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 "architecture.h"
  13 #include "base-filesystem.h"
  14 #include "errno-util.h"
  15 #include "fd-util.h"
  16 #include "log.h"
  17 #include "macro.h"
  18 #include "nulstr-util.h"
  19 #include "path-util.h"
  20 #include "string-util.h"
  21 #include "umask-util.h"
  22 #include "user-util.h"
  23
  24 typedef struct BaseFilesystem {
  25         const char *dir;      /* directory or symlink to create */
  26         mode_t mode;
  27         const char *target;   /* if non-NULL create as symlink to this target */
  28         const char *exists;   /* conditionalize this entry on existence of this file */
  29         bool ignore_failure;
  30 } BaseFilesystem;
  31
  32 static const BaseFilesystem table[] = {
  33         { "bin",      0, "usr/bin\0",                  NULL },
  34         { "lib",      0, "usr/lib\0",                  NULL },
  35         { "root",  0750, NULL,                         NULL, true },
  36         { "sbin",     0, "usr/sbin\0",                 NULL },
  37         { "usr",   0755, NULL,                         NULL },
  38         { "var",   0755, NULL,                         NULL },
  39         { "etc",   0755, NULL,                         NULL },
  40         { "proc",  0555, NULL,                         NULL, true },
  41         { "sys",   0555, NULL,                         NULL, true },
  42         { "dev",   0555, NULL,                         NULL, true },
  43         { "run",   0555, NULL,                         NULL, true },
  44         /* We don't add /tmp/ here for now (even though it's necessary for regular operation), because we
  45          * want to support both cases where /tmp/ is a mount of its own (in which case we probably should set
  46          * the mode to 1555, to indicate that no one should write to it, not even root) and when it's part of
  47          * the rootfs (in which case we should set mode 1777), and we simply don't know what's right. */
  48
  49         /* Various architecture ABIs define the path to the dynamic loader via the /lib64/ subdirectory of
  50          * the root directory. When booting from an otherwise empty root file system (where only /usr/ has
  51          * been mounted into) it is thus necessary to create a symlink pointing to the right subdirectory of
  52          * /usr/ first — otherwise we couldn't invoke any dynamic binary. Let's detect this case here, and
  53          * create the symlink as needed should it be missing. We prefer doing this consistently with Debian's
  54          * multiarch logic, but support Fedora-style and Arch-style multilib too. */
  55 #if defined(__aarch64__)
  56         /* aarch64 ELF ABI actually says dynamic loader is in /lib/, but Fedora puts it in /lib64/ anyway and
  57          * just symlinks /lib/ld-linux-aarch64.so.1 to ../lib64/ld-linux-aarch64.so.1. For this to work
  58          * correctly, /lib64/ must be symlinked to /usr/lib64/. */
  59         { "lib64",    0, "usr/lib/"LIB_ARCH_TUPLE"\0"
  60                          "usr/lib64\0"
  61                          "usr/lib\0",                "ld-linux-aarch64.so.1" },
  62 #  define KNOW_LIB64_DIRS 1
  63 #elif defined(__alpha__)
  64 #elif defined(__arc__) || defined(__tilegx__)
  65 #elif defined(__arm__)
  66         /* No /lib64 on arm. The linker is /lib/ld-linux-armhf.so.3. */
  67 #  define KNOW_LIB64_DIRS 1
  68 #elif defined(__i386__) || defined(__x86_64__)
  69         { "lib64",    0, "usr/lib/"LIB_ARCH_TUPLE"\0"
  70                          "usr/lib64\0"
  71                          "usr/lib\0",                "ld-linux-x86-64.so.2" },
  72 #  define KNOW_LIB64_DIRS 1
  73 #elif defined(__ia64__)
  74 #elif defined(__loongarch_lp64)
  75 #  define KNOW_LIB64_DIRS 1
  76 #  if defined(__loongarch_double_float)
  77         { "lib64",    0, "usr/lib/"LIB_ARCH_TUPLE"\0"
  78                          "usr/lib64\0"
  79                          "usr/lib\0",                "ld-linux-loongarch-lp64d.so.1" },
  80 #  elif defined(__loongarch_single_float)
  81         { "lib64",    0, "usr/lib/"LIB_ARCH_TUPLE"\0"
  82                          "usr/lib64\0"
  83                          "usr/lib\0",                "ld-linux-loongarch-lp64f.so.1" },
  84 #  elif defined(__loongarch_soft_float)
  85         { "lib64",    0, "usr/lib/"LIB_ARCH_TUPLE"\0"
  86                          "usr/lib64\0"
  87                          "usr/lib\0",                "ld-linux-loongarch-lp64s.so.1" },
  88 #  else
  89 #    error "Unknown LoongArch ABI"
  90 #  endif
  91 #elif defined(__m68k__)
  92         /* No link needed. */
  93 #  define KNOW_LIB64_DIRS 1
  94 #elif defined(_MIPS_SIM)
  95 #  if _MIPS_SIM == _MIPS_SIM_ABI32
  96 #  elif _MIPS_SIM == _MIPS_SIM_NABI32
  97 #  elif _MIPS_SIM == _MIPS_SIM_ABI64
  98 #  else
  99 #    error "Unknown MIPS ABI"
