Merge tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-tracegrafted

Pull tracing fixes from Steven Rostedt:

 - Fix error output of boot instance creation failure

   Currently if a boot instance creation fails, instead of printing out
   the name of the instance that failed, it prints "(null)". That is
   because it prints "cur_str" that had already been processed by
   strsep(). Print the saved name instead.

   While at it, print the error code of the failure.

 - Fix use-after-free for same named historgrams

   Histograms can be named so that they can be used in multiple events.
   But if the named histogram has a variable attached, the second event
   that uses the named histogram which duplicates it and needs to free
   the original after duplication leaves the old variable in place and
   still visible. If another histogram uses than variable, it will use
   the stale one which will try to reference the freed duplicate
   histogram and crash the kernel.

   Free the duplicate variables along with the duplicated histogram
   data.

 - Check return value of kthread_run() in event self test

   The events self tests uses a kthread for testing but does not check
   if it succeeded in creating a kthread. If the kthread creation were
   to fail, the code will still try to call kthread_stop() on the error
   returned.

 - Fix race between reading trace_pipe and updating subbuffer size

   If a user is reading the trace_pipe file at the same time they update
   the ring buffer sub-buffer size, can cause the trace_pipe read to
   read stale data. Add trace_access_lock() around updating the ring
   buffer sub-buffer size.

 - Fix eventfs_inode on failure path in creation of the events directory

   In the creation of the "events" directory, if after allocating the
   eventfs_inode a failure is detected, it calls cleanup_ei() which
   calls free_ei(). The free_ei() will test if eventfs_inode being freed
   has no children. It is a bug if it does. But on the failure case of
   the creation of the "events" directory, the children lists have not
   yet been initialized and the free will trigger a warning because
   list_empty() on an uninitialized list returns false.

   Move the initialization into init_ei() where it makes more sense and
   makes sure that a created eventfs_inode has its lists initialized
   upon creation.

 - Check return value of kthread_run() in ftrace direct sample code

   The sample code that shows how to use the ftrace direct calls does
   not test the return of kthread_run() to see if it succeeds. Return a
   failure if the kthread_run() doesn't succeed.

 - Clear user events state on fork in case of alloc failure

   On fork, the child gets a pointer to the parent's user events state.
   It makes a copy of it then updates the child's pointer to it. But if
   the allocation fails, the duplication function leaves the child with
   a pointer to its parent's descriptor. When the child cleans up its
   data, it will free the parent's descriptor while the parent is still
   using it.

   In the duplication function, set the child's user_event_mm to NULL
   before testing if the allocation succeeded, and when it exits it will
   not free the parent's descriptor.

 - Fix retry exhaustion in simple ring buffer reader swap

   simple_ring_buffer_swap_reader_page() starts with retry set to 8 and
   post-decrements it only after a failed link replacement. On the final
   attempt, a successful replacement leaves retry at zero, while a
   failed replacement leaves it at -1.

   But the check for success expects the retry value to be non-zero and
   exits with an error on zero. This is the opposite result. Fix it.

 - Fail nicely when the remote swap_reader_page() returns an error

   Currently, if the swap_reader_page() of a remote buffer fails, it
   triggers a WARN_ON_ONCE() and continues normally. Instead, have it
   exit with an error and a pr_warn() print instead of a full WARNING.

* tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
  ring-buffer: Stop remote reader update when page swap fails
  tracing: Fix retry exhaustion in simple ring buffer reader swap
  tracing/user_events: Clear copied tracing state before fork duplication
  samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-multi-modify
  samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-modify
  eventfs: Initialize ei->children and ei->list in init_ei()
  tracing: Fix use-after-free in trace_pipe read on sub-buffer order change
  tracing: Fix crash passing ERR_PTR to kthread_stop()
  tracing: Fix use-after-free with same-name named triggers
  tracing: Fix logged instance name on creation failure

