Re: auditd and CAP_AUDIT_READ
On 2018-11-15 09:51, Steve Grubb wrote:
On Wed, 14 Nov 2018 19:57:07 -0500
Richard Guy Briggs <rgb(a)redhat.com> wrote:
> Hi Steve,
>
> In commit 183775f155cb96d8012c2d493041a03f1b825b2f ("Do capabilities
> check rather than uid") a switch was made from checking "getuid() !=
> 0" to checking CAP_AUDIT_CONTROL and CAP_AUDIT_READ via
> audit_can_control() and audit_can_read().
>
> Does auditd use the multicast socket?
No. It uses the prime guaranteed delivery netlink connection.
So all it needs is CAP_AUDIT_CONTROL as it did previously. Other user
applications that write AUDIT_USER* messages need CAP_AUDIT_WRITE.
CAP_AUDIT_READ gates the bind function which is used to join a multicast
group (of which there is only one).
> If not, there is no need for it to check or have CAP_AUDIT_READ
I thought that the prime audit connection requires a capability check
to ensure a process without proper privilege does not replace the audit
daemon...since that's now possible. Are there privilege checks for who
can connect to the audit socket? Shouldn't that process also have
CAP_AUDIT_READ since that is what it will be doing?
The only cap that will let a daemon be checked for replacement is
CAP_AUDIT_CONTROL. CAP_AUDIT_READ is only used for the unreliable
reception of multicast audit log records.
The unicast socket is gated by CAP_AUDIT_CONTROL and CAP_AUDIT_WRITE.
The multicast read-only unreliable socket is gated by CAP_AUDIT_READ.
> Having audit_can_read() available in lib/libaudit.c is
certainly
> useful regardless for other potential libaudit users like systemd.
I have never tried to make libaudit work with multicast sockets because
I'm against the whole concept.
In hindsight, so am I. This was one of the first things I implemented
when I started working on audit with Eric's enthusiasm and encouragement.
-Steve
- RGB
--
Richard Guy Briggs <rgb(a)redhat.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