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8aefedce147bfc99cf96090e3bd7f4d2c6468fd7
systemd/src/shared/base-filesystem.c
Lennart Poettering 8aefedce14 base-filesystem: add new helper base_filesystem_create_fd() that operates on an fd, instead of a path 
This also changes the open flags from
O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC|O_NOFOLLOW to
O_DIRECTORY|O_CLOEXEC. O_RDONLY is redundant, since O_RDONLY is zero
anyway, and O_DIRECTORY pins the acces mode enough: it doesn't allow
read()/write() anyway when specified. O_NONBLOCK is also pointless given
that O_DIRECTORY is specified, it has no meaning on directories. (It is
useful if we don't know much about the inode we are opening, and could
be a device node or fifo, but the O_DIRECTORY excludes that case.)

O_NOFOLLOW is dropped since there's really no point in blocking out the
initial entrypoint being a symlink. Once we pinned the the root of the
tree it might make sense to restrict symlink use below it, but for the
entrypoint itself it doesn't matter.
2023-05-03 17:55:55 +02:00

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/* SPDX-License-Identifier: LGPL-2.1-or-later */
#include <errno.h>
#include <fcntl.h>
#include <stdbool.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <syslog.h>
#include <unistd.h>
#include "alloc-util.h"
#include "architecture.h"
#include "base-filesystem.h"
#include "fd-util.h"
#include "log.h"
#include "macro.h"
#include "nulstr-util.h"
#include "path-util.h"
#include "string-util.h"
#include "umask-util.h"
#include "user-util.h"
typedef struct BaseFilesystem {
const char *dir; /* directory or symlink to create */
mode_t mode;
const char *target; /* if non-NULL create as symlink to this target */
const char *exists; /* conditionalize this entry on existence of this file */
bool ignore_failure;
} BaseFilesystem;
static const BaseFilesystem table[] = {
{ "bin", 0, "usr/bin\0", NULL },
{ "lib", 0, "usr/lib\0", NULL },
{ "root", 0750, NULL, NULL, true },
{ "sbin", 0, "usr/sbin\0", NULL },
{ "usr", 0755, NULL, NULL },
{ "var", 0755, NULL, NULL },
{ "etc", 0755, NULL, NULL },
{ "proc", 0555, NULL, NULL, true },
{ "sys", 0555, NULL, NULL, true },
{ "dev", 0555, NULL, NULL, true },
/* Various architecture ABIs define the path to the dynamic loader via the /lib64/ subdirectory of
* the root directory. When booting from an otherwise empty root file system (where only /usr/ has
* been mounted into) it is thus necessary to create a symlink pointing to the right subdirectory of
* /usr/ first — otherwise we couldn't invoke any dynamic binary. Let's detect this case here, and
* create the symlink as needed should it be missing. We prefer doing this consistently with Debian's
* multiarch logic, but support Fedora-style and Arch-style multilib too. */
#if defined(__aarch64__)
/* aarch64 ELF ABI actually says dynamic loader is in /lib/, but Fedora puts it in /lib64/ anyway and
* just symlinks /lib/ld-linux-aarch64.so.1 to ../lib64/ld-linux-aarch64.so.1. For this to work
* correctly, /lib64/ must be symlinked to /usr/lib64/. */
{ "lib64", 0, "usr/lib/"LIB_ARCH_TUPLE"\0"
"usr/lib64\0"
"usr/lib\0", "ld-linux-aarch64.so.1" },
# define KNOW_LIB64_DIRS 1
#elif defined(__alpha__)
#elif defined(__arc__) || defined(__tilegx__)
#elif defined(__arm__)
/* No /lib64 on arm. The linker is /lib/ld-linux-armhf.so.3. */
# define KNOW_LIB64_DIRS 1
#elif defined(__i386__) || defined(__x86_64__)
{ "lib64", 0, "usr/lib/"LIB_ARCH_TUPLE"\0"
"usr/lib64\0"
"usr/lib\0", "ld-linux-x86-64.so.2" },
# define KNOW_LIB64_DIRS 1
#elif defined(__ia64__)
#elif defined(__loongarch64)
# define KNOW_LIB64_DIRS 1
# if defined(__loongarch_double_float)
{ "lib64", 0, "usr/lib/"LIB_ARCH_TUPLE"\0"
"usr/lib64\0"
"usr/lib\0", "ld-linux-loongarch-lp64d.so.1" },
# elif defined(__loongarch_single_float)
{ "lib64", 0, "usr/lib/"LIB_ARCH_TUPLE"\0"
