arch/um/os-Linux/umid.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
   4  */
   5
   6 #include <stdio.h>
   7 #include <stdlib.h>
   8 #include <dirent.h>
   9 #include <errno.h>
  10 #include <fcntl.h>
  11 #include <signal.h>
  12 #include <string.h>
  13 #include <unistd.h>
  14 #include <sys/stat.h>
  15 #include <init.h>
  16 #include <os.h>
  17
  18 #define UML_DIR "~/.uml/"
  19
  20 #define UMID_LEN 64
  21
  22 /* Changed by set_umid, which is run early in boot */
  23 static char umid[UMID_LEN] = { 0 };
  24
  25 /* Changed by set_uml_dir and make_uml_dir, which are run early in boot */
  26 static char *uml_dir = UML_DIR;
  27
  28 static int __init make_uml_dir(void)
  29 {
  30         char dir[512] = { '\0' };
  31         int len, err;
  32
  33         if (*uml_dir == '~') {
  34                 char *home = getenv("HOME");
  35
  36                 err = -ENOENT;
  37                 if (home == NULL) {
  38                         printk(UM_KERN_ERR
  39                                 "%s: no value in environment for $HOME\n",
  40                                 __func__);
  41                         goto err;
  42                 }
  43                 strlcpy(dir, home, sizeof(dir));
  44                 uml_dir++;
  45         }
  46         strlcat(dir, uml_dir, sizeof(dir));
  47         len = strlen(dir);
  48         if (len > 0 && dir[len - 1] != '/')
  49                 strlcat(dir, "/", sizeof(dir));
  50
  51         err = -ENOMEM;
  52         uml_dir = malloc(strlen(dir) + 1);
  53         if (uml_dir == NULL) {
  54                 printk(UM_KERN_ERR "%s : malloc failed, errno = %d\n",
  55                         __func__, errno);
  56                 goto err;
  57         }
  58         strcpy(uml_dir, dir);
  59
  60         if ((mkdir(uml_dir, 0777) < 0) && (errno != EEXIST)) {
  61                 printk(UM_KERN_ERR "Failed to mkdir '%s': %s\n",
  62                         uml_dir, strerror(errno));
  63                 err = -errno;
  64                 goto err_free;
  65         }
  66         return 0;
  67
  68 err_free:
  69         free(uml_dir);
  70 err:
  71         uml_dir = NULL;
  72         return err;
  73 }
  74
  75 /*
  76  * Unlinks the files contained in @dir and then removes @dir.
  77  * Doesn't handle directory trees, so it's not like rm -rf, but almost such. We
  78  * ignore ENOENT errors for anything (they happen, strangely enough - possibly
  79  * due to races between multiple dying UML threads).
  80  */
  81 static int remove_files_and_dir(char *dir)
  82 {
  83         DIR *directory;
  84         struct dirent *ent;
  85         int len;
  86         char file[256];
  87         int ret;
  88
  89         directory = opendir(dir);
  90         if (directory == NULL) {
  91                 if (errno != ENOENT)
  92                         return -errno;
  93                 else
  94                         return 0;
  95         }
  96
  97         while ((ent = readdir(directory)) != NULL) {
  98                 if (!strcmp(ent->d_name, ".") || !strcmp(ent->d_name, ".."))
  99                         continue;
 100                 len = strlen(dir) + strlen("/") + strlen(ent->d_name) + 1;
 101                 if (len > sizeof(file)) {
 102                         ret = -E2BIG;
 103                         goto out;
 104                 }
 105
 106                 sprintf(file, "%s/%s", dir, ent->d_name);
 107                 if (unlink(file) < 0 && errno != ENOENT) {
 108                         ret = -errno;
 109                         goto out;
 110                 }
 111         }
 112
 113         if (rmdir(dir) < 0 && errno != ENOENT) {
 114                 ret = -errno;
 115                 goto out;
 116         }
 117
 118         ret = 0;
 119 out:
 120         closedir(directory);
 121         return ret;
 122 }
 123
 124 /*
 125  * This says that there isn't already a user of the specified directory even if
 126  * there are errors during the checking.  This is because if these errors
 127  * happen, the directory is unusable by the pre-existing UML, so we might as
 128  * well take it over.  This could happen either by
 129  *      the existing UML somehow corrupting its umid directory
 130  *      something other than UML sticking stuff in the directory
 131  *      this boot racing with a shutdown of the other UML
 132  * In any of these cases, the directory isn't useful for anything else.
