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

[Paul Moore]

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-Socket-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?

> +       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.

-- 
paul moore
www.paul-moore.com