1 files changed, 851 insertions, 0 deletions

diff --git a/lib/kobject_uevent.c b/lib/kobject_uevent.c
new file mode 100644
index 000000000..ddbc4d748
--- /dev/null
+++ b/lib/kobject_uevent.c
@@ -0,0 +1,851 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * kernel userspace event delivery
+ *
+ * Copyright (C) 2004 Red Hat, Inc.  All rights reserved.
+ * Copyright (C) 2004 Novell, Inc.  All rights reserved.
+ * Copyright (C) 2004 IBM, Inc. All rights reserved.
+ *
+ * Authors:
+ *	Robert Love		<rml@novell.com>
+ *	Kay Sievers		<kay.sievers@vrfy.org>
+ *	Arjan van de Ven	<arjanv@redhat.com>
+ *	Greg Kroah-Hartman	<greg@kroah.com>
+ */
+
+#include <linux/spinlock.h>
+#include <linux/string.h>
+#include <linux/kobject.h>
+#include <linux/export.h>
+#include <linux/kmod.h>
+#include <linux/slab.h>
+#include <linux/socket.h>
+#include <linux/skbuff.h>
+#include <linux/netlink.h>
+#include <linux/uidgid.h>
+#include <linux/uuid.h>
+#include <linux/ctype.h>
+#include <net/sock.h>
+#include <net/netlink.h>
+#include <net/net_namespace.h>
+
+
+atomic64_t uevent_seqnum;
+#ifdef CONFIG_UEVENT_HELPER
+char uevent_helper[UEVENT_HELPER_PATH_LEN] = CONFIG_UEVENT_HELPER_PATH;
+#endif
+
+struct uevent_sock {
+	struct list_head list;
+	struct sock *sk;
+};
+
+#ifdef CONFIG_NET
+static LIST_HEAD(uevent_sock_list);
+/* This lock protects uevent_sock_list */
+static DEFINE_MUTEX(uevent_sock_mutex);
+#endif
+
+/* the strings here must match the enum in include/linux/kobject.h */
+static const char *kobject_actions[] = {
+	[KOBJ_ADD] =		"add",
+	[KOBJ_REMOVE] =		"remove",
+	[KOBJ_CHANGE] =		"change",
+	[KOBJ_MOVE] =		"move",
+	[KOBJ_ONLINE] =		"online",
+	[KOBJ_OFFLINE] =	"offline",
+	[KOBJ_BIND] =		"bind",
+	[KOBJ_UNBIND] =		"unbind",
+};
+
+static int kobject_action_type(const char *buf, size_t count,
+			       enum kobject_action *type,
+			       const char **args)
+{
+	enum kobject_action action;
+	size_t count_first;
+	const char *args_start;
+	int ret = -EINVAL;
+
+	if (count && (buf[count-1] == '\n' || buf[count-1] == '\0'))
+		count--;
+
+	if (!count)
+		goto out;
+
+	args_start = strnchr(buf, count, ' ');
+	if (args_start) {
+		count_first = args_start - buf;
+		args_start = args_start + 1;
+	} else
+		count_first = count;
+
+	for (action = 0; action < ARRAY_SIZE(kobject_actions); action++) {
+		if (strncmp(kobject_actions[action], buf, count_first) != 0)
+			continue;
+		if (kobject_actions[action][count_first] != '\0')
+			continue;
+		if (args)
+			*args = args_start;
+		*type = action;
+		ret = 0;
+		break;
+	}
+out:
+	return ret;
+}
+
+static const char *action_arg_word_end(const char *buf, const char *buf_end,
+				       char delim)
+{
+	const char *next = buf;
+
+	while (next <= buf_end && *next != delim)
+		if (!isalnum(*next++))
+			return NULL;
+
+	if (next == buf)
+		return NULL;
+
+	return next;
+}
+
+static int kobject_action_args(const char *buf, size_t count,
+			       struct kobj_uevent_env **ret_env)
+{
+	struct kobj_uevent_env *env = NULL;
+	const char *next, *buf_end, *key;
+	int key_len;
