Re: [PATCH] audit: add containerid support for IMA-audit

[Stefan Berger]

On 03/08/2018 06:21 AM, Richard Guy Briggs wrote:
> On 2018-03-05 09:24, Mimi Zohar wrote:
> > On Mon, 2018-03-05 at 08:50 -0500, Richard Guy Briggs wrote:
> > > On 2018-03-05 08:43, Mimi Zohar wrote:
> > > > Hi Richard,
> > > >
> > > > This patch has been compiled, but not runtime tested.
> > > Ok, great, thank you.  I assume you are offering this patch to be
> > > included in this patchset?
> > Yes, thank you.
> >
> > > I'll have a look to see where it fits in the
> > > IMA record.  It might be better if it were an AUDIT_CONTAINER_INFO
> > > auxiliary record, but I'll have a look at the circumstances of the
> > > event.
> I had a look at the context of this record to see if adding the contid
> field to it made sense.  I think the only records for which the contid
> field makes sense are the two newly proposed records, AUDIT_CONTAINER
> which introduces the container ID and the and AUDIT_CONTAINER_INFO which
> documents the presence of the container ID in a process event (or
> process-less network event).  All others should use the auxiliary record
> AUDIT_CONTAINER_INFO rather than include the contid field directly
> itself.  There are several reasons for this including record length, the
> ability to filter unwanted records, the difficulty of changing the order
> of or removing fields in the future.
>
> Syscalls get this information automatically if the container ID is set
> for a task via the AUDIT_CONTAINER_INFO auxiliary record.  Generally a
> syscall event is one that uses the task's audit_context while a
> standalone event uses NULL or builds a local audit_context that is
> discarded immediately after the local use.
>
> Looking at the two cases of AUDIT_INTEGRITY_RULE record generation, it
> appears that they should be split into two distinct audit record types.
>
> The record created in ima_audit_measurement() is a syscall record that
> could possibly stand on its own since the subject attributes are
> present.  If it remains a syscall auxiliary record it will automatically
> have the AUDIT_CONTAINER_INFO record accompany it anyways.  If it is
> decided to detach it (which would save cpu/netlink/disk bandwidth but is
> not recommended due to not wanting to throw away any other syscall
> information or other involved records (PATH, CWD, etc...) then a local
> audit_context would be created for the AUDIT_INTEGRITY_RULE and
> AUDIT_CONTAINERID_INFO records only and immediately discarded.

What does 'detach it' mean? Does it mean we're not using 
current->audit_context?

> The record created in ima_parse_rule() is not currently a syscall record
> since it is passed an audit_context of NULL and it has a very different
> format that does not include any subject attributes (except subj_*=).
> At first glance it appears this one should be a syscall accompanied
> auxiliary record.  Either way it should have an AUDIT_CONTAINER_INFO

Do you have an example (pointer) to the format for a 'syscall 
accompanied auxiliary record'?

> auxiliary record either by being converted to a syscall auxiliary record
> by using current->audit_context rather than NULL when calling
> audit_log_start(), or creating a local audit_context and calling

ima_parse_rule() is invoked when setting a policy by writing it into 
/sys/kernel/security/ima/policy. We unfortunately don't have the 
current->audit_context in this case.

> audit_log_container_info() then releasing the local context.  This
> version of the record has additional concerns covered here:
> https://github.com/linux-audit/audit-kernel/issues/52

Following the discussion there and the concern with breaking user space, 
how can we split up the AUDIT_INTEGRITY_RULE that is used in 
ima_audit_measurement() and ima_parse_rule(), without 'breaking user space'?

A message produced by ima_parse_rule() looks like this here:

type=INTEGRITY_RULE msg=audit(1526566213.870:305): action="dont_measure" 
fsmagic="0x9fa0" res=1

in contrast to that an INTEGRITY_PCR record type:

type=INTEGRITY_PCR msg=audit(1526566235.193:334): pid=1615 uid=0 auid=0 
ses=2 subj=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 
op="invalid_pcr" cause="open_writers" comm="scp" 
name="/var/log/audit/audit.log" dev="dm-0" ino=1962625 res=1

Should some of the fields from INTEGRITY_PCR also appear in 
INTEGRITY_RULE? If so, which ones? We could probably refactor the 
current integrity_audit_message() and have ima_parse_rule() call into 
it to get those fields as well. I suppose adding new fields to it 
wouldn't be considered breaking user space?

ÂÂÂ Stefan


> Can you briefly describe the circumstances under which these two
> different identically-numbered records are produced as a first step
> towards splitting them into two distict records?
>
> The four AUDIT_INTEGRITY _METADATA, _PCR, _DATA and _STATUS records
> appear to be already properly covered for AUDIT_CONTAINER_INFO records
> by being syscall auxiliary records.  The AUDIT_INTEGRITY_HASH record
> appears to be unused.
>
> > > Can you suggest a procedure to test it?
> > Like IMA-measurement and IMA-appraisal, IMA-audit is enabled based on
> > policy. The example IMA policy, below, includes IMA-audit messages for
> > files executed. 'cat' the policy to /sys/kernel/security/ima/policy.
> >
> > /etc/ima/ima-policy:
> > audit func=BPRM_CHECK
> >
> > There's a FireEye blog titled "Extending Linux Executable Logging With
> > The Integrity Measurement Architecture"* that explains how to augment
> > their existing system security analytics with file hashes.
> >
> > *Âhttps://www.fireeye.com/blog/threat-research/2016/11/extending_linux
> > _exec.html
> >
> >
> > Mimi
> >
> > > > If the containerid is defined, include it in the IMA-audit record.
> > > >
> > > > Signed-off-by: Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx>
> > > > ---
> > > >   security/integrity/ima/ima_api.c | 3 +++
> > > >   1 file changed, 3 insertions(+)
> > > >
> > > > diff --git a/security/integrity/ima/ima_api.c b/security/integrity/ima/ima_api.c
> > > > index 33b4458cdbef..41d29a06f28f 100644
> > > > --- a/security/integrity/ima/ima_api.c
> > > > +++ b/security/integrity/ima/ima_api.c
> > > > @@ -335,6 +335,9 @@ void ima_audit_measurement(struct integrity_iint_cache *iint,
> > > >   	audit_log_untrustedstring(ab, algo_hash);
> > > >   
> > > >   	audit_log_task_info(ab, current);
> > > > +	if (audit_containerid_set(current))
> > > > +		audit_log_format(ab, " contid=%llu",
> > > > +				 audit_get_containerid(current));
> > > >   	audit_log_end(ab);
> > > >   
> > > >   	iint->flags |= IMA_AUDITED;
> > > > --
> > > > 2.7.5
> > > - RGB
> - 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