"usr/lib64\0"
"usr/lib\0", "ld-linux-loongarch-lp64f.so.1" },
# elif defined(__loongarch_soft_float)
{ "lib64", 0, "usr/lib/"LIB_ARCH_TUPLE"\0"
"usr/lib64\0"
"usr/lib\0", "ld-linux-loongarch-lp64s.so.1" },
# else
# error "Unknown LoongArch ABI"
# endif
#elif defined(__m68k__)
/* No link needed. */
# define KNOW_LIB64_DIRS 1
#elif defined(_MIPS_SIM)
# if _MIPS_SIM == _MIPS_SIM_ABI32
# elif _MIPS_SIM == _MIPS_SIM_NABI32
# elif _MIPS_SIM == _MIPS_SIM_ABI64
# else
# error "Unknown MIPS ABI"
# endif
#elif defined(__powerpc__)
# if defined(__PPC64__) && __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
{ "lib64", 0, "usr/lib/"LIB_ARCH_TUPLE"\0"
"usr/lib64\0"
"usr/lib\0", "ld64.so.2" },
# define KNOW_LIB64_DIRS 1
# elif defined(__powerpc64__) && __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
/* powerpc64-linux-gnu */
# else
/* powerpc-linux-gnu */
# endif
#elif defined(__riscv)
# if __riscv_xlen == 32
# elif __riscv_xlen == 64
/* Same situation as for aarch64 */
{ "lib64", 0, "usr/lib/"LIB_ARCH_TUPLE"\0"
"usr/lib64\0"
"usr/lib\0", "ld-linux-riscv64-lp64d.so.1" },
# define KNOW_LIB64_DIRS 1
# else
# error "Unknown RISC-V ABI"
# endif
#elif defined(__s390__)
/* s390-linux-gnu */
#elif defined(__s390x__)
{ "lib64", 0, "usr/lib/"LIB_ARCH_TUPLE"\0"
"usr/lib64\0"
"usr/lib\0", "ld-lsb-s390x.so.3" },
# define KNOW_LIB64_DIRS 1
#elif defined(__sparc__)
#endif
/* gcc doesn't allow pragma to be used within constructs, hence log about this separately below */
};
#ifndef KNOW_LIB64_DIRS
# pragma message "Please add an entry above specifying whether your architecture uses /lib64/, /lib32/, or no such links."
#endif
int base_filesystem_create_fd(int fd, const char *root, uid_t uid, gid_t gid) {
int r;
assert(fd >= 0);
assert(root);
/* The "root" parameter is decoration only – it's only used as part of log messages */
for (size_t i = 0; i < ELEMENTSOF(table); i++) {
if (faccessat(fd, table[i].dir, F_OK, AT_SYMLINK_NOFOLLOW) >= 0)
continue;
if (table[i].target) {
const char *target = NULL;
/* check if one of the targets exists */
NULSTR_FOREACH(s, table[i].target) {
if (faccessat(fd, s, F_OK, AT_SYMLINK_NOFOLLOW) < 0)
continue;
/* check if a specific file exists at the target path */
if (table[i].exists) {
_cleanup_free_ char *p = NULL;
p = path_join(s, table[i].exists);
if (!p)
return log_oom();
if (faccessat(fd, p, F_OK, AT_SYMLINK_NOFOLLOW) < 0)
continue;
}
target = s;
break;
}
if (!target)
continue;
if (symlinkat(target, fd, table[i].dir) < 0) {
log_full_errno(IN_SET(errno, EEXIST, EROFS) || table[i].ignore_failure ? LOG_DEBUG : LOG_ERR, errno,
"Failed to create symlink at %s/%s: %m", root, table[i].dir);
if (IN_SET(errno, EEXIST, EROFS) || table[i].ignore_failure)
continue;
return -errno;
}
if (uid_is_valid(uid) || gid_is_valid(gid))
if (fchownat(fd, table[i].dir, uid, gid, AT_SYMLINK_NOFOLLOW) < 0)
return log_error_errno(errno, "Failed to chown symlink at %s/%s: %m", root, table[i].dir);
continue;
}
WITH_UMASK(0000)
r = mkdirat(fd, table[i].dir, table[i].mode);
if (r < 0) {
log_full_errno(IN_SET(errno, EEXIST, EROFS) || table[i].ignore_failure ? LOG_DEBUG : LOG_ERR, errno,
"Failed to create directory at %s/%s: %m", root, table[i].dir);
if (IN_SET(errno, EEXIST, EROFS) || table[i].ignore_failure)
continue;
return -errno;
}
if (uid_is_valid(uid) || gid_is_valid(gid))
if (fchownat(fd, table[i].dir, uid, gid, AT_SYMLINK_NOFOLLOW) < 0)
return log_error_errno(errno, "Failed to chown directory at %s/%s: %m", root, table[i].dir);
}
return 0;
}
int base_filesystem_create(const char *root, uid_t uid, gid_t gid) {
_cleanup_close_ int fd = -EBADF;
fd = open(ASSERT_PTR(root), O_DIRECTORY|O_CLOEXEC);
if (fd < 0)
return log_error_errno(errno, "Failed to open root file system: %m");
return base_filesystem_create_fd(fd, root, uid, gid);
}
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