um/os-Linux/umid.c

0001 // SPDX-License-Identifier: GPL-2.0
0002 /*
0003  * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
0004  */
0005
0006 #include <stdio.h>
0007 #include <stdlib.h>
0008 #include <dirent.h>
0009 #include <errno.h>
0010 #include <fcntl.h>
0011 #include <signal.h>
0012 #include <string.h>
0013 #include <unistd.h>
0014 #include <sys/stat.h>
0015 #include <init.h>
0016 #include <os.h>
0017
0018 #define UML_DIR "~/.uml/"
0019
0020 #define UMID_LEN 64
0021
0022 /* Changed by set_umid, which is run early in boot */
0023 static char umid[UMID_LEN] = { 0 };
0024
0025 /* Changed by set_uml_dir and make_uml_dir, which are run early in boot */
0026 static char *uml_dir = UML_DIR;
0027
0028 static int __init make_uml_dir(void)
0029 {
0030     char dir[512] = { '\0' };
0031     int len, err;
0032
0033     if (*uml_dir == '~') {
0034         char *home = getenv("HOME");
0035
0036         err = -ENOENT;
0037         if (home == NULL) {
0038             printk(UM_KERN_ERR
0039                 "%s: no value in environment for $HOME\n",
0040                 __func__);
0041             goto err;
0042         }
0043         strlcpy(dir, home, sizeof(dir));
0044         uml_dir++;
0045     }
0046     strlcat(dir, uml_dir, sizeof(dir));
0047     len = strlen(dir);
0048     if (len > 0 && dir[len - 1] != '/')
0049         strlcat(dir, "/", sizeof(dir));
0050
0051     err = -ENOMEM;
0052     uml_dir = malloc(strlen(dir) + 1);
0053     if (uml_dir == NULL) {
0054         printk(UM_KERN_ERR "%s : malloc failed, errno = %d\n",
0055             __func__, errno);
0056         goto err;
0057     }
0058     strcpy(uml_dir, dir);
0059
0060     if ((mkdir(uml_dir, 0777) < 0) && (errno != EEXIST)) {
0061         printk(UM_KERN_ERR "Failed to mkdir '%s': %s\n",
0062             uml_dir, strerror(errno));
0063         err = -errno;
0064         goto err_free;
0065     }
0066     return 0;
0067
0068 err_free:
0069     free(uml_dir);
0070 err:
0071     uml_dir = NULL;
0072     return err;
0073 }
0074
0075 /*
0076  * Unlinks the files contained in @dir and then removes @dir.
0077  * Doesn't handle directory trees, so it's not like rm -rf, but almost such. We
0078  * ignore ENOENT errors for anything (they happen, strangely enough - possibly
0079  * due to races between multiple dying UML threads).
0080  */
0081 static int remove_files_and_dir(char *dir)
0082 {
0083     DIR *directory;
0084     struct dirent *ent;
0085     int len;
0086     char file[256];
0087     int ret;
0088
0089     directory = opendir(dir);
0090     if (directory == NULL) {
0091         if (errno != ENOENT)
0092             return -errno;
0093         else
0094             return 0;
0095     }
0096
0097     while ((ent = readdir(directory)) != NULL) {
0098         if (!strcmp(ent->d_name, ".") || !strcmp(ent->d_name, ".."))
0099             continue;
0100         len = strlen(dir) + strlen("/") + strlen(ent->d_name) + 1;
0101         if (len > sizeof(file)) {
0102             ret = -E2BIG;
0103             goto out;
0104         }
0105
0106         sprintf(file, "%s/%s", dir, ent->d_name);
0107         if (unlink(file) < 0 && errno != ENOENT) {
0108             ret = -errno;
0109             goto out;
0110         }
0111     }
0112
0113     if (rmdir(dir) < 0 && errno != ENOENT) {
0114         ret = -errno;
0115         goto out;
0116     }
0117
0118     ret = 0;
0119 out:
0120     closedir(directory);
0121     return ret;
0122 }
0123
0124 /*
0125  * This says that there isn't already a user of the specified directory even if
0126  * there are errors during the checking.  This is because if these errors
0127  * happen, the directory is unusable by the pre-existing UML, so we might as
0128  * well take it over.  This could happen either by
0129  *  the existing UML somehow corrupting its umid directory
0130  *  something other than UML sticking stuff in the directory
0131  *  this boot racing with a shutdown of the other UML
0132  * In any of these cases, the directory isn't useful for anything else.
