[PATCH 1/1] audit: log binding and unbinding to netlink multicast

[Steve Grubb <sgrubb@redhat.com>]

Log information about programs connecting and disconnecting to 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. Sample
event:

type=UNKNOWN[1332] msg=audit(1507924331.540:3): pid=1 uid=0
auid=4294967295 tty=(none) ses=4294967295 subj=kernel comm="systemd"
exe="/usr/lib/systemd/systemd" nlnk-grp=1 op=connect res=1

Signed-off-by: sgrubb <sgrubb@redhat.com>
---
 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 0714a66f0e0c..892e63d9f2c1 100644
--- a/include/uapi/linux/audit.h
+++ b/include/uapi/linux/audit.h
@@ -112,6 +112,7 @@
 #define AUDIT_FEATURE_CHANGE	1328	/* audit log listing feature changes */
 #define AUDIT_REPLACE		1329	/* Replace auditd if this packet unanswerd */
 #define AUDIT_KERN_MODULE	1330	/* Kernel Module events */
+#define AUDIT_EVENT_LISTENER	1332	/* 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 1baabc9539b4..3d2461be83a8 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -1476,22 +1476,61 @@ static void audit_receive(struct sk_buff  *skb)
 	mutex_unlock(&audit_cmd_mutex);
 }
 
+/* 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;
+
+	ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_EVENT_LISTENER);
+	if (!ab)
+		return;
+
+	cred = current_cred();
+	tty = audit_get_tty(current);
+
+	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, " nlnk-grp=%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_bind(group, "connect", err);
 
-	return 0;
+	return err;
+}
+
+static void audit_multicast_unbind(struct net *net, int group)
+{
+	audit_log_multicast_bind(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,
 		.flags	= NL_CFG_F_NONROOT_RECV,
 		.groups	= AUDIT_NLGRP_MAX,
+		.unbind = audit_multicast_unbind,
 	};
 
 	struct audit_net *aunet = net_generic(net, audit_net_id);
-- 
2.13.6