+	int r = -EINVAL;
+
+	if (count && (buf[count - 1] == '\n' || buf[count - 1] == '\0'))
+		count--;
+
+	if (!count)
+		return -EINVAL;
+
+	env = kzalloc_obj(*env);
+	if (!env)
+		return -ENOMEM;
+
+	/* first arg is UUID */
+	if (count < UUID_STRING_LEN || !uuid_is_valid(buf) ||
+	    add_uevent_var(env, "SYNTH_UUID=%.*s", UUID_STRING_LEN, buf))
+		goto out;
+
+	/*
+	 * the rest are custom environment variables in KEY=VALUE
+	 * format with ' ' delimiter between each KEY=VALUE pair
+	 */
+	next = buf + UUID_STRING_LEN;
+	buf_end = buf + count - 1;
+
+	while (next <= buf_end) {
+		if (*next != ' ')
+			goto out;
+
+		/* skip the ' ', key must follow */
+		key = ++next;
+		if (key > buf_end)
+			goto out;
+
+		buf = next;
+		next = action_arg_word_end(buf, buf_end, '=');
+		if (!next || next > buf_end || *next != '=')
+			goto out;
+		key_len = next - buf;
+
+		/* skip the '=', value must follow */
+		if (++next > buf_end)
+			goto out;
+
+		buf = next;
+		next = action_arg_word_end(buf, buf_end, ' ');
+		if (!next)
+			goto out;
+
+		if (add_uevent_var(env, "SYNTH_ARG_%.*s=%.*s",
+				   key_len, key, (int) (next - buf), buf))
+			goto out;
+	}
+
+	r = 0;
+out:
+	if (r)
+		kfree(env);
+	else
+		*ret_env = env;
+	return r;
+}
+
+/**
+ * kobject_synth_uevent - send synthetic uevent with arguments
+ *
+ * @kobj: struct kobject for which synthetic uevent is to be generated
+ * @buf: buffer containing action type and action args, newline is ignored
+ * @count: length of buffer
+ *
+ * Returns 0 if kobject_synthetic_uevent() is completed with success or the
+ * corresponding error when it fails.
+ */
+int kobject_synth_uevent(struct kobject *kobj, const char *buf, size_t count)
+{
+	char *no_uuid_envp[] = { "SYNTH_UUID=0", NULL };
+	enum kobject_action action;
+	const char *action_args;
+	struct kobj_uevent_env *env;
+	const char *msg = NULL, *devpath;
+	int r;
+
+	r = kobject_action_type(buf, count, &action, &action_args);
+	if (r) {
+		msg = "unknown uevent action string";
+		goto out;
+	}
+
+	if (!action_args) {
+		r = kobject_uevent_env(kobj, action, no_uuid_envp);
+		goto out;
+	}
+
+	r = kobject_action_args(action_args,
+				count - (action_args - buf), &env);
+	if (r == -EINVAL) {
+		msg = "incorrect uevent action arguments";
+		goto out;
+	}
+
+	if (r)
+		goto out;
+
+	r = kobject_uevent_env(kobj, action, env->envp);
+	kfree(env);
+out:
+	if (r) {
+		devpath = kobject_get_path(kobj, GFP_KERNEL);
+		pr_warn("synth uevent: %s: %s\n",
+		       devpath ?: "unknown device",
+		       msg ?: "failed to send uevent");
+		kfree(devpath);
+	}
+	return r;
+}
+
+#ifdef CONFIG_UEVENT_HELPER
+static int kobj_usermode_filter(struct kobject *kobj)
+{
+	const struct kobj_ns_type_operations *ops;
+
+	ops = kobj_ns_ops(kobj);
+	if (ops) {
+		const struct ns_common *init_ns, *ns;
+
+		ns = kobj->ktype->namespace(kobj);
+		init_ns = ops->initial_ns();
+		return ns != init_ns;
+	}
+
+	return 0;
+}
+
+static int init_uevent_argv(struct kobj_uevent_env *env, const char *subsystem)
+{
+	int buffer_size = sizeof(env->buf) - env->buflen;