0133  *
0134  * Boolean return: 1 if in use, 0 otherwise.
0135  */
0136 static inline int is_umdir_used(char *dir)
0137 {
0138     char pid[sizeof("nnnnnnnnn")], *end, *file;
0139     int fd, p, n, err;
0140     size_t filelen = strlen(dir) + sizeof("/pid") + 1;
0141
0142     file = malloc(filelen);
0143     if (!file)
0144         return -ENOMEM;
0145
0146     snprintf(file, filelen, "%s/pid", dir);
0147
0148     fd = open(file, O_RDONLY);
0149     if (fd < 0) {
0150         fd = -errno;
0151         if (fd != -ENOENT) {
0152             printk(UM_KERN_ERR "is_umdir_used : couldn't open pid "
0153                    "file '%s', err = %d\n", file, -fd);
0154         }
0155         goto out;
0156     }
0157
0158     err = 0;
0159     n = read(fd, pid, sizeof(pid));
0160     if (n < 0) {
0161         printk(UM_KERN_ERR "is_umdir_used : couldn't read pid file "
0162                "'%s', err = %d\n", file, errno);
0163         goto out_close;
0164     } else if (n == 0) {
0165         printk(UM_KERN_ERR "is_umdir_used : couldn't read pid file "
0166                "'%s', 0-byte read\n", file);
0167         goto out_close;
0168     }
0169
0170     p = strtoul(pid, &end, 0);
0171     if (end == pid) {
0172         printk(UM_KERN_ERR "is_umdir_used : couldn't parse pid file "
0173                "'%s', errno = %d\n", file, errno);
0174         goto out_close;
0175     }
0176
0177     if ((kill(p, 0) == 0) || (errno != ESRCH)) {
0178         printk(UM_KERN_ERR "umid \"%s\" is already in use by pid %d\n",
0179                umid, p);
0180         return 1;
0181     }
0182
0183 out_close:
0184     close(fd);
0185 out:
0186     free(file);
0187     return 0;
0188 }
0189
0190 /*
0191  * Try to remove the directory @dir unless it's in use.
0192  * Precondition: @dir exists.
0193  * Returns 0 for success, < 0 for failure in removal or if the directory is in
0194  * use.
0195  */
0196 static int umdir_take_if_dead(char *dir)
0197 {
0198     int ret;
0199     if (is_umdir_used(dir))
0200         return -EEXIST;
0201
0202     ret = remove_files_and_dir(dir);
0203     if (ret) {
0204         printk(UM_KERN_ERR "is_umdir_used - remove_files_and_dir "
0205                "failed with err = %d\n", ret);
0206     }
0207     return ret;
0208 }
0209
0210 static void __init create_pid_file(void)
0211 {
0212     char pid[sizeof("nnnnnnnnn")], *file;
0213     int fd, n;
0214
0215     n = strlen(uml_dir) + UMID_LEN + sizeof("/pid");
0216     file = malloc(n);
0217     if (!file)
0218         return;
0219
0220     if (umid_file_name("pid", file, n))
0221         goto out;
0222
0223     fd = open(file, O_RDWR | O_CREAT | O_EXCL, 0644);
0224     if (fd < 0) {
0225         printk(UM_KERN_ERR "Open of machine pid file \"%s\" failed: "
0226                "%s\n", file, strerror(errno));
0227         goto out;
0228     }
0229
0230     snprintf(pid, sizeof(pid), "%d\n", getpid());
0231     n = write(fd, pid, strlen(pid));
0232     if (n != strlen(pid))
0233         printk(UM_KERN_ERR "Write of pid file failed - err = %d\n",
0234                errno);
0235
0236     close(fd);
0237 out:
0238     free(file);
0239 }
0240
0241 int __init set_umid(char *name)
0242 {
0243     if (strlen(name) > UMID_LEN - 1)
0244         return -E2BIG;
0245
0246     strlcpy(umid, name, sizeof(umid));
0247
0248     return 0;
0249 }
0250
0251 /* Changed in make_umid, which is called during early boot */
0252 static int umid_setup = 0;
0253
0254 static int __init make_umid(void)
0255 {
0256     int fd, err;
0257     char tmp[256];
0258
0259     if (umid_setup)
0260         return 0;
0261
0262     make_uml_dir();
0263
0264     if (*umid == '\0') {
0265         strlcpy(tmp, uml_dir, sizeof(tmp));
0266         strlcat(tmp, "XXXXXX", sizeof(tmp));
0267         fd = mkstemp(tmp);
0268         if (fd < 0) {
0269             printk(UM_KERN_ERR "make_umid - mkstemp(%s) failed: "
0270                    "%s\n", tmp, strerror(errno));
0271             err = -errno;
0272             goto err;
0273         }
0274
0275         close(fd);
0276
0277         set_umid(&tmp[strlen(uml_dir)]);
0278
0279         /*
0280          * There's a nice tiny little race between this unlink and
0281          * the mkdir below.  It'd be nice if there were a mkstemp
0282          * for directories.