 133  *
 134  * Boolean return: 1 if in use, 0 otherwise.
 135  */
 136 static inline int is_umdir_used(char *dir)
 137 {
 138         char pid[sizeof("nnnnnnnnn")], *end, *file;
 139         int dead, fd, p, n, err;
 140         size_t filelen = strlen(dir) + sizeof("/pid") + 1;
 141
 142         file = malloc(filelen);
 143         if (!file)
 144                 return -ENOMEM;
 145
 146         snprintf(file, filelen, "%s/pid", dir);
 147
 148         dead = 0;
 149         fd = open(file, O_RDONLY);
 150         if (fd < 0) {
 151                 fd = -errno;
 152                 if (fd != -ENOENT) {
 153                         printk(UM_KERN_ERR "is_umdir_used : couldn't open pid "
 154                                "file '%s', err = %d\n", file, -fd);
 155                 }
 156                 goto out;
 157         }
 158
 159         err = 0;
 160         n = read(fd, pid, sizeof(pid));
 161         if (n < 0) {
 162                 printk(UM_KERN_ERR "is_umdir_used : couldn't read pid file "
 163                        "'%s', err = %d\n", file, errno);
 164                 goto out_close;
 165         } else if (n == 0) {
 166                 printk(UM_KERN_ERR "is_umdir_used : couldn't read pid file "
 167                        "'%s', 0-byte read\n", file);
 168                 goto out_close;
 169         }
 170
 171         p = strtoul(pid, &end, 0);
 172         if (end == pid) {
 173                 printk(UM_KERN_ERR "is_umdir_used : couldn't parse pid file "
 174                        "'%s', errno = %d\n", file, errno);
 175                 goto out_close;
 176         }
 177
 178         if ((kill(p, 0) == 0) || (errno != ESRCH)) {
 179                 printk(UM_KERN_ERR "umid \"%s\" is already in use by pid %d\n",
 180                        umid, p);
 181                 return 1;
 182         }
 183
 184 out_close:
 185         close(fd);
 186 out:
 187         free(file);
 188         return 0;
 189 }
 190
 191 /*
 192  * Try to remove the directory @dir unless it's in use.
 193  * Precondition: @dir exists.
 194  * Returns 0 for success, < 0 for failure in removal or if the directory is in
 195  * use.
 196  */
 197 static int umdir_take_if_dead(char *dir)
 198 {
 199         int ret;
 200         if (is_umdir_used(dir))
 201                 return -EEXIST;
 202
 203         ret = remove_files_and_dir(dir);
 204         if (ret) {
 205                 printk(UM_KERN_ERR "is_umdir_used - remove_files_and_dir "
 206                        "failed with err = %d\n", ret);
 207         }
 208         return ret;
 209 }
 210
 211 static void __init create_pid_file(void)
 212 {
 213         char pid[sizeof("nnnnnnnnn")], *file;
 214         int fd, n;
 215
 216         n = strlen(uml_dir) + UMID_LEN + sizeof("/pid");
 217         file = malloc(n);
 218         if (!file)
 219                 return;
 220
 221         if (umid_file_name("pid", file, n))
 222                 goto out;
 223
 224         fd = open(file, O_RDWR | O_CREAT | O_EXCL, 0644);
 225         if (fd < 0) {
 226                 printk(UM_KERN_ERR "Open of machine pid file \"%s\" failed: "
 227                        "%s\n", file, strerror(errno));
 228                 goto out;
 229         }
 230
 231         snprintf(pid, sizeof(pid), "%d\n", getpid());
 232         n = write(fd, pid, strlen(pid));
 233         if (n != strlen(pid))
 234                 printk(UM_KERN_ERR "Write of pid file failed - err = %d\n",
 235                        errno);
 236
 237         close(fd);
 238 out:
 239         free(file);
 240 }
 241
 242 int __init set_umid(char *name)
 243 {
 244         if (strlen(name) > UMID_LEN - 1)
 245                 return -E2BIG;
 246
 247         strlcpy(umid, name, sizeof(umid));
 248
 249         return 0;
 250 }
 251
 252 /* Changed in make_umid, which is called during early boot */
 253 static int umid_setup = 0;
 254
 255 static int __init make_umid(void)
 256 {
 257         int fd, err;
 258         char tmp[256];
 259
 260         if (umid_setup)
 261                 return 0;
 262
 263         make_uml_dir();
 264
 265         if (*umid == '\0') {
 266                 strlcpy(tmp, uml_dir, sizeof(tmp));
 267                 strlcat(tmp, "XXXXXX", sizeof(tmp));
 268                 fd = mkstemp(tmp);
 269                 if (fd < 0) {
 270                         printk(UM_KERN_ERR "make_umid - mkstemp(%s) failed: "
 271                                "%s\n", tmp, strerror(errno));
 272                         err = -errno;
 273                         goto err;
 274                 }
 275
 276                 close(fd);
 277
 278                 set_umid(&tmp[strlen(uml_dir)]);
 279
 280                 /*
 281                  * There's a nice tiny little race between this unlink and
 282                  * the mkdir below.  It'd be nice if there were a mkstemp
 283                  * for directories.
