Merge tag 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost

[mirror_ubuntu-bionic-kernel.git] / kernel / umh.c

/*
 * umh - the kernel usermode helper
 */
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/sched/task.h>
#include <linux/binfmts.h>
#include <linux/syscalls.h>
#include <linux/unistd.h>
#include <linux/kmod.h>
#include <linux/slab.h>
#include <linux/completion.h>
#include <linux/cred.h>
#include <linux/file.h>
#include <linux/fdtable.h>
#include <linux/workqueue.h>
#include <linux/security.h>
#include <linux/mount.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/resource.h>
#include <linux/notifier.h>
#include <linux/suspend.h>
#include <linux/rwsem.h>
#include <linux/ptrace.h>
#include <linux/async.h>
#include <linux/uaccess.h>

#include <trace/events/module.h>

#define CAP_BSET        (void *)1
#define CAP_PI          (void *)2

static kernel_cap_t usermodehelper_bset = CAP_FULL_SET;
static kernel_cap_t usermodehelper_inheritable = CAP_FULL_SET;
static DEFINE_SPINLOCK(umh_sysctl_lock);
static DECLARE_RWSEM(umhelper_sem);

static void call_usermodehelper_freeinfo(struct subprocess_info *info)
{
        if (info->cleanup)
                (*info->cleanup)(info);
        kfree(info);
}

static void umh_complete(struct subprocess_info *sub_info)
{
        struct completion *comp = xchg(&sub_info->complete, NULL);
        /*
         * See call_usermodehelper_exec(). If xchg() returns NULL
         * we own sub_info, the UMH_KILLABLE caller has gone away
         * or the caller used UMH_NO_WAIT.
         */
        if (comp)
                complete(comp);
        else
                call_usermodehelper_freeinfo(sub_info);
}

/*
 * This is the task which runs the usermode application
 */
static int call_usermodehelper_exec_async(void *data)
{
        struct subprocess_info *sub_info = data;
        struct cred *new;
        int retval;

        spin_lock_irq(&current->sighand->siglock);
        flush_signal_handlers(current, 1);
        spin_unlock_irq(&current->sighand->siglock);

        /*
         * Our parent (unbound workqueue) runs with elevated scheduling
         * priority. Avoid propagating that into the userspace child.
         */
        set_user_nice(current, 0);

        retval = -ENOMEM;
        new = prepare_kernel_cred(current);
        if (!new)
                goto out;

        spin_lock(&umh_sysctl_lock);
        new->cap_bset = cap_intersect(usermodehelper_bset, new->cap_bset);
        new->cap_inheritable = cap_intersect(usermodehelper_inheritable,
                                             new->cap_inheritable);
        spin_unlock(&umh_sysctl_lock);

        if (sub_info->init) {
                retval = sub_info->init(sub_info, new);
                if (retval) {
                        abort_creds(new);
                        goto out;
                }
        }

        commit_creds(new);

        retval = do_execve(getname_kernel(sub_info->path),
                           (const char __user *const __user *)sub_info->argv,
                           (const char __user *const __user *)sub_info->envp);
out:
        sub_info->retval = retval;
        /*
         * call_usermodehelper_exec_sync() will call umh_complete
         * if UHM_WAIT_PROC.
         */
        if (!(sub_info->wait & UMH_WAIT_PROC))
                umh_complete(sub_info);
        if (!retval)
                return 0;
        do_exit(0);
}

/* Handles UMH_WAIT_PROC.  */
static void call_usermodehelper_exec_sync(struct subprocess_info *sub_info)
{
        pid_t pid;

        /* If SIGCLD is ignored sys_wait4 won't populate the status. */
        kernel_sigaction(SIGCHLD, SIG_DFL);
        pid = kernel_thread(call_usermodehelper_exec_async, sub_info, SIGCHLD);
        if (pid < 0) {
                sub_info->retval = pid;
        } else {
                int ret = -ECHILD;
                /*
                 * Normally it is bogus to call wait4() from in-kernel because
                 * wait4() wants to write the exit code to a userspace address.
                 * But call_usermodehelper_exec_sync() always runs as kernel
                 * thread (workqueue) and put_user() to a kernel address works
                 * OK for kernel threads, due to their having an mm_segment_t
                 * which spans the entire address space.
                 *
                 * Thus the __user pointer cast is valid here.
                 */
                sys_wait4(pid, (int __user *)&ret, 0, NULL);

                /*
                 * If ret is 0, either call_usermodehelper_exec_async failed and
                 * the real error code is already in sub_info->retval or
                 * sub_info->retval is 0 anyway, so don't mess with it then.
                 */
                if (ret)
                        sub_info->retval = ret;
        }