 100 #  endif
 101 #elif defined(__powerpc__)
 102 #  if defined(__PPC64__) && __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
 103         { "lib64",    0, "usr/lib/"LIB_ARCH_TUPLE"\0"
 104                          "usr/lib64\0"
 105                          "usr/lib\0",                "ld64.so.2" },
 106 #    define KNOW_LIB64_DIRS 1
 107 #  elif defined(__powerpc64__) && __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
 108         /* powerpc64-linux-gnu */
 109 #  else
 110         /* powerpc-linux-gnu */
 111 #  endif
 112 #elif defined(__riscv)
 113 #  if __riscv_xlen == 32
 114 #  elif __riscv_xlen == 64
 115         /* Same situation as for aarch64 */
 116         { "lib64",    0, "usr/lib/"LIB_ARCH_TUPLE"\0"
 117                          "usr/lib64\0"
 118                          "usr/lib\0",                "ld-linux-riscv64-lp64d.so.1" },
 119 #    define KNOW_LIB64_DIRS 1
 120 #  else
 121 #    error "Unknown RISC-V ABI"
 122 #  endif
 123 #elif defined(__s390x__)
 124         { "lib64",    0, "usr/lib/"LIB_ARCH_TUPLE"\0"
 125                          "usr/lib64\0"
 126                          "usr/lib\0",                "ld-lsb-s390x.so.3" },
 127 #    define KNOW_LIB64_DIRS 1
 128 #elif defined(__s390__)
 129         /* s390-linux-gnu */
 130 #elif defined(__sparc__)
 131 #endif
 132         /* gcc doesn't allow pragma to be used within constructs, hence log about this separately below */
 133 };
 134
 135 #ifndef KNOW_LIB64_DIRS
 136 #  pragma message "Please add an entry above specifying whether your architecture uses /lib64/, /lib32/, or no such links."
 137 #endif
 138
 139 int base_filesystem_create_fd(int fd, const char *root, uid_t uid, gid_t gid) {
 140         int r;
 141
 142         assert(fd >= 0);
 143         assert(root);
 144
 145         /* The "root" parameter is decoration only – it's only used as part of log messages */
 146
 147         for (size_t i = 0; i < ELEMENTSOF(table); i++) {
 148                 if (faccessat(fd, table[i].dir, F_OK, AT_SYMLINK_NOFOLLOW) >= 0)
 149                         continue;
 150
 151                 if (table[i].target) { /* Create as symlink? */
 152                         const char *target = NULL;
 153
 154                         /* check if one of the targets exists */
 155                         NULSTR_FOREACH(s, table[i].target) {
 156                                 if (faccessat(fd, s, F_OK, AT_SYMLINK_NOFOLLOW) < 0)
 157                                         continue;
 158
 159                                 /* check if a specific file exists at the target path */
 160                                 if (table[i].exists) {
 161                                         _cleanup_free_ char *p = NULL;
 162
 163                                         p = path_join(s, table[i].exists);
 164                                         if (!p)
 165                                                 return log_oom();
 166
 167                                         if (faccessat(fd, p, F_OK, AT_SYMLINK_NOFOLLOW) < 0)
 168                                                 continue;
 169                                 }
 170
 171                                 target = s;
 172                                 break;
 173                         }
 174
 175                         if (!target)
 176                                 continue;
 177
 178                         r = RET_NERRNO(symlinkat(target, fd, table[i].dir));
 179                 } else {
 180                         /* Create as directory. */
 181                         WITH_UMASK(0000)
 182                                 r = RET_NERRNO(mkdirat(fd, table[i].dir, table[i].mode));
 183                 }
 184                 if (r < 0) {
 185                         bool ignore = IN_SET(r, -EEXIST, -EROFS) || table[i].ignore_failure;
 186                         log_full_errno(ignore ? LOG_DEBUG : LOG_ERR, r,
 187                                        "Failed to create %s/%s: %m", root, table[i].dir);
 188                         if (ignore)
 189                                 continue;
 190
 191                         return r;
 192                 }
 193
 194                 if (uid_is_valid(uid) || gid_is_valid(gid))
 195                         if (fchownat(fd, table[i].dir, uid, gid, AT_SYMLINK_NOFOLLOW) < 0)
 196                                 return log_error_errno(errno, "Failed to chown %s/%s: %m", root, table[i].dir);
 197         }
 198
 199         return 0;
 200 }
 201
 202 int base_filesystem_create(const char *root, uid_t uid, gid_t gid) {
 203         _cleanup_close_ int fd = -EBADF;
 204
 205         fd = open(ASSERT_PTR(root), O_DIRECTORY|O_CLOEXEC);
 206         if (fd < 0)
 207                 return log_error_errno(errno, "Failed to open root file system: %m");
 208
 209         return base_filesystem_create_fd(fd, root, uid, gid);
 210 }