// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
 */

#include <stdio.h>
#include <stdlib.h>
#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include <signal.h>
#include <string.h>
#include <unistd.h>
#include <sys/stat.h>
#include <init.h>
#include <os.h>

#define UML_DIR "~/.uml/"

#define UMID_LEN 64

/* Changed by set_umid, which is run early in boot */
static char umid[UMID_LEN] = { 0 };

/* Changed by set_uml_dir and make_uml_dir, which are run early in boot */
static char *uml_dir = UML_DIR;

static int __init make_uml_dir(void)
{
        char dir[512] = { '\0' };
        int len, err;

        if (*uml_dir == '~') {
                char *home = getenv("HOME");

                err = -ENOENT;
                if (home == NULL) {
                        printk(UM_KERN_ERR
                                "%s: no value in environment for $HOME\n",
                                __func__);
                        goto err;
                }
                strlcpy(dir, home, sizeof(dir));
                uml_dir++;
        }
        strlcat(dir, uml_dir, sizeof(dir));
        len = strlen(dir);
        if (len > 0 && dir[len - 1] != '/')
                strlcat(dir, "/", sizeof(dir));

        err = -ENOMEM;
        uml_dir = malloc(strlen(dir) + 1);
        if (uml_dir == NULL) {
                printk(UM_KERN_ERR "%s : malloc failed, errno = %d\n",
                        __func__, errno);
                goto err;
        }
        strcpy(uml_dir, dir);

        if ((mkdir(uml_dir, 0777) < 0) && (errno != EEXIST)) {
                printk(UM_KERN_ERR "Failed to mkdir '%s': %s\n",
                        uml_dir, strerror(errno));
                err = -errno;
                goto err_free;
        }
        return 0;

err_free:
        free(uml_dir);
err:
        uml_dir = NULL;
        return err;
}

/*
 * Unlinks the files contained in @dir and then removes @dir.
 * Doesn't handle directory trees, so it's not like rm -rf, but almost such. We
 * ignore ENOENT errors for anything (they happen, strangely enough - possibly
 * due to races between multiple dying UML threads).
 */
static int remove_files_and_dir(char *dir)
{
        DIR *directory;
        struct dirent *ent;
        int len;
        char file[256];
        int ret;

        directory = opendir(dir);
        if (directory == NULL) {
                if (errno != ENOENT)
                        return -errno;
                else
                        return 0;
        }

        while ((ent = readdir(directory)) != NULL) {
                if (!strcmp(ent->d_name, ".") || !strcmp(ent->d_name, ".."))
                        continue;
                len = strlen(dir) + strlen("/") + strlen(ent->d_name) + 1;
                if (len > sizeof(file)) {
                        ret = -E2BIG;
                        goto out;
                }

                sprintf(file, "%s/%s", dir, ent->d_name);
                if (unlink(file) < 0 && errno != ENOENT) {
                        ret = -errno;
                        goto out;
                }
        }

        if (rmdir(dir) < 0 && errno != ENOENT) {
                ret = -errno;
                goto out;
        }

        ret = 0;
out:
        closedir(directory);
        return ret;
}

/*
 * This says that there isn't already a user of the specified directory even if
 * there are errors during the checking.  This is because if these errors
 * happen, the directory is unusable by the pre-existing UML, so we might as
 * well take it over.  This could happen either by
 *      the existing UML somehow corrupting its umid directory
 *      something other than UML sticking stuff in the directory
 *      this boot racing with a shutdown of the other UML
 * In any of these cases, the directory isn't useful for anything else.
 *
 * Boolean return: 1 if in use, 0 otherwise.
 */
static inline int is_umdir_used(char *dir)
{
        char pid[sizeof("nnnnnnnnn")], *end, *file;
        int dead, fd, p, n, err;
        size_t filelen;

        err = asprintf(&file, "%s/pid", dir);
        if (err < 0)
                return 0;

        filelen = strlen(file);

        n = snprintf(file, filelen, "%s/pid", dir);
        if (n >= filelen) {
                printk(UM_KERN_ERR "is_umdir_used - pid filename too long\n");
                err = -E2BIG;
                goto out;
        }

        dead = 0;
        fd = open(file, O_RDONLY);
        if (fd < 0) {
                fd = -errno;
                if (fd != -ENOENT) {
                        printk(UM_KERN_ERR "is_umdir_used : couldn't open pid "
                               "file '%s', err = %d\n", file, -fd);
                }
                goto out;
        }

        err = 0;
        n = read(fd, pid, sizeof(pid));
        if (n < 0) {
                printk(UM_KERN_ERR "is_umdir_used : couldn't read pid file "
                       "'%s', err = %d\n", file, errno);
                goto out_close;
        } else if (n == 0) {
                printk(UM_KERN_ERR "is_umdir_used : couldn't read pid file "
                       "'%s', 0-byte read\n", file);
                goto out_close;
        }

        p = strtoul(pid, &end, 0);
        if (end == pid) {
                printk(UM_KERN_ERR "is_umdir_used : couldn't parse pid file "
                       "'%s', errno = %d\n", file, errno);
                goto out_close;
        }

        if ((kill(p, 0) == 0) || (errno != ESRCH)) {
                printk(UM_KERN_ERR "umid \"%s\" is already in use by pid %d\n",
                       umid, p);
                return 1;
        }

