[PATCH 2/3] lib/kobject_uevent.c: add uevent forwarding function

["Michael J. Coss" <michael.coss-cfy2TCaE7SFv+uJa97DSA9BPR1lH4CV8@public.gmane.org>]

Adds capability to allow userspace programs to forward a given event to
a specific network namespace as determined by the provided pid.  In
addition, support for a per-namespace kobject_sequence counter was
added.  Sysfs was modified to return the correct event counter based on
the current network namespace.

Signed-off-by: Michael J. Coss <michael.coss-cfy2TCaE7SFv+uJa97DSA9BPR1lH4CV8@public.gmane.org>
---
 include/linux/kobject.h     |  3 ++
 include/net/net_namespace.h |  3 ++
 kernel/ksysfs.c             | 12 ++++++
 lib/kobject_uevent.c        | 90 +++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 108 insertions(+)

diff --git a/include/linux/kobject.h b/include/linux/kobject.h
index 637f670..d1bb509 100644
--- a/include/linux/kobject.h
+++ b/include/linux/kobject.h
@@ -215,6 +215,9 @@ extern struct kobject *firmware_kobj;
 int kobject_uevent(struct kobject *kobj, enum kobject_action action);
 int kobject_uevent_env(struct kobject *kobj, enum kobject_action action,
 			char *envp[]);
+#if defined(CONFIG_UDEVNS) || defined(CONFIG_UDEVNS_MODULE)
+int kobject_uevent_forward(char *buf, size_t len, pid_t pid);
+#endif
 
 __printf(2, 3)
 int add_uevent_var(struct kobj_uevent_env *env, const char *format, ...);
diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
index e951453..a4013e5 100644
--- a/include/net/net_namespace.h
+++ b/include/net/net_namespace.h
@@ -134,6 +134,9 @@ struct net {
 #if IS_ENABLED(CONFIG_MPLS)
 	struct netns_mpls	mpls;
 #endif
+#if defined(CONFIG_UDEVNS) || defined(CONFIG_UDEVNS_MODULE)
+	u64				kevent_seqnum;
+#endif
 	struct sock		*diag_nlsk;
 	atomic_t		fnhe_genid;
 };
diff --git a/kernel/ksysfs.c b/kernel/ksysfs.c
index 6683cce..4bc15fd 100644
--- a/kernel/ksysfs.c
+++ b/kernel/ksysfs.c
@@ -21,6 +21,9 @@
 #include <linux/compiler.h>
 
 #include <linux/rcupdate.h>	/* rcu_expedited */
+#if defined(CONFIG_UDEVNS) || defined(CONFIG_UDEVNS_MODULE)
+#include <net/net_namespace.h>
+#endif
 
 #define KERNEL_ATTR_RO(_name) \
 static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
@@ -33,6 +36,15 @@ static struct kobj_attribute _name##_attr = \
 static ssize_t uevent_seqnum_show(struct kobject *kobj,
 				  struct kobj_attribute *attr, char *buf)
 {
+#if defined(CONFIG_UDEVNS) || defined(CONFIG_UDEVNS_MODULE)
+	pid_t p = task_pid_vnr(current);
+	struct net *n = get_net_ns_by_pid(p);
+
+	if (n != ERR_PTR(-ESRCH)) {
+		if (!net_eq(n, &init_net))
+			return sprintf(buf, "%llu\n", n->kevent_seqnum);
+	}
+#endif
 	return sprintf(buf, "%llu\n", (unsigned long long)uevent_seqnum);
 }
 KERNEL_ATTR_RO(uevent_seqnum);
diff --git a/lib/kobject_uevent.c b/lib/kobject_uevent.c
index d791e33..7589745 100644
--- a/lib/kobject_uevent.c
+++ b/lib/kobject_uevent.c
@@ -379,6 +379,96 @@ int kobject_uevent(struct kobject *kobj, enum kobject_action action)
 }
 EXPORT_SYMBOL_GPL(kobject_uevent);
 
+#if defined(CONFIG_UDEVNS) || defined(CONFIG_UDEVNS_MODULE)
+/**
+ * kobject_uevent_forward - forward event to specified network namespace
+ *
+ * @buf: event buffer
+ * @len: event length
+ * @pid: pid of network namespace
+ *
+ * Returns 0 if kobject_uevent_forward() is completed with success or the
+ * corresponding error when it fails.
+ */
+int kobject_uevent_forward(char *buf, size_t len, pid_t pid)
+{
+	int retval = 0;
+#if defined(CONFIG_NET)
+	struct uevent_sock *ue_sk;
+	struct net *pns;
+	char *p;
+	u64 num;
+
+	/* grab the network namespace of the provided pid */
+	pns = get_net_ns_by_pid(pid);
+	if (pns == ERR_PTR(-ESRCH))
+		return -ESRCH;
+
+	/* find sequence number in buffer */
+	p = buf;
+	num = 0;
+	while (p < (buf + len)) {
+		if (strncmp(p, "SEQNUM=", 7) == 0) {
+			int r;
+
+			p += 7;
+			r = kstrtoull(p, 10, &num);
+			if (r) {
+				put_net(pns);
+				return r;
+			}
+			break;
+		}
+		p += (strlen(p) + 1);
+	}
+
+	/* if we didn't see a valid seqnum, or none was present, return error */
+	if (num == 0) {
+		put_net(pns);
+		return -EINVAL;
+	}
+	/* update per namespace sequence number as needed */
+	if (pns->kevent_seqnum < num)
+		pns->kevent_seqnum = num;
+
+	list_for_each_entry(ue_sk, &uevent_sock_list, list) {
+		struct sock *uevent_sock = ue_sk->sk;
+		struct sk_buff *skb;
+
+		if (!netlink_has_listeners(uevent_sock, 1))
+			continue;
+		/*
+		 * only send to sockets share the same network namespace
+		 * as the passed pid
+		 */
+		if (!net_eq(sock_net(uevent_sock), pns))
+			continue;
+
+		/* allocate message with the maximum possible size */
+		skb = alloc_skb(len, GFP_KERNEL);
+		if (skb) {
+			char *p;
+
+			p = skb_put(skb, len);
+			memcpy(p, buf, len);
+			NETLINK_CB(skb).dst_group = 1;
+			retval = netlink_broadcast(uevent_sock, skb, 0, 1,
+						   GFP_KERNEL);
+
+			/* ENOBUFS should be handled in userspace */
+			if (retval == -ENOBUFS || retval == -ESRCH)
+				retval = 0;
+		} else {
+			retval = -ENOMEM;
+		}
+	}
+	put_net(pns);
+#endif
+	return retval;
+}
+EXPORT_SYMBOL_GPL(kobject_uevent_forward);
+#endif
+
 /**
  * add_uevent_var - add key value string to the environment buffer
  * @env: environment buffer structure
-- 
2.4.6