+	int len;
+
+	len = strscpy(&env->buf[env->buflen], subsystem, buffer_size);
+	if (len < 0) {
+		pr_warn("%s: insufficient buffer space (%u left) for %s\n",
+			__func__, buffer_size, subsystem);
+		return -ENOMEM;
+	}
+
+	env->argv[0] = uevent_helper;
+	env->argv[1] = &env->buf[env->buflen];
+	env->argv[2] = NULL;
+
+	env->buflen += len + 1;
+	return 0;
+}
+
+static void cleanup_uevent_env(struct subprocess_info *info)
+{
+	kfree(info->data);
+}
+#endif
+
+#ifdef CONFIG_NET
+static struct sk_buff *alloc_uevent_skb(struct kobj_uevent_env *env,
+					const char *action_string,
+					const char *devpath)
+{
+	struct netlink_skb_parms *parms;
+	struct sk_buff *skb = NULL;
+	char *scratch;
+	size_t len;
+
+	/* allocate message with maximum possible size */
+	len = strlen(action_string) + strlen(devpath) + 2;
+	skb = alloc_skb(len + env->buflen, GFP_KERNEL);
+	if (!skb)
+		return NULL;
+
+	/* add header */
+	scratch = skb_put(skb, len);
+	sprintf(scratch, "%s@%s", action_string, devpath);
+
+	skb_put_data(skb, env->buf, env->buflen);
+
+	parms = &NETLINK_CB(skb);
+	parms->creds.uid = GLOBAL_ROOT_UID;
+	parms->creds.gid = GLOBAL_ROOT_GID;
+	parms->dst_group = 1;
+	parms->portid = 0;
+
+	return skb;
+}
+
+static int uevent_net_broadcast_untagged(struct kobj_uevent_env *env,
+					 const char *action_string,
+					 const char *devpath)
+{
+	struct sk_buff *skb = NULL;
+	struct uevent_sock *ue_sk;
+	int retval = 0;
+
+	/* send netlink message */
+	mutex_lock(&uevent_sock_mutex);
+	list_for_each_entry(ue_sk, &uevent_sock_list, list) {
+		struct sock *uevent_sock = ue_sk->sk;
+
+		if (!netlink_has_listeners(uevent_sock, 1))
+			continue;
+
+		if (!skb) {
+			retval = -ENOMEM;
+			skb = alloc_uevent_skb(env, action_string, devpath);
+			if (!skb)
+				continue;
+		}
+
+		retval = netlink_broadcast(uevent_sock, skb_get(skb), 0, 1,
+					   GFP_KERNEL);
+		/* ENOBUFS should be handled in userspace */
+		if (retval == -ENOBUFS || retval == -ESRCH)
+			retval = 0;
+	}
+	mutex_unlock(&uevent_sock_mutex);
+	consume_skb(skb);
+
+	return retval;
+}
+
+static int uevent_net_broadcast_tagged(struct sock *usk,
+				       struct kobj_uevent_env *env,
+				       const char *action_string,
+				       const char *devpath)
+{
+	struct user_namespace *owning_user_ns = sock_net(usk)->user_ns;
+	struct sk_buff *skb = NULL;
+	int ret = 0;
+
+	skb = alloc_uevent_skb(env, action_string, devpath);
+	if (!skb)
+		return -ENOMEM;
+
+	/* fix credentials */
+	if (owning_user_ns != &init_user_ns) {
+		struct netlink_skb_parms *parms = &NETLINK_CB(skb);
+		kuid_t root_uid;
+		kgid_t root_gid;
+
+		/* fix uid */
+		root_uid = make_kuid(owning_user_ns, 0);
+		if (uid_valid(root_uid))
+			parms->creds.uid = root_uid;
+
+		/* fix gid */
+		root_gid = make_kgid(owning_user_ns, 0);
+		if (gid_valid(root_gid))
+			parms->creds.gid = root_gid;
+	}
+
+	ret = netlink_broadcast(usk, skb, 0, 1, GFP_KERNEL);
+	/* ENOBUFS should be handled in userspace */
+	if (ret == -ENOBUFS || ret == -ESRCH)
+		ret = 0;
+
+	return ret;
+}
+#endif
+