out_close:
        close(fd);
out:
        free(file);
        return 0;
}

/*
 * Try to remove the directory @dir unless it's in use.
 * Precondition: @dir exists.
 * Returns 0 for success, < 0 for failure in removal or if the directory is in
 * use.
 */
static int umdir_take_if_dead(char *dir)
{
        int ret;
        if (is_umdir_used(dir))
                return -EEXIST;

        ret = remove_files_and_dir(dir);
        if (ret) {
                printk(UM_KERN_ERR "is_umdir_used - remove_files_and_dir "
                       "failed with err = %d\n", ret);
        }
        return ret;
}

static void __init create_pid_file(void)
{
        char pid[sizeof("nnnnnnnnn")], *file;
        int fd, n;

        n = strlen(uml_dir) + UMID_LEN + sizeof("/pid");
        file = malloc(n);
        if (!file)
                return;

        if (umid_file_name("pid", file, n))
                goto out;

        fd = open(file, O_RDWR | O_CREAT | O_EXCL, 0644);
        if (fd < 0) {
                printk(UM_KERN_ERR "Open of machine pid file \"%s\" failed: "
                       "%s\n", file, strerror(errno));
                goto out;
        }

        snprintf(pid, sizeof(pid), "%d\n", getpid());
        n = write(fd, pid, strlen(pid));
        if (n != strlen(pid))
                printk(UM_KERN_ERR "Write of pid file failed - err = %d\n",
                       errno);

        close(fd);
out:
        free(file);
}

int __init set_umid(char *name)
{
        if (strlen(name) > UMID_LEN - 1)
                return -E2BIG;

        strlcpy(umid, name, sizeof(umid));

        return 0;
}

/* Changed in make_umid, which is called during early boot */
static int umid_setup = 0;

static int __init make_umid(void)
{
        int fd, err;
        char tmp[256];

        if (umid_setup)
                return 0;

        make_uml_dir();

        if (*umid == '\0') {
                strlcpy(tmp, uml_dir, sizeof(tmp));
                strlcat(tmp, "XXXXXX", sizeof(tmp));
                fd = mkstemp(tmp);
                if (fd < 0) {
                        printk(UM_KERN_ERR "make_umid - mkstemp(%s) failed: "
                               "%s\n", tmp, strerror(errno));
                        err = -errno;
                        goto err;
                }

                close(fd);

                set_umid(&tmp[strlen(uml_dir)]);

                /*
                 * There's a nice tiny little race between this unlink and
                 * the mkdir below.  It'd be nice if there were a mkstemp
                 * for directories.
                 */
                if (unlink(tmp)) {
                        err = -errno;
                        goto err;
                }
        }

        snprintf(tmp, sizeof(tmp), "%s%s", uml_dir, umid);
        err = mkdir(tmp, 0777);
        if (err < 0) {
                err = -errno;
                if (err != -EEXIST)
                        goto err;

                if (umdir_take_if_dead(tmp) < 0)
                        goto err;

                err = mkdir(tmp, 0777);
        }
        if (err) {
                err = -errno;
                printk(UM_KERN_ERR "Failed to create '%s' - err = %d\n", umid,
                       errno);
                goto err;
        }

        umid_setup = 1;

        create_pid_file();

        err = 0;
 err:
        return err;
}

static int __init make_umid_init(void)
{
        if (!make_umid())
                return 0;

        /*
         * If initializing with the given umid failed, then try again with
         * a random one.
         */
        printk(UM_KERN_ERR "Failed to initialize umid \"%s\", trying with a "
               "random umid\n", umid);
        *umid = '\0';
        make_umid();

        return 0;
}

__initcall(make_umid_init);

int __init umid_file_name(char *name, char *buf, int len)
{
        int n, err;

        err = make_umid();
        if (err)
                return err;

        n = snprintf(buf, len, "%s%s/%s", uml_dir, umid, name);
        if (n >= len) {
                printk(UM_KERN_ERR "umid_file_name : buffer too short\n");
                return -E2BIG;
        }

        return 0;
}

char *get_umid(void)
{
        return umid;
}

static int __init set_uml_dir(char *name, int *add)
{
        if (*name == '\0') {
                os_warn("uml_dir can't be an empty string\n");
                return 0;
        }

        if (name[strlen(name) - 1] == '/') {
                uml_dir = name;
                return 0;
        }

        uml_dir = malloc(strlen(name) + 2);
        if (uml_dir == NULL) {
                os_warn("Failed to malloc uml_dir - error = %d\n", errno);

                /*
                 * Return 0 here because do_initcalls doesn't look at
                 * the return value.
                 */
                return 0;
        }
        sprintf(uml_dir, "%s/", name);

        return 0;
}

__uml_setup("uml_dir=", set_uml_dir,
"uml_dir=<directory>\n"
"    The location to place the pid and umid files.\n\n"
);

static void remove_umid_dir(void)
{
        char *dir, err;

        dir = malloc(strlen(uml_dir) + UMID_LEN + 1);
        if (!dir)
                return;

        sprintf(dir, "%s%s", uml_dir, umid);
        err = remove_files_and_dir(dir);
        if (err)
                os_warn("%s - remove_files_and_dir failed with err = %d\n",
                        __func__, err);

        free(dir);
}

__uml_exitcall(remove_umid_dir);