> 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