        /* Restore default kernel sig handler */
        kernel_sigaction(SIGCHLD, SIG_IGN);

        umh_complete(sub_info);
}

/*
 * We need to create the usermodehelper kernel thread from a task that is affine
 * to an optimized set of CPUs (or nohz housekeeping ones) such that they
 * inherit a widest affinity irrespective of call_usermodehelper() callers with
 * possibly reduced affinity (eg: per-cpu workqueues). We don't want
 * usermodehelper targets to contend a busy CPU.
 *
 * Unbound workqueues provide such wide affinity and allow to block on
 * UMH_WAIT_PROC requests without blocking pending request (up to some limit).
 *
 * Besides, workqueues provide the privilege level that caller might not have
 * to perform the usermodehelper request.
 *
 */
static void call_usermodehelper_exec_work(struct work_struct *work)
{
        struct subprocess_info *sub_info =
                container_of(work, struct subprocess_info, work);

        if (sub_info->wait & UMH_WAIT_PROC) {
                call_usermodehelper_exec_sync(sub_info);
        } else {
                pid_t pid;
                /*
                 * Use CLONE_PARENT to reparent it to kthreadd; we do not
                 * want to pollute current->children, and we need a parent
                 * that always ignores SIGCHLD to ensure auto-reaping.
                 */
                pid = kernel_thread(call_usermodehelper_exec_async, sub_info,
                                    CLONE_PARENT | SIGCHLD);
                if (pid < 0) {
                        sub_info->retval = pid;
                        umh_complete(sub_info);
                }
        }
}

/*
 * If set, call_usermodehelper_exec() will exit immediately returning -EBUSY
 * (used for preventing user land processes from being created after the user
 * land has been frozen during a system-wide hibernation or suspend operation).
 * Should always be manipulated under umhelper_sem acquired for write.
 */
static enum umh_disable_depth usermodehelper_disabled = UMH_DISABLED;

/* Number of helpers running */
static atomic_t running_helpers = ATOMIC_INIT(0);

/*
 * Wait queue head used by usermodehelper_disable() to wait for all running
 * helpers to finish.
 */
static DECLARE_WAIT_QUEUE_HEAD(running_helpers_waitq);

/*
 * Used by usermodehelper_read_lock_wait() to wait for usermodehelper_disabled
 * to become 'false'.
 */
static DECLARE_WAIT_QUEUE_HEAD(usermodehelper_disabled_waitq);

/*
 * Time to wait for running_helpers to become zero before the setting of
 * usermodehelper_disabled in usermodehelper_disable() fails
 */
#define RUNNING_HELPERS_TIMEOUT (5 * HZ)

int usermodehelper_read_trylock(void)
{
        DEFINE_WAIT(wait);
        int ret = 0;

        down_read(&umhelper_sem);
        for (;;) {
                prepare_to_wait(&usermodehelper_disabled_waitq, &wait,
                                TASK_INTERRUPTIBLE);
                if (!usermodehelper_disabled)
                        break;

                if (usermodehelper_disabled == UMH_DISABLED)
                        ret = -EAGAIN;

                up_read(&umhelper_sem);

                if (ret)
                        break;

                schedule();
                try_to_freeze();

                down_read(&umhelper_sem);
        }
        finish_wait(&usermodehelper_disabled_waitq, &wait);
        return ret;
}
EXPORT_SYMBOL_GPL(usermodehelper_read_trylock);

long usermodehelper_read_lock_wait(long timeout)
{
        DEFINE_WAIT(wait);

        if (timeout < 0)
                return -EINVAL;

        down_read(&umhelper_sem);
        for (;;) {
                prepare_to_wait(&usermodehelper_disabled_waitq, &wait,
                                TASK_UNINTERRUPTIBLE);
                if (!usermodehelper_disabled)
                        break;

                up_read(&umhelper_sem);

                timeout = schedule_timeout(timeout);
                if (!timeout)
                        break;

                down_read(&umhelper_sem);
        }
        finish_wait(&usermodehelper_disabled_waitq, &wait);
        return timeout;
}
EXPORT_SYMBOL_GPL(usermodehelper_read_lock_wait);

void usermodehelper_read_unlock(void)
{
        up_read(&umhelper_sem);
}
EXPORT_SYMBOL_GPL(usermodehelper_read_unlock);

