Re: [PATCH ghak28 V4] audit: log audit netlink multicast bind and unbind events

[Steve Grubb]

On Wednesday, January 22, 2020 5:40:10 PM EST Paul Moore wrote:
> On Fri, Jan 17, 2020 at 3:21 PM Richard Guy Briggs <rgb@xxxxxxxxxx> wrote:
> > Log information about programs connecting to and disconnecting from the
> > audit netlink multicast socket. This is needed so that during
> > investigations a security officer can tell who or what had access to the
> > audit trail.  This helps to meet the FAU_SAR.2 requirement for Common
> > Criteria.  Here is the systemd startup event:
> > 
> > type=UNKNOWN[1335] msg=audit(2020-01-17 10:30:33.731:6) : pid=1 uid=root
> > auid=unset tty=(none) ses=unset subj=kernel comm=systemd
> > exe=/usr/lib/systemd/systemd nl-mcgrp=1 op=connect res=yes
> > 
> > And the events from the test suite:
> > 
> > type=PROCTITLE msg=audit(2020-01-17 10:36:24.050:294) :
> > proctitle=/usr/bin/perl -w amcast_joinpart/test type=SOCKADDR
> > msg=audit(2020-01-17 10:36:24.050:294) : saddr={ saddr_fam=netlink
> > nlnk-fam=16 nlnk-pid=0 } type=SYSCALL msg=audit(2020-01-17
> > 10:36:24.050:294) : arch=x86_64 syscall=bind success=yes exit=0 a0=0x7
> > a1=0x55d65cb79090 a2=0xc a3=0x0 items=0 ppid=671 pid=674 auid=root
> > uid=root gid=root euid=root suid=root fsuid=root egid=root sgid=root
> > fsgid=root tty=ttyS0 ses=3 comm=perl exe=/usr/bin/perl
> > subj=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 key=(null)
> > type=UNKNOWN[1335] msg=audit(2020-01-17 10:36:24.050:294) : pid=674
> > uid=root auid=root tty=ttyS0 ses=3
> > subj=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 comm=perl
> > exe=/usr/bin/perl nl-mcgrp=1 op=connect res=yes
> > 
> > type=UNKNOWN[1335] msg=audit(2020-01-17 10:36:24.051:295) : pid=674
> > uid=root auid=root tty=ttyS0 ses=3
> > subj=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 comm=perl
> > exe=/usr/bin/perl nl-mcgrp=1 op=disconnect res=yes> 
> > Please see the upstream issue tracker:
> >   https://github.com/linux-audit/audit-kernel/issues/28
> >   https://github.com/linux-audit/audit-kernel/wiki/RFE-Audit-Multicast-So
> >   cket-Join-Part
> >   https://github.com/rgbriggs/audit-testsuite/compare/ghak28-mcast-part-> >   join> 
> > Signed-off-by: Richard Guy Briggs <rgb@xxxxxxxxxx>
> > 
> > ---
> > Note: msg type 1334 was skipped due to BPF accepted in another tree.
> > Note: v5 due to previous 2014-10-07, 2015-07-23, 2016-11-30, 2017-10-13
> > Note: subj attrs included due to missing syscall record for systemd
> > (audit=1) Note: tried refactor of subj attrs, but this is yet another
> > new order. ---
> > 
> >  include/uapi/linux/audit.h |  1 +
> >  kernel/audit.c             | 48
> >  ++++++++++++++++++++++++++++++++++++++++++---- 2 files changed, 45
> >  insertions(+), 4 deletions(-)
> > 
> > diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
> > index 3ad935527177..67fb24472dc2 100644
> > --- a/include/uapi/linux/audit.h
> > +++ b/include/uapi/linux/audit.h
> > @@ -116,6 +116,7 @@
> > 
> >  #define AUDIT_FANOTIFY         1331    /* Fanotify access decision */
> >  #define AUDIT_TIME_INJOFFSET   1332    /* Timekeeping offset injected */
> >  #define AUDIT_TIME_ADJNTPVAL   1333    /* NTP value adjustment */
> > 
> > +#define AUDIT_EVENT_LISTENER   1335    /* Task joined multicast read
> > socket */> 
> >  #define AUDIT_AVC              1400    /* SE Linux avc denial or grant
> >  */
> >  #define AUDIT_SELINUX_ERR      1401    /* Internal SE Linux Errors */
> > 
> > diff --git a/kernel/audit.c b/kernel/audit.c
> > index 17b0d523afb3..478259f3fa53 100644
> > --- a/kernel/audit.c
> > +++ b/kernel/audit.c
> > @@ -1520,20 +1520,60 @@ static void audit_receive(struct sk_buff  *skb)
> > 
> >         audit_ctl_unlock();
> >  
> >  }
> > 
> > +/* Log information about who is connecting to the audit multicast socket
> > */ +static void audit_log_multicast_bind(int group, const char *op, int
> > err) +{
> > +       const struct cred *cred;
> > +       struct tty_struct *tty;
> > +       char comm[sizeof(current->comm)];
> > +       struct audit_buffer *ab;
> > +
> > +       if (!audit_enabled)
> > +               return;
> > +
> > +       ab = audit_log_start(audit_context(), GFP_KERNEL,
> > AUDIT_EVENT_LISTENER); +       if (!ab)
> > +               return;
> > +
> > +       cred = current_cred();
> > +       tty = audit_get_tty();
> > +       audit_log_format(ab, "pid=%u uid=%u auid=%u tty=%s ses=%u",
> > +                        task_pid_nr(current),
> > +                        from_kuid(&init_user_ns, cred->uid),
> > +                        from_kuid(&init_user_ns,
> > audit_get_loginuid(current)), +                        tty ?
> > tty_name(tty) : "(none)",
> > +                        audit_get_sessionid(current));
> 
> Don't we already get all of that information as part of the syscall record?

We don't want or need a syscall record. It doesn't add anything to the 
necessary information. Also, when we have syscall records, people expect that 
they obey the syscall auditing. Especially wrt "never" audit rules.


> > +       audit_put_tty(tty);
> > +       audit_log_task_context(ab); /* subj= */
> 
> Also part of the syscall record.
> 
> > +       audit_log_format(ab, " comm=");
> > +       audit_log_untrustedstring(ab, get_task_comm(comm, current));
> 
> Again.
> 
> > +       audit_log_d_path_exe(ab, current->mm); /* exe= */
> 
> Again.
> 
> > +       audit_log_format(ab, " nl-mcgrp=%d op=%s res=%d", group, op,
> > !err);
> This part is new ;)
> 
> > +       audit_log_end(ab);
> > +}
> 
> I'm pretty sure these are the same arguments I made when Steve posted
> a prior version of this patch.

No. You didn't mind it then. What you objected to was that I wrote a helper 
function that could be used by future audit events to start a format 
standardization process.

The event looks good to me. Ack for the format being acceptable to existing 
tools.

-Steve