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From:   Richard Guy Briggs <rgb@redhat.com>
To:     Linux-Audit Mailing List <linux-audit@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>
Cc:     Paul Moore <paul@paul-moore.com>, sgrubb@redhat.com,
        omosnace@redhat.com, eparis@parisplace.org,
        Richard Guy Briggs <rgb@redhat.com>
Subject: [PATCH ghak28 V7] audit: log audit netlink multicast bind and unbind events
Date:   Tue, 17 Mar 2020 12:03:23 -0400
Message-Id: <82d85f72416560c155031375fb5b32ac06394c31.1584033222.git.rgb@redhat.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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=PROCTITLE msg=audit(2020-02-18 15:26:50.775:10) : proctitle=/init
type=SYSCALL msg=audit(2020-02-18 15:26:50.775:10) : arch=x86_64 syscall=bind success=yes exit=0 a0=0x19 a1=0x55645c369b70 a2=0xc a3=0x7fff9fedec24 items=0 ppid=0 pid=1 auid=unset uid=root gid=root euid=root suid=root fsuid=root egid=root sgid=root fsgid=root tty=(none) ses=unset comm=systemd exe=/usr/lib/systemd/systemd subj=kernel key=(null)
type=UNKNOWN[1335] msg=audit(2020-02-18 15:26:50.775:10) : 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(2020-02-18 15:28:01.594:307) : proctitle=/usr/bin/perl -w amcast_joinpart/test
type=SYSCALL msg=audit(2020-02-18 15:28:01.594:307) : arch=x86_64 syscall=bind success=yes exit=0 a0=0x7 a1=0x558ebc428be0 a2=0xc a3=0x0 items=0 ppid=642 pid=645 auid=root uid=root gid=root euid=root suid=root fsuid=root egid=root sgid=root fsgid=root tty=ttyS0 ses=1 comm=perl exe=/usr/bin/perl subj=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 key=(null)
type=UNKNOWN[1335] msg=audit(2020-02-18 15:28:01.594:307) : pid=645 uid=root auid=root tty=ttyS0 ses=1 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=PROCTITLE msg=audit(2020-03-17 11:35:31.474:344) : proctitle=/usr/bin/perl -w amcast_joinpart/test 
type=SYSCALL msg=audit(2020-03-17 11:35:31.474:344) : arch=x86_64 syscall=setsockopt success=yes exit=0 a0=0x7 a1=SOL_NETLINK a2=0x2 a3=0x7ffee21ca5f0 items=0 ppid=686 pid=689 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(2020-03-17 11:35:31.474:344) : pid=689 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 

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 at
  https://github.com/linux-audit/audit-kernel/issues/28
With the feature description at
  https://github.com/linux-audit/audit-kernel/wiki/RFE-Audit-Multicast-Socket-Join-Part
The testsuite support is at
  https://github.com/rgbriggs/audit-testsuite/compare/ghak28-mcast-part-join
  https://github.com/linux-audit/audit-testsuite/pull/93
And the userspace support patch is at
  https://github.com/linux-audit/audit-userspace/pull/114

Signed-off-by: Richard Guy Briggs <rgb@redhat.com>

---
Note: subj attrs included due to missing syscall record for disconnect on close
Note: tried refactor of subj attrs, but this is yet another new order.

Changelog:
v7:
- rename audit_log_multicast_bind to audit_log_multicast

v6:
- rebased on 5.6-rc1 audit/next and audit log BPF
- updated patch description sample records

v5:
- rebased on 5.5-rc1 audit/next
- group bind/unbind ops
- add audit context
- justify message number skip
- check audit_enabled
- change field name from nlnk-grp to nl-mcgrp
- fix whitespace issues

v4:
- 2017-10-13 sgrubb
- squash to 1 patch
- rebase on KERN_MODULE event
- open code subj attrs

v3:
- 2016-11-30 sgrubb
- rebase on REPLACE event
- minimize audit_log_format calls
- rename audit_log_bind to audit_log_multicast_bind

v2:
- 2015-07-23 sgrubb
- spin off audit_log_task_simple in seperate patch

v1:
- 2014-10-07 rgb
---
 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 a534d71e689a..9b6a973f4cc3 100644
--- a/include/uapi/linux/audit.h
+++ b/include/uapi/linux/audit.h
@@ -117,6 +117,7 @@
 #define AUDIT_TIME_INJOFFSET	1332	/* Timekeeping offset injected */
 #define AUDIT_TIME_ADJNTPVAL	1333	/* NTP value adjustment */
 #define AUDIT_BPF		1334	/* BPF subsystem */
+#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 b96331e1976d..612bd818f6d7 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(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));
+	audit_put_tty(tty);
+	audit_log_task_context(ab); /* subj= */
+	audit_log_format(ab, " comm=");
+	audit_log_untrustedstring(ab, get_task_comm(comm, current));
+	audit_log_d_path_exe(ab, current->mm); /* exe= */
+	audit_log_format(ab, " nl-mcgrp=%d op=%s res=%d", group, op, !err);
+	audit_log_end(ab);
+}
+
 /* Run custom bind function on netlink socket group connect or bind requests. */
-static int audit_bind(struct net *net, int group)
+static int audit_multicast_bind(struct net *net, int group)
 {
+	int err = 0;
+
 	if (!capable(CAP_AUDIT_READ))
-		return -EPERM;
+		err = -EPERM;
+	audit_log_multicast(group, "connect", err);
+	return err;
+}
 
-	return 0;
+static void audit_multicast_unbind(struct net *net, int group)
+{
+	audit_log_multicast(group, "disconnect", 0);
 }
 
 static int __net_init audit_net_init(struct net *net)
 {
 	struct netlink_kernel_cfg cfg = {
 		.input	= audit_receive,
-		.bind	= audit_bind,
+		.bind	= audit_multicast_bind,
+		.unbind	= audit_multicast_unbind,
 		.flags	= NL_CFG_F_NONROOT_RECV,
 		.groups	= AUDIT_NLGRP_MAX,
 	};
-- 
1.8.3.1