[RFC][PATCH] audit: log join and part events to the read-only multicast log socket

[Richard Guy Briggs]

Log the event when a client attempts to connect to the netlink audit multicast
socket, requiring CAP_AUDIT_READ capability, binding to the AUDIT_NLGRP_READLOG
group.  Log the disconnect too.

Sample output:
time->Tue Oct  7 14:15:19 2014
type=UNKNOWN[1348] msg=audit(1412705719.316:117): auid=0 uid=0 gid=0 ses=1 pid=3552 comm="audit-multicast" exe="/home/rgb/rgb/git/audit-multicast-listen/audit-multicast-listen" subj=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 group=0 op=connect res=1

Signed-off-by: Richard Guy Briggs <rgb@xxxxxxxxxx>
---
For some reason unbind isn't being called on disconnect.  I suspect missing
plumbing in netlink.  Investigation needed...

 include/uapi/linux/audit.h |    1 +
 kernel/audit.c             |   46 ++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 45 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
index 4d100c8..7fa6e8f 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	1348	/* 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 53bb39b..74c81a7 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -1108,13 +1108,54 @@ static void audit_receive(struct sk_buff  *skb)
 	mutex_unlock(&audit_cmd_mutex);
 }
 
+static void audit_log_bind(int group, char *op, int err)
+{
+	struct audit_buffer *ab;
+	char comm[sizeof(current->comm)];
+	struct mm_struct *mm = current->mm;
+
+	ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_EVENT_LISTENER);
+	if (!ab)
+		return;
+
+	audit_log_format(ab, "auid=%d",
+			from_kuid(&init_user_ns, audit_get_loginuid(current)));
+	audit_log_format(ab, " uid=%d",
+			 from_kuid(&init_user_ns, current_uid()));
+	audit_log_format(ab, " gid=%d",
+			 from_kgid(&init_user_ns, current_gid()));
+	audit_log_format(ab, " ses=%d", audit_get_sessionid(current));
+	audit_log_format(ab, " pid=%d", task_pid_nr(current));
+	audit_log_format(ab, " comm=");
+	audit_log_untrustedstring(ab, get_task_comm(comm, current));
+	if (mm) {
+		down_read(&mm->mmap_sem);
+		if (mm->exe_file)
+			audit_log_d_path(ab, " exe=", &mm->exe_file->f_path);
+		up_read(&mm->mmap_sem);
+	} else 
+		audit_log_format(ab, " exe=(null)");
+	audit_log_task_context(ab); /* subj= */
+	audit_log_format(ab, " group=%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(int group)
 {
+	int err = 0;
+
 	if (!capable(CAP_AUDIT_READ))
-		return -EPERM;
+		err = -EPERM;
+	audit_log_bind(group, "connect", err);
+	return err;
+}
 
-	return 0;
+static void audit_unbind(int group)
+{
+	audit_log_bind(group, "disconnect", 0);
 }
 
 static int __net_init audit_net_init(struct net *net)
@@ -1124,6 +1165,7 @@ 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);
-- 
1.7.1

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