[PATCH 2/2] audit: log binding and unbinding to netlink multicast socket

[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.

Signed-off-by: Steve Grubb <sgrubb@redhat.com>
---
 include/uapi/linux/audit.h |  1 +
 kernel/audit.c             | 30 ++++++++++++++++++++++++++++--
 2 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
index d3475e1..bb4555a 100644
--- a/include/uapi/linux/audit.h
+++ b/include/uapi/linux/audit.h
@@ -110,6 +110,7 @@
 #define AUDIT_SECCOMP		1326	/* Secure Computing event */
 #define AUDIT_PROCTITLE		1327	/* Proctitle emit event */
 #define AUDIT_FEATURE_CHANGE	1328	/* audit log listing feature changes */
+#define AUDIT_EVENT_LISTENER	1329	/* 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 29fb38b..3253f1b 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -1135,13 +1135,36 @@ void audit_log_task_simple(struct audit_buffer *ab, struct task_struct *tsk)
 }
 EXPORT_SYMBOL(audit_log_task_simple);
 
+static void audit_log_bind(int group, const char *op, int err)
+{
+	struct audit_buffer *ab;
+
+	ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_EVENT_LISTENER);
+	if (!ab)
+		return;
+
+	audit_log_task_simple(ab, current);
+	audit_log_format(ab, " nlnk-grp=%d", group);
+	audit_log_format(ab, " op=%s", op);
+	audit_log_format(ab, " res=%d", !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)
 {
+	int err = 0;
+
 	if (!capable(CAP_AUDIT_READ))
-		return -EPERM;
+		err = -EPERM;
+	audit_log_bind(group, "connect", err);
 
-	return 0;
+	return err;
+}
+
+static void audit_unbind(struct net *net, int group)
+{
+	audit_log_bind(group, "disconnect", 0);
 }
 
 static int __net_init audit_net_init(struct net *net)
@@ -1151,6 +1176,7 @@ static int __net_init audit_net_init(struct net *net)
 		.bind	= audit_bind,
 		.flags	= NL_CFG_F_NONROOT_RECV,
 		.groups	= AUDIT_NLGRP_MAX,
+		.unbind	= audit_unbind,
 	};
 
 	struct audit_net *aunet = net_generic(net, audit_net_id);
-- 
2.4.3