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
  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 #if defined(__aarch64__)
  49         /* aarch64 ELF ABI actually says dynamic loader is in /lib/, but Fedora puts it in /lib64/ anyway and
  50          * just symlinks /lib/ld-linux-aarch64.so.1 to ../lib64/ld-linux-aarch64.so.1. For this to work
  51          * correctly, /lib64/ must be symlinked to /usr/lib64/. */
  52         { "lib64",    0, "usr/lib/aarch64-linux-gnu\0"
  53                          "usr/lib64\0",                "ld-linux-aarch64.so.1" },
  54 #  define KNOW_LIB64_DIRS 1
  55 #elif defined(__alpha__)
  56 #elif defined(__arc__) || defined(__tilegx__)
  57 #elif defined(__arm__)
  58 #elif defined(__i386__) || defined(__x86_64__)
  59         { "lib64",    0, "usr/lib/x86_64-linux-gnu\0"
  60                          "usr/lib64\0",                "ld-linux-x86-64.so.2" },
  61 #  define KNOW_LIB64_DIRS 1
  62 #elif defined(__ia64__)
  63 #elif defined(__m68k__)
  64 #elif defined(_MIPS_SIM)
  65 #  if _MIPS_SIM == _MIPS_SIM_ABI32
  66 #  elif _MIPS_SIM == _MIPS_SIM_NABI32
  67 #  elif _MIPS_SIM == _MIPS_SIM_ABI64
  68 #  else
  69 #    error "Unknown MIPS ABI"
  70 #  endif
  71 #elif defined(__powerpc__)
  72 #elif defined(__riscv)
  73 #  if __riscv_xlen == 32
  74 #  elif __riscv_xlen == 64
  75 #  else
  76 #    error "Unknown RISC-V ABI"
  77 #  endif
  78 #elif defined(__s390__)
  79 #elif defined(__s390x__)
  80 #elif defined(__sparc__)
  81 #endif
  82         /* gcc doesn't allow pragma to be used within constructs, hence log about this separately below */
  83 };
  84
  85 #ifndef KNOW_LIB64_DIRS
  86 #  pragma message "Please add an entry above specifying whether your architecture uses /lib64/, /lib32/, or no such links."
  87 #endif
  88
  89 int base_filesystem_create(const char *root, uid_t uid, gid_t gid) {
  90         _cleanup_close_ int fd = -1;
  91         int r;
  92
  93         fd = open(root, O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC|O_NOFOLLOW);
  94         if (fd < 0)
  95                 return log_error_errno(errno, "Failed to open root file system: %m");
  96
  97         for (size_t i = 0; i < ELEMENTSOF(table); i++) {
  98                 if (faccessat(fd, table[i].dir, F_OK, AT_SYMLINK_NOFOLLOW) >= 0)
  99                         continue;
 100
 101                 if (table[i].target) {
 102                         const char *target = NULL, *s;
 103
 104                         /* check if one of the targets exists */
 105                         NULSTR_FOREACH(s, table[i].target) {
 106                                 if (faccessat(fd, s, F_OK, AT_SYMLINK_NOFOLLOW) < 0)
 107                                         continue;
 108
 109                                 /* check if a specific file exists at the target path */
 110                                 if (table[i].exists) {
 111                                         _cleanup_free_ char *p = NULL;
 112
 113                                         p = path_join(s, table[i].exists);
 114                                         if (!p)
 115                                                 return log_oom();
 116
 117                                         if (faccessat(fd, p, F_OK, AT_SYMLINK_NOFOLLOW) < 0)
 118                                                 continue;
 119                                 }
 120
 121                                 target = s;
 122                                 break;
 123                         }
 124
 125                         if (!target)
 126                                 continue;
 127
 128                         if (symlinkat(target, fd, table[i].dir) < 0) {
 129                                 log_full_errno(IN_SET(errno, EEXIST, EROFS) || table[i].ignore_failure ? LOG_DEBUG : LOG_ERR, errno,
 130                                                "Failed to create symlink at %s/%s: %m", root, table[i].dir);
 131
 132                                 if (IN_SET(errno, EEXIST, EROFS) || table[i].ignore_failure)
 133                                         continue;
 134
 135                                 return -errno;
 136                         }
 137
 138                         if (uid_is_valid(uid) || gid_is_valid(gid))
 139                                 if (fchownat(fd, table[i].dir, uid, gid, AT_SYMLINK_NOFOLLOW) < 0)
 140                                         return log_error_errno(errno, "Failed to chown symlink at %s/%s: %m", root, table[i].dir);
 141
 142                         continue;
 143                 }
 144
 145                 RUN_WITH_UMASK(0000)
 146                         r = mkdirat(fd, table[i].dir, table[i].mode);
 147                 if (r < 0) {
 148                         log_full_errno(IN_SET(errno, EEXIST, EROFS) || table[i].ignore_failure ? LOG_DEBUG : LOG_ERR, errno,
 149                                        "Failed to create directory at %s/%s: %m", root, table[i].dir);
 150
 151                         if (IN_SET(errno, EEXIST, EROFS) || table[i].ignore_failure)
 152                                 continue;
 153
 154                         return -errno;
 155                 }
 156
 157                 if (uid != UID_INVALID || gid != UID_INVALID)
 158                         if (fchownat(fd, table[i].dir, uid, gid, AT_SYMLINK_NOFOLLOW) < 0)
 159                                 return log_error_errno(errno, "Failed to chown directory at %s/%s: %m", root, table[i].dir);
 160         }
 161
 162         return 0;
 163 }