+static int kobject_uevent_net_broadcast(struct kobject *kobj,
+					struct kobj_uevent_env *env,
+					const char *action_string,
+					const char *devpath)
+{
+	int ret = 0;
+
+#ifdef CONFIG_NET
+	const struct kobj_ns_type_operations *ops;
+	const struct ns_common *ns = NULL;
+
+	ops = kobj_ns_ops(kobj);
+	if (!ops && kobj->kset) {
+		struct kobject *ksobj = &kobj->kset->kobj;
+
+		if (ksobj->parent != NULL)
+			ops = kobj_ns_ops(ksobj->parent);
+	}
+
+	/* kobjects currently only carry network namespace tags and they
+	 * are the only tag relevant here since we want to decide which
+	 * network namespaces to broadcast the uevent into.
+	 */
+	if (ops && ops->netlink_ns && kobj->ktype->namespace)
+		if (ops->type == KOBJ_NS_TYPE_NET)
+			ns = kobj->ktype->namespace(kobj);
+
+	if (!ns)
+		ret = uevent_net_broadcast_untagged(env, action_string,
+						    devpath);
+	else {
+		const struct net *net = container_of(ns, struct net, ns);
+
+		ret = uevent_net_broadcast_tagged(net->uevent_sock->sk, env,
+						  action_string, devpath);
+	}
+#endif
+
+	return ret;
+}
+
+static void zap_modalias_env(struct kobj_uevent_env *env)
+{
+	static const char modalias_prefix[] = "MODALIAS=";
+	size_t len;
+	int i, j;
+
+	for (i = 0; i < env->envp_idx;) {
+		if (strncmp(env->envp[i], modalias_prefix,
+			    sizeof(modalias_prefix) - 1)) {
+			i++;
+			continue;
+		}
+
+		len = strlen(env->envp[i]) + 1;
+
+		if (i != env->envp_idx - 1) {
+			/* @env->envp[] contains pointers to @env->buf[]
+			 * with @env->buflen chars, and we are removing
+			 * variable MODALIAS here pointed by @env->envp[i]
+			 * with length @len as shown below:
+			 *
+			 * 0               @env->buf[]      @env->buflen
+			 * ---------------------------------------------
+			 * ^             ^              ^              ^
+			 * |             |->   @len   <-| target block |
+			 * @env->envp[0] @env->envp[i]  @env->envp[i + 1]
+			 *
+			 * so the "target block" indicated above is moved
+			 * backward by @len, and its right size is
+			 * @env->buflen - (@env->envp[i + 1] - @env->envp[0]).
+			 */
+			memmove(env->envp[i], env->envp[i + 1],
+				env->buflen - (env->envp[i + 1] - env->envp[0]));
+
+			for (j = i; j < env->envp_idx - 1; j++)
+				env->envp[j] = env->envp[j + 1] - len;
+		}
+
+		env->envp_idx--;
+		env->buflen -= len;
+	}
+}
+
+/**
+ * kobject_uevent_env - send an uevent with environmental data
+ *
+ * @kobj: struct kobject that the action is happening to
+ * @action: action that is happening
+ * @envp_ext: pointer to environmental data
+ *
+ * Returns 0 if kobject_uevent_env() is completed with success or the
+ * corresponding error when it fails.
+ */
+int kobject_uevent_env(struct kobject *kobj, enum kobject_action action,
+		       char *envp_ext[])
+{
+	struct kobj_uevent_env *env;
+	const char *action_string = kobject_actions[action];
+	const char *devpath = NULL;
+	const char *subsystem;
+	struct kobject *top_kobj;
+	struct kset *kset;
+	const struct kset_uevent_ops *uevent_ops;
+	int i = 0;
+	int retval = 0;
+
+	/*
