Re: [PATCH v17 20/23] Audit: Add a new record for multiple subject LSM attributes
On 5/18/2020 3:21 PM, Paul Moore wrote:
On Mon, May 18, 2020 at 4:43 PM Casey Schaufler
<casey(a)schaufler-ca.com> wrote:
> On 5/18/2020 11:02 AM, Stephen Smalley wrote:
>> On Thu, May 14, 2020 at 7:30 PM Casey Schaufler <casey(a)schaufler-ca.com>
wrote:
>>> Create a new audit record type to contain the subject information
>>> when there are multiple security modules that require such data.
>>> This record is emitted before the other records for the event, but
>>> is linked with the same timestamp and serial number.
>>>
>>> Reviewed-by: Kees Cook <keescook(a)chromium.org>
>>> Signed-off-by: Casey Schaufler <casey(a)schaufler-ca.com>
>>> Cc: linux-audit(a)redhat.com
>>> ---
>> With this patch, I see userspace audit records like this one:
>>
>> type=SYSTEM_BOOT msg=audit(1589816792.181:103): pid=789 uid=0
>> auid=4294967295 ses=4294967295 subj=? subj=system_u:system_r:init_t:s0
>> msg=' comm="systemd-update-utmp"
>> exe="/usr/lib/systemd/systemd-update-utmp" hostname=? addr=?
>> terminal=? res=success'
>>
>> I'm guessing that userspace is appending the second subj= field when
>> it sees subj=? or otherwise is missing subj= information?
> I haven't looked at the userspace code, but I expect you're right.
> It looks like there will need to be some change in the userspace
> for the multiple LSM case. The "completion" shown here isn't correct,
> because it only fills in one of the subject attributes, not both.
Wait, didn't we agree on a a "subj=? subj_selinux=XXX
subj_apparmor=YYY subj_smack=ZZZ" format? It looks like there are two
'subj' fields in the record above which is bad, don't do that please.
That's not something that's coming from the kernel.
I'll check again, but I think that everyplace in the kernel that
produces a subj= has been trained to create a type=1420 record
instead.
>> Then we have kernel audit records like this:
>>
>> type=PROCTITLE msg=audit(1589816791.959:101): proctitle=2F7362696E2F617564697463
>> 746C002D52002F6574632F61756469742F61756469742E72756C6573
>> type=SYSCALL msg=audit(1589816791.959:101): arch=c000003e syscall=44
>> success=yes exit=1056 a0=3 a1=7fff9ccc98a0 a2=420 a3=0 items=0
>> ppid=773 pid=783 auid=4294967295 uid=0 gid=0 euid=0 suid=0 fsuid=0
>> egid=0 sgid=0 fsgid=0 tty=(none) ses=4294967295 comm="auditctl"
>> exe="/usr/sbin/auditctl" subj=? key=(null)
>> type=UNKNOWN[1420] msg=audit(1589816791.959:101):
>> subj_selinux=system_u:system_r:unconfined_service_t:s0
>> subj_apparmor==unconfined
>> type=CONFIG_CHANGE msg=audit(1589816791.959:101): auid=4294967295
>> ses=4294967295 subj=? op=add_rule key=(null) list=1 res=1
>> type=UNKNOWN[1420] msg=audit(1589816791.959:101):
>> subj_selinux=system_u:system_r:unconfined_service_t:s0
>> subj_apparmor==unconfined
>>
>> where we are getting multiple copies of the new record type, one for
>> each record type that had subj=?.
> While obviously wasteful, the type=1420 behavior is consistent with
> the subj=? behavior, which is to duplicate the subj= value. I know
> we've got enough hobgoblins in the audit system that we don't need
> to add any more in the name of a foolish consistency.
You need to provide a bit more reason why we need byte-for-byte
duplicate records in a single event. As it currently stands this
looks like something we definitely don't want.
The CONFIG_CHANGE record already duplicates the subj= information
in the SYSCALL record. I just maintained the duplication. You're
right, it's silly to have two identical type=1420 records for the event.
I will have to come up with a mechanism to prevent the duplication.
with luck, there's already a similar case for some other record.
--
paul moore
www.paul-moore.com