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-rw-r--r--src/basic/mountpoint-util.c786
1 files changed, 786 insertions, 0 deletions
diff --git a/src/basic/mountpoint-util.c b/src/basic/mountpoint-util.c
new file mode 100644
index 0000000..bf67f7e
--- /dev/null
+++ b/src/basic/mountpoint-util.c
@@ -0,0 +1,786 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <sys/mount.h>
+#if WANT_LINUX_FS_H
+#include <linux/fs.h>
+#endif
+
+#include "alloc-util.h"
+#include "chase.h"
+#include "fd-util.h"
+#include "fileio.h"
+#include "filesystems.h"
+#include "fs-util.h"
+#include "missing_fs.h"
+#include "missing_mount.h"
+#include "missing_stat.h"
+#include "missing_syscall.h"
+#include "mkdir.h"
+#include "mountpoint-util.h"
+#include "nulstr-util.h"
+#include "parse-util.h"
+#include "path-util.h"
+#include "stat-util.h"
+#include "stdio-util.h"
+#include "strv.h"
+#include "user-util.h"
+
+/* This is the original MAX_HANDLE_SZ definition from the kernel, when the API was introduced. We use that in place of
+ * any more currently defined value to future-proof things: if the size is increased in the API headers, and our code
+ * is recompiled then it would cease working on old kernels, as those refuse any sizes larger than this value with
+ * EINVAL right-away. Hence, let's disconnect ourselves from any such API changes, and stick to the original definition
+ * from when it was introduced. We use it as a start value only anyway (see below), and hence should be able to deal
+ * with large file handles anyway. */
+#define ORIGINAL_MAX_HANDLE_SZ 128
+
+int name_to_handle_at_loop(
+ int fd,
+ const char *path,
+ struct file_handle **ret_handle,
+ int *ret_mnt_id,
+ int flags) {
+
+ size_t n = ORIGINAL_MAX_HANDLE_SZ;
+
+ assert((flags & ~(AT_SYMLINK_FOLLOW|AT_EMPTY_PATH)) == 0);
+
+ /* We need to invoke name_to_handle_at() in a loop, given that it might return EOVERFLOW when the specified
+ * buffer is too small. Note that in contrast to what the docs might suggest, MAX_HANDLE_SZ is only good as a
+ * start value, it is not an upper bound on the buffer size required.
+ *
+ * This improves on raw name_to_handle_at() also in one other regard: ret_handle and ret_mnt_id can be passed
+ * as NULL if there's no interest in either. */
+
+ for (;;) {
+ _cleanup_free_ struct file_handle *h = NULL;
+ int mnt_id = -1;
+
+ h = malloc0(offsetof(struct file_handle, f_handle) + n);
+ if (!h)
+ return -ENOMEM;
+
+ h->handle_bytes = n;
+
+ if (name_to_handle_at(fd, strempty(path), h, &mnt_id, flags) >= 0) {
+
+ if (ret_handle)
+ *ret_handle = TAKE_PTR(h);
+
+ if (ret_mnt_id)
+ *ret_mnt_id = mnt_id;
+
+ return 0;
+ }
+ if (errno != EOVERFLOW)
+ return -errno;
+
+ if (!ret_handle && ret_mnt_id && mnt_id >= 0) {
+
+ /* As it appears, name_to_handle_at() fills in mnt_id even when it returns EOVERFLOW when the
+ * buffer is too small, but that's undocumented. Hence, let's make use of this if it appears to
+ * be filled in, and the caller was interested in only the mount ID an nothing else. */
+
+ *ret_mnt_id = mnt_id;
+ return 0;
+ }
+
+ /* If name_to_handle_at() didn't increase the byte size, then this EOVERFLOW is caused by something
+ * else (apparently EOVERFLOW is returned for untriggered nfs4 mounts sometimes), not by the too small
+ * buffer. In that case propagate EOVERFLOW */
+ if (h->handle_bytes <= n)
+ return -EOVERFLOW;
+
+ /* The buffer was too small. Size the new buffer by what name_to_handle_at() returned. */
+ n = h->handle_bytes;
+
+ /* paranoia: check for overflow (note that .handle_bytes is unsigned only) */
+ if (n > UINT_MAX - offsetof(struct file_handle, f_handle))
+ return -EOVERFLOW;
+ }
+}
+
+static int fd_fdinfo_mnt_id(int fd, const char *filename, int flags, int *ret_mnt_id) {
+ char path[STRLEN("/proc/self/fdinfo/") + DECIMAL_STR_MAX(int)];
+ _cleanup_free_ char *fdinfo = NULL;
+ _cleanup_close_ int subfd = -EBADF;
+ char *p;
+ int r;
+
+ assert(ret_mnt_id);
+ assert((flags & ~(AT_SYMLINK_FOLLOW|AT_EMPTY_PATH)) == 0);
+
+ if ((flags & AT_EMPTY_PATH) && isempty(filename))
+ xsprintf(path, "/proc/self/fdinfo/%i", fd);
+ else {
+ subfd = openat(fd, filename, O_CLOEXEC|O_PATH|(flags & AT_SYMLINK_FOLLOW ? 0 : O_NOFOLLOW));
+ if (subfd < 0)
+ return -errno;
+
+ xsprintf(path, "/proc/self/fdinfo/%i", subfd);
+ }
+
+ r = read_full_virtual_file(path, &fdinfo, NULL);
+ if (r == -ENOENT) /* The fdinfo directory is a relatively new addition */
+ return proc_mounted() > 0 ? -EOPNOTSUPP : -ENOSYS;
+ if (r < 0)
+ return r;
+
+ p = find_line_startswith(fdinfo, "mnt_id:");
+ if (!p) /* The mnt_id field is a relatively new addition */
+ return -EOPNOTSUPP;
+
+ p += strspn(p, WHITESPACE);
+ p[strcspn(p, WHITESPACE)] = 0;
+
+ return safe_atoi(p, ret_mnt_id);
+}
+
+static bool filename_possibly_with_slash_suffix(const char *s) {
+ const char *slash, *copied;
+
+ /* Checks whether the specified string is either file name, or a filename with a suffix of
+ * slashes. But nothing else.