+	 * Mark "remove" event done regardless of result, for some subsystems
+	 * do not want to re-trigger "remove" event via automatic cleanup.
+	 */
+	if (action == KOBJ_REMOVE)
+		kobj->state_remove_uevent_sent = 1;
+
+	pr_debug("kobject: '%s' (%p): %s\n",
+		 kobject_name(kobj), kobj, __func__);
+
+	/* search the kset we belong to */
+	top_kobj = kobj;
+	while (!top_kobj->kset && top_kobj->parent)
+		top_kobj = top_kobj->parent;
+
+	if (!top_kobj->kset) {
+		pr_debug("kobject: '%s' (%p): %s: attempted to send uevent "
+			 "without kset!\n", kobject_name(kobj), kobj,
+			 __func__);
+		return -EINVAL;
+	}
+
+	kset = top_kobj->kset;
+	uevent_ops = kset->uevent_ops;
+
+	/* skip the event, if uevent_suppress is set*/
+	if (kobj->uevent_suppress) {
+		pr_debug("kobject: '%s' (%p): %s: uevent_suppress "
+				 "caused the event to drop!\n",
+				 kobject_name(kobj), kobj, __func__);
+		return 0;
+	}
+	/* skip the event, if the filter returns zero. */
+	if (uevent_ops && uevent_ops->filter)
+		if (!uevent_ops->filter(kobj)) {
+			pr_debug("kobject: '%s' (%p): %s: filter function "
+				 "caused the event to drop!\n",
+				 kobject_name(kobj), kobj, __func__);
+			return 0;
+		}
+
+	/* originating subsystem */
+	if (uevent_ops && uevent_ops->name)
+		subsystem = uevent_ops->name(kobj);
+	else
+		subsystem = kobject_name(&kset->kobj);
+	if (!subsystem) {
+		pr_debug("kobject: '%s' (%p): %s: unset subsystem caused the "
+			 "event to drop!\n", kobject_name(kobj), kobj,
+			 __func__);
+		return 0;
+	}
+
+	/* environment buffer */
+	env = kzalloc_obj(struct kobj_uevent_env);
+	if (!env)
+		return -ENOMEM;
+
+	/* complete object path */
+	devpath = kobject_get_path(kobj, GFP_KERNEL);
+	if (!devpath) {
+		retval = -ENOENT;
+		goto exit;
+	}
+
+	/* default keys */
+	retval = add_uevent_var(env, "ACTION=%s", action_string);
+	if (retval)
+		goto exit;
+	retval = add_uevent_var(env, "DEVPATH=%s", devpath);
+	if (retval)
+		goto exit;
+	retval = add_uevent_var(env, "SUBSYSTEM=%s", subsystem);
+	if (retval)
+		goto exit;
+
+	/* keys passed in from the caller */
+	if (envp_ext) {
+		for (i = 0; envp_ext[i]; i++) {
+			retval = add_uevent_var(env, "%s", envp_ext[i]);
+			if (retval)
+				goto exit;
+		}
+	}
+
+	/* let the kset specific function add its stuff */
+	if (uevent_ops && uevent_ops->uevent) {
+		retval = uevent_ops->uevent(kobj, env);
+		if (retval) {
+			pr_debug("kobject: '%s' (%p): %s: uevent() returned "
+				 "%d\n", kobject_name(kobj), kobj,
+				 __func__, retval);
+			goto exit;
+		}
+	}
+
+	switch (action) {
+	case KOBJ_ADD:
+		/*
+		 * Mark "add" event so we can make sure we deliver "remove"
+		 * event to userspace during automatic cleanup. If
+		 * the object did send an "add" event, "remove" will
+		 * automatically generated by the core, if not already done
+		 * by the caller.
+		 */
+		kobj->state_add_uevent_sent = 1;
+		break;
+
+	case KOBJ_UNBIND:
+		zap_modalias_env(env);
+		break;
+
+	default:
+		break;
+	}
+
+	/* we will send an event, so request a new sequence number */
+	retval = add_uevent_var(env, "SEQNUM=%llu",