/**
 * __usermodehelper_set_disable_depth - Modify usermodehelper_disabled.
 * @depth: New value to assign to usermodehelper_disabled.
 *
 * Change the value of usermodehelper_disabled (under umhelper_sem locked for
 * writing) and wakeup tasks waiting for it to change.
 */
void __usermodehelper_set_disable_depth(enum umh_disable_depth depth)
{
        down_write(&umhelper_sem);
        usermodehelper_disabled = depth;
        wake_up(&usermodehelper_disabled_waitq);
        up_write(&umhelper_sem);
}

/**
 * __usermodehelper_disable - Prevent new helpers from being started.
 * @depth: New value to assign to usermodehelper_disabled.
 *
 * Set usermodehelper_disabled to @depth and wait for running helpers to exit.
 */
int __usermodehelper_disable(enum umh_disable_depth depth)
{
        long retval;

        if (!depth)
                return -EINVAL;

        down_write(&umhelper_sem);
        usermodehelper_disabled = depth;
        up_write(&umhelper_sem);

        /*
         * From now on call_usermodehelper_exec() won't start any new
         * helpers, so it is sufficient if running_helpers turns out to
         * be zero at one point (it may be increased later, but that
         * doesn't matter).
         */
        retval = wait_event_timeout(running_helpers_waitq,
                                        atomic_read(&running_helpers) == 0,
                                        RUNNING_HELPERS_TIMEOUT);
        if (retval)
                return 0;

        __usermodehelper_set_disable_depth(UMH_ENABLED);
        return -EAGAIN;
}

static void helper_lock(void)
{
        atomic_inc(&running_helpers);
        smp_mb__after_atomic();
}

static void helper_unlock(void)
{
        if (atomic_dec_and_test(&running_helpers))
                wake_up(&running_helpers_waitq);
}

/**
 * call_usermodehelper_setup - prepare to call a usermode helper
 * @path: path to usermode executable
 * @argv: arg vector for process
 * @envp: environment for process
 * @gfp_mask: gfp mask for memory allocation
 * @cleanup: a cleanup function
 * @init: an init function
 * @data: arbitrary context sensitive data
 *
 * Returns either %NULL on allocation failure, or a subprocess_info
 * structure.  This should be passed to call_usermodehelper_exec to
 * exec the process and free the structure.
 *
 * The init function is used to customize the helper process prior to
 * exec.  A non-zero return code causes the process to error out, exit,
 * and return the failure to the calling process
 *
 * The cleanup function is just before ethe subprocess_info is about to
 * be freed.  This can be used for freeing the argv and envp.  The
 * Function must be runnable in either a process context or the
 * context in which call_usermodehelper_exec is called.
 */
struct subprocess_info *call_usermodehelper_setup(const char *path, char **argv,
                char **envp, gfp_t gfp_mask,
                int (*init)(struct subprocess_info *info, struct cred *new),
                void (*cleanup)(struct subprocess_info *info),
                void *data)
{
        struct subprocess_info *sub_info;
        sub_info = kzalloc(sizeof(struct subprocess_info), gfp_mask);
        if (!sub_info)
                goto out;

        INIT_WORK(&sub_info->work, call_usermodehelper_exec_work);

#ifdef CONFIG_STATIC_USERMODEHELPER
        sub_info->path = CONFIG_STATIC_USERMODEHELPER_PATH;
#else
        sub_info->path = path;
#endif
        sub_info->argv = argv;
        sub_info->envp = envp;

        sub_info->cleanup = cleanup;
        sub_info->init = init;
        sub_info->data = data;
  out:
        return sub_info;
}
EXPORT_SYMBOL(call_usermodehelper_setup);

/**
 * call_usermodehelper_exec - start a usermode application
 * @sub_info: information about the subprocessa
 * @wait: wait for the application to finish and return status.
 *        when UMH_NO_WAIT don't wait at all, but you get no useful error back
 *        when the program couldn't be exec'ed. This makes it safe to call
 *        from interrupt context.
 *
 * Runs a user-space application.  The application is started
 * asynchronously if wait is not set, and runs as a child of system workqueues.
 * (ie. it runs with full root capabilities and optimized affinity).
 */
int call_usermodehelper_exec(struct subprocess_info *sub_info, int wait)
{
        DECLARE_COMPLETION_ONSTACK(done);
        int retval = 0;

        if (!sub_info->path) {
                call_usermodehelper_freeinfo(sub_info);
                return -EINVAL;
        }
        helper_lock();
        if (usermodehelper_disabled) {
                retval = -EBUSY;
                goto out;
        }

        /*
         * If there is no binary for us to call, then just return and get out of
         * here.  This allows us to set STATIC_USERMODEHELPER_PATH to "" and
         * disable all call_usermodehelper() calls.
         */
        if (strlen(sub_info->path) == 0)
                goto out;