+ *
+ * this is OK: foo, bar, foo/, bar/, foo//, bar///
+ * this is not OK: "", "/", "/foo", "foo/bar", ".", ".." … */
+
+ slash = strchr(s, '/');
+ if (!slash)
+ return filename_is_valid(s);
+
+ if (slash - s > PATH_MAX) /* We want to allocate on the stack below, hence do a size check first */
+ return false;
+
+ if (slash[strspn(slash, "/")] != 0) /* Check that the suffix consist only of one or more slashes */
+ return false;
+
+ copied = strndupa_safe(s, slash - s);
+ return filename_is_valid(copied);
+}
+
+static bool is_name_to_handle_at_fatal_error(int err) {
+ /* name_to_handle_at() can return "acceptable" errors that are due to the context. For
+ * example the kernel does not support name_to_handle_at() at all (ENOSYS), or the syscall
+ * was blocked (EACCES/EPERM; maybe through seccomp, because we are running inside of a
+ * container), or the mount point is not triggered yet (EOVERFLOW, think nfs4), or some
+ * general name_to_handle_at() flakiness (EINVAL). However other errors are not supposed to
+ * happen and therefore are considered fatal ones. */
+
+ assert(err < 0);
+
+ return !IN_SET(err, -EOPNOTSUPP, -ENOSYS, -EACCES, -EPERM, -EOVERFLOW, -EINVAL);
+}
+
+int fd_is_mount_point(int fd, const char *filename, int flags) {
+ _cleanup_free_ struct file_handle *h = NULL, *h_parent = NULL;
+ int mount_id = -1, mount_id_parent = -1;
+ bool nosupp = false, check_st_dev = true;
+ STRUCT_STATX_DEFINE(sx);
+ struct stat a, b;
+ int r;
+
+ assert(fd >= 0);
+ assert((flags & ~AT_SYMLINK_FOLLOW) == 0);
+
+ if (!filename) {
+ /* If the file name is specified as NULL we'll see if the specified 'fd' is a mount
+ * point. That's only supported if the kernel supports statx(), or if the inode specified via
+ * 'fd' refers to a directory. Otherwise, we'll have to fail (ENOTDIR), because we have no
+ * kernel API to query the information we need. */
+ flags |= AT_EMPTY_PATH;
+ filename = "";
+ } else if (!filename_possibly_with_slash_suffix(filename))
+ /* Insist that the specified filename is actually a filename, and not a path, i.e. some inode further
+ * up or down the tree then immediately below the specified directory fd. */
+ return -EINVAL;
+
+ /* First we will try statx()' STATX_ATTR_MOUNT_ROOT attribute, which is our ideal API, available
+ * since kernel 5.8.
+ *
+ * If that fails, our second try is the name_to_handle_at() syscall, which tells us the mount id and
+ * an opaque file "handle". It is not supported everywhere though (kernel compile-time option, not
+ * all file systems are hooked up). If it works the mount id is usually good enough to tell us
+ * whether something is a mount point.
+ *
+ * If that didn't work we will try to read the mount id from /proc/self/fdinfo/<fd>. This is almost
+ * as good as name_to_handle_at(), however, does not return the opaque file handle. The opaque file
+ * handle is pretty useful to detect the root directory, which we should always consider a mount
+ * point. Hence we use this only as fallback. Exporting the mnt_id in fdinfo is a pretty recent
+ * kernel addition.