+				atomic64_inc_return(&uevent_seqnum));
+	if (retval)
+		goto exit;
+
+	retval = kobject_uevent_net_broadcast(kobj, env, action_string,
+					      devpath);
+
+#ifdef CONFIG_UEVENT_HELPER
+	/* call uevent_helper, usually only enabled during early boot */
+	if (uevent_helper[0] && !kobj_usermode_filter(kobj)) {
+		struct subprocess_info *info;
+
+		retval = add_uevent_var(env, "HOME=/");
+		if (retval)
+			goto exit;
+		retval = add_uevent_var(env,
+					"PATH=/sbin:/bin:/usr/sbin:/usr/bin");
+		if (retval)
+			goto exit;
+		retval = init_uevent_argv(env, subsystem);
+		if (retval)
+			goto exit;
+
+		retval = -ENOMEM;
+		info = call_usermodehelper_setup(env->argv[0], env->argv,
+						 env->envp, GFP_KERNEL,
+						 NULL, cleanup_uevent_env, env);
+		if (info) {
+			retval = call_usermodehelper_exec(info, UMH_NO_WAIT);
+			env = NULL;	/* freed by cleanup_uevent_env */
+		}
+	}
+#endif
+
+exit:
+	kfree(devpath);
+	kfree(env);
+	return retval;
+}
+EXPORT_SYMBOL_GPL(kobject_uevent_env);
+
+/**
+ * kobject_uevent - notify userspace by sending an uevent
+ *
+ * @kobj: struct kobject that the action is happening to
+ * @action: action that is happening
+ *
+ * Returns 0 if kobject_uevent() is completed with success or the
+ * corresponding error when it fails.
+ */
+int kobject_uevent(struct kobject *kobj, enum kobject_action action)
+{
+	return kobject_uevent_env(kobj, action, NULL);
+}
+EXPORT_SYMBOL_GPL(kobject_uevent);
+
+/**
+ * add_uevent_var - add key value string to the environment buffer
+ * @env: environment buffer structure
+ * @format: printf format for the key=value pair
+ *
+ * Returns 0 if environment variable was added successfully or -ENOMEM
+ * if no space was available.
+ */
+int add_uevent_var(struct kobj_uevent_env *env, const char *format, ...)
+{
+	va_list args;
+	int len;
+
+	if (env->envp_idx >= ARRAY_SIZE(env->envp)) {
+		WARN(1, KERN_ERR "add_uevent_var: too many keys\n");
+		return -ENOMEM;
+	}
+
+	va_start(args, format);
+	len = vsnprintf(&env->buf[env->buflen],
+			sizeof(env->buf) - env->buflen,
+			format, args);
+	va_end(args);
+
+	if (len >= (sizeof(env->buf) - env->buflen)) {
+		WARN(1, KERN_ERR "add_uevent_var: buffer size too small\n");
+		return -ENOMEM;
+	}
+
+	env->envp[env->envp_idx++] = &env->buf[env->buflen];
+	env->buflen += len + 1;
+	return 0;
+}
+EXPORT_SYMBOL_GPL(add_uevent_var);
+
+#if defined(CONFIG_NET)
+static int uevent_net_broadcast(struct sock *usk, struct sk_buff *skb,
+				struct netlink_ext_ack *extack)
+{
+	/* u64 to chars: 2^64 - 1 = 21 chars */
+	char buf[sizeof("SEQNUM=") + 21];
+	struct sk_buff *skbc;
+	int ret;
+
+	/* bump and prepare sequence number */
+	ret = snprintf(buf, sizeof(buf), "SEQNUM=%llu",
+		       atomic64_inc_return(&uevent_seqnum));
+	if (ret < 0 || (size_t)ret >= sizeof(buf))
+		return -ENOMEM;
+	ret++;
+
+	/* verify message does not overflow */
+	if ((skb->len + ret) > UEVENT_BUFFER_SIZE) {
+		NL_SET_ERR_MSG(extack, "uevent message too big");
+		return -EINVAL;
+	}
+
+	/* copy skb and extend to accommodate sequence number */