        /*
         * Set the completion pointer only if there is a waiter.
         * This makes it possible to use umh_complete to free
         * the data structure in case of UMH_NO_WAIT.
         */
        sub_info->complete = (wait == UMH_NO_WAIT) ? NULL : &done;
        sub_info->wait = wait;

        queue_work(system_unbound_wq, &sub_info->work);
        if (wait == UMH_NO_WAIT)        /* task has freed sub_info */
                goto unlock;

        if (wait & UMH_KILLABLE) {
                retval = wait_for_completion_killable(&done);
                if (!retval)
                        goto wait_done;

                /* umh_complete() will see NULL and free sub_info */
                if (xchg(&sub_info->complete, NULL))
                        goto unlock;
                /* fallthrough, umh_complete() was already called */
        }

        wait_for_completion(&done);
wait_done:
        retval = sub_info->retval;
out:
        call_usermodehelper_freeinfo(sub_info);
unlock:
        helper_unlock();
        return retval;
}
EXPORT_SYMBOL(call_usermodehelper_exec);

/**
 * call_usermodehelper() - prepare and start a usermode application
 * @path: path to usermode executable
 * @argv: arg vector for process
 * @envp: environment for process
 * @wait: wait for the application to finish and return status.
 *        when UMH_NO_WAIT don't wait at all, but you get no useful error back
 *        when the program couldn't be exec'ed. This makes it safe to call
 *        from interrupt context.
 *
 * This function is the equivalent to use call_usermodehelper_setup() and
 * call_usermodehelper_exec().
 */
int call_usermodehelper(const char *path, char **argv, char **envp, int wait)
{
        struct subprocess_info *info;
        gfp_t gfp_mask = (wait == UMH_NO_WAIT) ? GFP_ATOMIC : GFP_KERNEL;

        info = call_usermodehelper_setup(path, argv, envp, gfp_mask,
                                         NULL, NULL, NULL);
        if (info == NULL)
                return -ENOMEM;

        return call_usermodehelper_exec(info, wait);
}
EXPORT_SYMBOL(call_usermodehelper);

static int proc_cap_handler(struct ctl_table *table, int write,
                         void __user *buffer, size_t *lenp, loff_t *ppos)
{
        struct ctl_table t;
        unsigned long cap_array[_KERNEL_CAPABILITY_U32S];
        kernel_cap_t new_cap;
        int err, i;

        if (write && (!capable(CAP_SETPCAP) ||
                      !capable(CAP_SYS_MODULE)))
                return -EPERM;

        /*
         * convert from the global kernel_cap_t to the ulong array to print to
         * userspace if this is a read.
         */
        spin_lock(&umh_sysctl_lock);
        for (i = 0; i < _KERNEL_CAPABILITY_U32S; i++)  {
                if (table->data == CAP_BSET)
                        cap_array[i] = usermodehelper_bset.cap[i];
                else if (table->data == CAP_PI)
                        cap_array[i] = usermodehelper_inheritable.cap[i];
                else
                        BUG();
        }
        spin_unlock(&umh_sysctl_lock);

        t = *table;
        t.data = &cap_array;

        /*
         * actually read or write and array of ulongs from userspace.  Remember
         * these are least significant 32 bits first
         */
        err = proc_doulongvec_minmax(&t, write, buffer, lenp, ppos);
        if (err < 0)
                return err;

        /*
         * convert from the sysctl array of ulongs to the kernel_cap_t
         * internal representation
         */
        for (i = 0; i < _KERNEL_CAPABILITY_U32S; i++)
                new_cap.cap[i] = cap_array[i];

        /*
         * Drop everything not in the new_cap (but don't add things)
         */
        if (write) {
                spin_lock(&umh_sysctl_lock);
                if (table->data == CAP_BSET)
                        usermodehelper_bset = cap_intersect(usermodehelper_bset, new_cap);
                if (table->data == CAP_PI)
                        usermodehelper_inheritable = cap_intersect(usermodehelper_inheritable, new_cap);
                spin_unlock(&umh_sysctl_lock);
        }

        return 0;
}

struct ctl_table usermodehelper_table[] = {
        {
                .procname       = "bset",
                .data           = CAP_BSET,
                .maxlen         = _KERNEL_CAPABILITY_U32S * sizeof(unsigned long),
                .mode           = 0600,
                .proc_handler   = proc_cap_handler,
        },
        {
                .procname       = "inheritable",
                .data           = CAP_PI,
                .maxlen         = _KERNEL_CAPABILITY_U32S * sizeof(unsigned long),
                .mode           = 0600,
                .proc_handler   = proc_cap_handler,
        },
        { }
};