linux/lib/kobject_uevent.c
Tetsuo Handa c03a0fd0b6 kobject: Don't trigger kobject_uevent(KOBJ_REMOVE) twice.
syzbot is hitting use-after-free bug in uinput module [1]. This is because
kobject_uevent(KOBJ_REMOVE) is called again due to commit 0f4dafc056
("Kobject: auto-cleanup on final unref") after memory allocation fault
injection made kobject_uevent(KOBJ_REMOVE) from device_del() from
input_unregister_device() fail, while uinput_destroy_device() is expecting
that kobject_uevent(KOBJ_REMOVE) is not called after device_del() from
input_unregister_device() completed.

That commit intended to catch cases where nobody even attempted to send
"remove" uevents. But there is no guarantee that an event will ultimately
be sent. We are at the point of no return as far as the rest of the kernel
is concerned; there are no repeats or do-overs.

Also, it is not clear whether some subsystem depends on that commit.
If no subsystem depends on that commit, it will be better to remove
the state_{add,remove}_uevent_sent logic. But we don't want to risk
a regression (in a patch which will be backported) by trying to remove
that logic. Therefore, as a first step, let's avoid the use-after-free bug
by making sure that kobject_uevent(KOBJ_REMOVE) won't be triggered twice.

[1] https://syzkaller.appspot.com/bug?id=8b17c134fe938bbddd75a45afaa9e68af43a362d

Reported-by: syzbot <syzbot+f648cfb7e0b52bf7ae32@syzkaller.appspotmail.com>
Analyzed-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Fixes: 0f4dafc056 ("Kobject: auto-cleanup on final unref")
Cc: Kay Sievers <kay@vrfy.org>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2019-04-01 07:37:12 +02:00

815 lines
19 KiB
C

// 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>
u64 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);
#endif
/* This lock protects uevent_seqnum and uevent_sock_list */
static DEFINE_MUTEX(uevent_sock_mutex);
/* 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(sizeof(*env), GFP_KERNEL);
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 void *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 len;
len = strlcpy(&env->buf[env->buflen], subsystem,
sizeof(env->buf) - env->buflen);
if (len >= (sizeof(env->buf) - env->buflen)) {
WARN(1, KERN_ERR "init_uevent_argv: buffer size too small\n");
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 */
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;
}
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 net *net = 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)
net = kobj->ktype->namespace(kobj);
if (!net)
ret = uevent_net_broadcast_untagged(env, action_string,
devpath);
else
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) {
memmove(env->envp[i], env->envp[i + 1],
env->buflen - len);
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(kset, 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(kset, 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(sizeof(struct kobj_uevent_env), GFP_KERNEL);
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(kset, 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;
}
mutex_lock(&uevent_sock_mutex);
/* we will send an event, so request a new sequence number */
retval = add_uevent_var(env, "SEQNUM=%llu", ++uevent_seqnum);
if (retval) {
mutex_unlock(&uevent_sock_mutex);
goto exit;
}
retval = kobject_uevent_net_broadcast(kobj, env, action_string,
devpath);
mutex_unlock(&uevent_sock_mutex);
#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", ++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;
}
mutex_lock(&uevent_sock_mutex);
ret = uevent_net_broadcast(net->uevent_sock->sk, skb, extack);
mutex_unlock(&uevent_sock_mutex);
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(sizeof(*ue_sk), GFP_KERNEL);
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