+	skbc = skb_copy_expand(skb, 0, ret, GFP_KERNEL);
+	if (!skbc)
+		return -ENOMEM;
+
+	/* append sequence number */
+	skb_put_data(skbc, buf, ret);
+
+	/* remove msg header */
+	skb_pull(skbc, NLMSG_HDRLEN);
+
+	/* set portid 0 to inform userspace message comes from kernel */
+	NETLINK_CB(skbc).portid = 0;
+	NETLINK_CB(skbc).dst_group = 1;
+
+	ret = netlink_broadcast(usk, skbc, 0, 1, GFP_KERNEL);
+	/* ENOBUFS should be handled in userspace */
+	if (ret == -ENOBUFS || ret == -ESRCH)
+		ret = 0;
+
+	return ret;
+}
+
+static int uevent_net_rcv_skb(struct sk_buff *skb, struct nlmsghdr *nlh,
+			      struct netlink_ext_ack *extack)
+{
+	struct net *net;
+	int ret;
+
+	if (!nlmsg_data(nlh))
+		return -EINVAL;
+
+	/*
+	 * Verify that we are allowed to send messages to the target
+	 * network namespace. The caller must have CAP_SYS_ADMIN in the
+	 * owning user namespace of the target network namespace.
+	 */
+	net = sock_net(NETLINK_CB(skb).sk);
+	if (!netlink_ns_capable(skb, net->user_ns, CAP_SYS_ADMIN)) {
+		NL_SET_ERR_MSG(extack, "missing CAP_SYS_ADMIN capability");
+		return -EPERM;
+	}
+
+	ret = uevent_net_broadcast(net->uevent_sock->sk, skb, extack);
+
+	return ret;
+}
+
+static void uevent_net_rcv(struct sk_buff *skb)
+{
+	netlink_rcv_skb(skb, &uevent_net_rcv_skb);
+}
+
+static int uevent_net_init(struct net *net)
+{
+	struct uevent_sock *ue_sk;
+	struct netlink_kernel_cfg cfg = {
+		.groups	= 1,
+		.input = uevent_net_rcv,
+		.flags	= NL_CFG_F_NONROOT_RECV
+	};
+
+	ue_sk = kzalloc_obj(*ue_sk);
+	if (!ue_sk)
+		return -ENOMEM;
+
+	ue_sk->sk = netlink_kernel_create(net, NETLINK_KOBJECT_UEVENT, &cfg);
+	if (!ue_sk->sk) {
+		pr_err("kobject_uevent: unable to create netlink socket!\n");
+		kfree(ue_sk);
+		return -ENODEV;
+	}
+
+	net->uevent_sock = ue_sk;
+
+	/* Restrict uevents to initial user namespace. */
+	if (sock_net(ue_sk->sk)->user_ns == &init_user_ns) {
+		mutex_lock(&uevent_sock_mutex);
+		list_add_tail(&ue_sk->list, &uevent_sock_list);
+		mutex_unlock(&uevent_sock_mutex);
+	}
+
+	return 0;
+}
+
+static void uevent_net_exit(struct net *net)
+{
+	struct uevent_sock *ue_sk = net->uevent_sock;
+
+	if (sock_net(ue_sk->sk)->user_ns == &init_user_ns) {
+		mutex_lock(&uevent_sock_mutex);
+		list_del(&ue_sk->list);
+		mutex_unlock(&uevent_sock_mutex);
+	}
+
+	netlink_kernel_release(ue_sk->sk);
+	kfree(ue_sk);
+}
+
+static struct pernet_operations uevent_net_ops = {
+	.init	= uevent_net_init,
+	.exit	= uevent_net_exit,
+};
+
+static int __init kobject_uevent_init(void)
+{
+	return register_pernet_subsys(&uevent_net_ops);
+}
+
+
+postcore_initcall(kobject_uevent_init);
+#endif
+
+#ifdef CONFIG_UEVENT_HELPER
+static const struct ctl_table uevent_helper_sysctl_table[] = {
+	{
+		.procname	= "hotplug",
+		.data		= &uevent_helper,
+		.maxlen		= UEVENT_HELPER_PATH_LEN,
+		.mode		= 0644,
+		.proc_handler	= proc_dostring,
+	},
+};
+
+static int __init init_uevent_helper_sysctl(void)
+{
+	register_sysctl_init("kernel", uevent_helper_sysctl_table);
+	return 0;
+}
+
+postcore_initcall(init_uevent_helper_sysctl);
+#endif