src/shared/base-filesystem.c

   1 /* SPDX-License-Identifier: LGPL-2.1-or-later */
   2
   3 #include <errno.h>
   4 #include <fcntl.h>
   5 #include <stdbool.h>
   6 #include <stdlib.h>
   7 #include <sys/stat.h>
   8 #include <syslog.h>
   9 #include <unistd.h>
  10
  11 #include "alloc-util.h"
  12 #include "base-filesystem.h"
  13 #include "fd-util.h"
  14 #include "log.h"
  15 #include "macro.h"
  16 #include "nulstr-util.h"
  17 #include "path-util.h"
  18 #include "string-util.h"
  19 #include "umask-util.h"
  20 #include "user-util.h"
  21
  22 typedef struct BaseFilesystem {
  23         const char *dir;      /* directory or symlink to create */
  24         mode_t mode;
  25         const char *target;   /* if non-NULL create as symlink to this target */
  26         const char *exists;   /* conditionalize this entry on existance of this file */
  27         bool ignore_failure;
  28 } BaseFilesystem;
  29
  30 static const BaseFilesystem table[] = {
  31         { "bin",      0, "usr/bin\0",                  NULL },
  32         { "lib",      0, "usr/lib\0",                  NULL },
  33         { "root",  0755, NULL,                         NULL, true },
  34         { "sbin",     0, "usr/sbin\0",                 NULL },
  35         { "usr",   0755, NULL,                         NULL },
  36         { "var",   0755, NULL,                         NULL },
  37         { "etc",   0755, NULL,                         NULL },
  38         { "proc",  0755, NULL,                         NULL, true },
  39         { "sys",   0755, NULL,                         NULL, true },
  40         { "dev",   0755, NULL,                         NULL, true },
  41 #if defined(__i386__) || defined(__x86_64__)
  42         /* Various architecture ABIs define the path to the dynamic loader via the /lib64/ subdirectory of
  43          * the root directory. When booting from an otherwise empty root file system (where only /usr/ has
  44          * been mounted into) it is thus necessary to create a symlink pointing to the right subdirectory of
  45          * /usr/ first — otherwise we couldn't invoke any dynamic binary. Let's detect this case here, and
  46          * create the symlink as needed should it be missing. We prefer doing this consistently with Debian's
  47          * multiarch logic, but support Fedora-style multilib too.*/
  48         { "lib64",    0, "usr/lib/x86_64-linux-gnu\0"
  49                          "usr/lib64\0",                "ld-linux-x86-64.so.2" },
  50 #else
  51         /* gcc doesn't allow pragma to be used within constructs, hence log about this separately below */
  52 #  define WARN_LIB64 1
  53 #endif
  54 };
  55
  56 #ifdef WARN_LIB64
  57 #pragma message "If your architecture knows a /lib64/ or /lib32/ directory, please add an entry creating it here."
  58         /* And if your architecture doesn't know these directories, make sure to add ifdeffery here to
  59          * suppress this pragma message. */
  60 #endif
  61
  62 int base_filesystem_create(const char *root, uid_t uid, gid_t gid) {
  63         _cleanup_close_ int fd = -1;
  64         int r;
  65
  66         fd = open(root, O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC|O_NOFOLLOW);
  67         if (fd < 0)
  68                 return log_error_errno(errno, "Failed to open root file system: %m");
  69
  70         for (size_t i = 0; i < ELEMENTSOF(table); i++) {
  71                 if (faccessat(fd, table[i].dir, F_OK, AT_SYMLINK_NOFOLLOW) >= 0)
  72                         continue;
  73
  74                 if (table[i].target) {
  75                         const char *target = NULL, *s;
  76
  77                         /* check if one of the targets exists */
  78                         NULSTR_FOREACH(s, table[i].target) {
  79                                 if (faccessat(fd, s, F_OK, AT_SYMLINK_NOFOLLOW) < 0)
  80                                         continue;
  81
  82                                 /* check if a specific file exists at the target path */
  83                                 if (table[i].exists) {
  84                                         _cleanup_free_ char *p = NULL;
  85
  86                                         p = path_join(s, table[i].exists);
  87                                         if (!p)
  88                                                 return log_oom();
  89
  90                                         if (faccessat(fd, p, F_OK, AT_SYMLINK_NOFOLLOW) < 0)
  91                                                 continue;
  92                                 }
  93
  94                                 target = s;
  95                                 break;
  96                         }
  97
  98                         if (!target)
  99                                 continue;
 100
 101                         if (symlinkat(target, fd, table[i].dir) < 0) {
 102                                 log_full_errno(IN_SET(errno, EEXIST, EROFS) || table[i].ignore_failure ? LOG_DEBUG : LOG_ERR, errno,
 103                                                "Failed to create symlink at %s/%s: %m", root, table[i].dir);
 104
 105                                 if (IN_SET(errno, EEXIST, EROFS) || table[i].ignore_failure)
 106                                         continue;
 107
 108                                 return -errno;
 109                         }
 110
 111                         if (uid_is_valid(uid) || gid_is_valid(gid))
 112                                 if (fchownat(fd, table[i].dir, uid, gid, AT_SYMLINK_NOFOLLOW) < 0)
 113                                         return log_error_errno(errno, "Failed to chown symlink at %s/%s: %m", root, table[i].dir);
 114
 115                         continue;
 116                 }
 117
 118                 RUN_WITH_UMASK(0000)
 119                         r = mkdirat(fd, table[i].dir, table[i].mode);
 120                 if (r < 0) {
 121                         log_full_errno(IN_SET(errno, EEXIST, EROFS) || table[i].ignore_failure ? LOG_DEBUG : LOG_ERR, errno,
 122                                        "Failed to create directory at %s/%s: %m", root, table[i].dir);
 123
 124                         if (IN_SET(errno, EEXIST, EROFS) || table[i].ignore_failure)
 125                                 continue;
 126
 127                         return -errno;
 128                 }
 129
 130                 if (uid != UID_INVALID || gid != UID_INVALID)
 131                         if (fchownat(fd, table[i].dir, uid, gid, AT_SYMLINK_NOFOLLOW) < 0)
 132                                 return log_error_errno(errno, "Failed to chown directory at %s/%s: %m", root, table[i].dir);
 133         }
 134
 135         return 0;
 136 }