 284                  */
 285                 if (unlink(tmp)) {
 286                         err = -errno;
 287                         goto err;
 288                 }
 289         }
 290
 291         snprintf(tmp, sizeof(tmp), "%s%s", uml_dir, umid);
 292         err = mkdir(tmp, 0777);
 293         if (err < 0) {
 294                 err = -errno;
 295                 if (err != -EEXIST)
 296                         goto err;
 297
 298                 if (umdir_take_if_dead(tmp) < 0)
 299                         goto err;
 300
 301                 err = mkdir(tmp, 0777);
 302         }
 303         if (err) {
 304                 err = -errno;
 305                 printk(UM_KERN_ERR "Failed to create '%s' - err = %d\n", umid,
 306                        errno);
 307                 goto err;
 308         }
 309
 310         umid_setup = 1;
 311
 312         create_pid_file();
 313
 314         err = 0;
 315  err:
 316         return err;
 317 }
 318
 319 static int __init make_umid_init(void)
 320 {
 321         if (!make_umid())
 322                 return 0;
 323
 324         /*
 325          * If initializing with the given umid failed, then try again with
 326          * a random one.
 327          */
 328         printk(UM_KERN_ERR "Failed to initialize umid \"%s\", trying with a "
 329                "random umid\n", umid);
 330         *umid = '\0';
 331         make_umid();
 332
 333         return 0;
 334 }
 335
 336 __initcall(make_umid_init);
 337
 338 int __init umid_file_name(char *name, char *buf, int len)
 339 {
 340         int n, err;
 341
 342         err = make_umid();
 343         if (err)
 344                 return err;
 345
 346         n = snprintf(buf, len, "%s%s/%s", uml_dir, umid, name);
 347         if (n >= len) {
 348                 printk(UM_KERN_ERR "umid_file_name : buffer too short\n");
 349                 return -E2BIG;
 350         }
 351
 352         return 0;
 353 }
 354
 355 char *get_umid(void)
 356 {
 357         return umid;
 358 }
 359
 360 static int __init set_uml_dir(char *name, int *add)
 361 {
 362         if (*name == '\0') {
 363                 os_warn("uml_dir can't be an empty string\n");
 364                 return 0;
 365         }
 366
 367         if (name[strlen(name) - 1] == '/') {
 368                 uml_dir = name;
 369                 return 0;
 370         }
 371
 372         uml_dir = malloc(strlen(name) + 2);
 373         if (uml_dir == NULL) {
 374                 os_warn("Failed to malloc uml_dir - error = %d\n", errno);
 375
 376                 /*
 377                  * Return 0 here because do_initcalls doesn't look at
 378                  * the return value.
 379                  */
 380                 return 0;
 381         }
 382         sprintf(uml_dir, "%s/", name);
 383
 384         return 0;
 385 }
 386
 387 __uml_setup("uml_dir=", set_uml_dir,
 388 "uml_dir=<directory>\n"
 389 "    The location to place the pid and umid files.\n\n"
 390 );
 391
 392 static void remove_umid_dir(void)
 393 {
 394         char *dir, err;
 395
 396         dir = malloc(strlen(uml_dir) + UMID_LEN + 1);
 397         if (!dir)
 398                 return;
 399
 400         sprintf(dir, "%s%s", uml_dir, umid);
 401         err = remove_files_and_dir(dir);
 402         if (err)
 403                 os_warn("%s - remove_files_and_dir failed with err = %d\n",
 404                         __func__, err);
 405
 406         free(dir);
 407 }
 408
 409 __uml_exitcall(remove_umid_dir);