audit: Use struct net not pid_t to remember the network namespce to reply in

While reading through 3.14-rc1 I found a pretty siginficant mishandling
of network namespaces in the recent audit changes.

In struct audit_netlink_list and audit_reply add a reference to the
network namespace of the caller and remove the userspace pid of the
caller.  This cleanly remembers the callers network namespace, and
removes a huge class of races and nasty failure modes that can occur
when attempting to relook up the callers network namespace from a pid_t
(including the caller's network namespace changing, pid wraparound, and
the pid simply not being present).

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Acked-by: Richard Guy Briggs <rgb@redhat.com>
Signed-off-by: Eric Paris <eparis@redhat.com>

kernel/audit.c

@@ -182,7 +182,7 @@ struct audit_buffer {
 
 struct audit_reply {
 	__u32 portid;
-	pid_t pid;
+	struct net *net;
 	struct sk_buff *skb;
 };
 
@@ -500,7 +500,7 @@ int audit_send_list(void *_dest)
 {
 	struct audit_netlink_list *dest = _dest;
 	struct sk_buff *skb;
-	struct net *net = get_net_ns_by_pid(dest->pid);
+	struct net *net = dest->net;
 	struct audit_net *aunet = net_generic(net, audit_net_id);
 
 	/* wait for parent to finish and send an ACK */
@@ -510,6 +510,7 @@ int audit_send_list(void *_dest)
 	while ((skb = __skb_dequeue(&dest->q)) != NULL)
 		netlink_unicast(aunet->nlsk, skb, dest->portid, 0);
 
+	put_net(net);
 	kfree(dest);
 
 	return 0;
@@ -543,7 +544,7 @@ out_kfree_skb:
 static int audit_send_reply_thread(void *arg)
 {
 	struct audit_reply *reply = (struct audit_reply *)arg;
-	struct net *net = get_net_ns_by_pid(reply->pid);
+	struct net *net = reply->net;
 	struct audit_net *aunet = net_generic(net, audit_net_id);
 
 	mutex_lock(&audit_cmd_mutex);
@@ -552,6 +553,7 @@ static int audit_send_reply_thread(void *arg)
 	/* Ignore failure. It'll only happen if the sender goes away,
 	   because our timeout is set to infinite. */
 	netlink_unicast(aunet->nlsk , reply->skb, reply->portid, 0);
+	put_net(net);
 	kfree(reply);
 	return 0;
 }
@@ -583,8 +585,8 @@ static void audit_send_reply(__u32 portid, int seq, int type, int done,
 	if (!skb)
 		goto out;
 
+	reply->net = get_net(current->nsproxy->net_ns);
 	reply->portid = portid;
-	reply->pid = task_pid_vnr(current);
 	reply->skb = skb;
 
 	tsk = kthread_run(audit_send_reply_thread, reply, "audit_send_reply");

kernel/audit.h

@@ -253,7 +253,7 @@ extern void		    audit_panic(const char *message);
 
 struct audit_netlink_list {
 	__u32 portid;
-	pid_t pid;
+	struct net *net;
 	struct sk_buff_head q;
 };
 

kernel/auditfilter.c

@@ -31,6 +31,7 @@
 #include <linux/sched.h>
 #include <linux/slab.h>
 #include <linux/security.h>
+#include <net/net_namespace.h>
 #include "audit.h"
 
 /*
@@ -1085,8 +1086,8 @@ int audit_list_rules_send(__u32 portid, int seq)
 	dest = kmalloc(sizeof(struct audit_netlink_list), GFP_KERNEL);
 	if (!dest)
 		return -ENOMEM;
+	dest->net = get_net(current->nsproxy->net_ns);
 	dest->portid = portid;
-	dest->pid = task_pid_vnr(current);
 	skb_queue_head_init(&dest->q);
 
 	mutex_lock(&audit_filter_mutex);