0283          */
0284         if (unlink(tmp)) {
0285             err = -errno;
0286             goto err;
0287         }
0288     }
0289
0290     snprintf(tmp, sizeof(tmp), "%s%s", uml_dir, umid);
0291     err = mkdir(tmp, 0777);
0292     if (err < 0) {
0293         err = -errno;
0294         if (err != -EEXIST)
0295             goto err;
0296
0297         if (umdir_take_if_dead(tmp) < 0)
0298             goto err;
0299
0300         err = mkdir(tmp, 0777);
0301     }
0302     if (err) {
0303         err = -errno;
0304         printk(UM_KERN_ERR "Failed to create '%s' - err = %d\n", umid,
0305                errno);
0306         goto err;
0307     }
0308
0309     umid_setup = 1;
0310
0311     create_pid_file();
0312
0313     err = 0;
0314  err:
0315     return err;
0316 }
0317
0318 static int __init make_umid_init(void)
0319 {
0320     if (!make_umid())
0321         return 0;
0322
0323     /*
0324      * If initializing with the given umid failed, then try again with
0325      * a random one.
0326      */
0327     printk(UM_KERN_ERR "Failed to initialize umid \"%s\", trying with a "
0328            "random umid\n", umid);
0329     *umid = '\0';
0330     make_umid();
0331
0332     return 0;
0333 }
0334
0335 __initcall(make_umid_init);
0336
0337 int __init umid_file_name(char *name, char *buf, int len)
0338 {
0339     int n, err;
0340
0341     err = make_umid();
0342     if (err)
0343         return err;
0344
0345     n = snprintf(buf, len, "%s%s/%s", uml_dir, umid, name);
0346     if (n >= len) {
0347         printk(UM_KERN_ERR "umid_file_name : buffer too short\n");
0348         return -E2BIG;
0349     }
0350
0351     return 0;
0352 }
0353
0354 char *get_umid(void)
0355 {
0356     return umid;
0357 }
0358
0359 static int __init set_uml_dir(char *name, int *add)
0360 {
0361     if (*name == '\0') {
0362         os_warn("uml_dir can't be an empty string\n");
0363         return 0;
0364     }
0365
0366     if (name[strlen(name) - 1] == '/') {
0367         uml_dir = name;
0368         return 0;
0369     }
0370
0371     uml_dir = malloc(strlen(name) + 2);
0372     if (uml_dir == NULL) {
0373         os_warn("Failed to malloc uml_dir - error = %d\n", errno);
0374
0375         /*
0376          * Return 0 here because do_initcalls doesn't look at
0377          * the return value.
0378          */
0379         return 0;
0380     }
0381     sprintf(uml_dir, "%s/", name);
0382
0383     return 0;
0384 }
0385
0386 __uml_setup("uml_dir=", set_uml_dir,
0387 "uml_dir=<directory>\n"
0388 "    The location to place the pid and umid files.\n\n"
0389 );
0390
0391 static void remove_umid_dir(void)
0392 {
0393     char *dir, err;
0394
0395     dir = malloc(strlen(uml_dir) + UMID_LEN + 1);
0396     if (!dir)
0397         return;
0398
0399     sprintf(dir, "%s%s", uml_dir, umid);
0400     err = remove_files_and_dir(dir);
0401     if (err)
0402         os_warn("%s - remove_files_and_dir failed with err = %d\n",
0403             __func__, err);
0404
0405     free(dir);
0406 }
0407
0408 __uml_exitcall(remove_umid_dir);