+ *
+ * As last fallback we do traditional fstat() based st_dev comparisons. This is how things were
+ * traditionally done, but unionfs breaks this since it exposes file systems with a variety of st_dev
+ * reported. Also, btrfs subvolumes have different st_dev, even though they aren't real mounts of
+ * their own. */
+
+ if (statx(fd,
+ filename,
+ (FLAGS_SET(flags, AT_SYMLINK_FOLLOW) ? 0 : AT_SYMLINK_NOFOLLOW) |
+ (flags & AT_EMPTY_PATH) |
+ AT_NO_AUTOMOUNT | /* don't trigger automounts – mounts are a local concept, hence no need to trigger automounts to determine STATX_ATTR_MOUNT_ROOT */
+ AT_STATX_DONT_SYNC, /* don't go to the network for this – for similar reasons */
+ STATX_TYPE,
+ &sx) < 0) {
+ if (!ERRNO_IS_NOT_SUPPORTED(errno) && /* statx() is not supported by the kernel. */
+ !ERRNO_IS_PRIVILEGE(errno) && /* maybe filtered by seccomp. */
+ errno != EINVAL) /* glibc's fallback method returns EINVAL when AT_STATX_DONT_SYNC is set. */
+ return -errno;
+
+ /* If statx() is not available or forbidden, fall back to name_to_handle_at() below */
+ } else if (FLAGS_SET(sx.stx_attributes_mask, STATX_ATTR_MOUNT_ROOT)) /* yay! */
+ return FLAGS_SET(sx.stx_attributes, STATX_ATTR_MOUNT_ROOT);
+ else if (FLAGS_SET(sx.stx_mask, STATX_TYPE) && S_ISLNK(sx.stx_mode))
+ return false; /* symlinks are never mount points */
+
+ r = name_to_handle_at_loop(fd, filename, &h, &mount_id, flags);
+ if (r < 0) {
+ if (is_name_to_handle_at_fatal_error(r))
+ return r;
+ if (r != -EOPNOTSUPP)
+ goto fallback_fdinfo;
+
+ /* This kernel or file system does not support name_to_handle_at(), hence let's see
+ * if the upper fs supports it (in which case it is a mount point), otherwise fall
+ * back to the traditional stat() logic */
+ nosupp = true;
+ }
+
+ if (isempty(filename))
+ r = name_to_handle_at_loop(fd, "..", &h_parent, &mount_id_parent, 0); /* can't work for non-directories 😢 */
+ else
+ r = name_to_handle_at_loop(fd, "", &h_parent, &mount_id_parent, AT_EMPTY_PATH);
+ if (r < 0) {
+ if (is_name_to_handle_at_fatal_error(r))
+ return r;
+ if (r != -EOPNOTSUPP)
+ goto fallback_fdinfo;
+ if (nosupp)
+ /* Both the parent and the directory can't do name_to_handle_at() */
+ goto fallback_fdinfo;
+
+ /* The parent can't do name_to_handle_at() but the directory we are
+ * interested in can? If so, it must be a mount point. */
+ return 1;
+ }
+
+ /* The parent can do name_to_handle_at() but the directory we are interested in can't? If
+ * so, it must be a mount point. */
+ if (nosupp)
+ return 1;
+
+ /* If the file handle for the directory we are interested in and its parent are identical,
+ * we assume this is the root directory, which is a mount point. */
+
+ if (h->handle_type == h_parent->handle_type &&
+ memcmp_nn(h->f_handle, h->handle_bytes,
+ h_parent->f_handle, h_parent->handle_bytes) == 0)
+ return 1;
+
+ return mount_id != mount_id_parent;
+
+fallback_fdinfo:
+ r = fd_fdinfo_mnt_id(fd, filename, flags, &mount_id);
+ if (IN_SET(r, -EOPNOTSUPP, -EACCES, -EPERM, -ENOSYS))
+ goto fallback_fstat;
+ if (r < 0)
+ return r;
+
+ if (isempty(filename))
+ r = fd_fdinfo_mnt_id(fd, "..", 0, &mount_id_parent); /* can't work for non-directories 😢 */
+ else
+ r = fd_fdinfo_mnt_id(fd, "", AT_EMPTY_PATH, &mount_id_parent);
+ if (r < 0)
+ return r;
+
+ if (mount_id != mount_id_parent)
+ return 1;
+
+ /* Hmm, so, the mount ids are the same. This leaves one special case though for the root file
+ * system. For that, let's see if the parent directory has the same inode as we are interested
+ * in. Hence, let's also do fstat() checks now, too, but avoid the st_dev comparisons, since they
+ * aren't that useful on unionfs mounts. */
+ check_st_dev = false;
+
+fallback_fstat:
+ /* yay for fstatat() taking a different set of flags than the other _at() above */
+ if (flags & AT_SYMLINK_FOLLOW)
+ flags &= ~AT_SYMLINK_FOLLOW;
+ else
+ flags |= AT_SYMLINK_NOFOLLOW;
+ if (fstatat(fd, filename, &a, flags) < 0)
+ return -errno;
+ if (S_ISLNK(a.st_mode)) /* Symlinks are never mount points */
+ return false;
+
+ if (isempty(filename))
+ r = fstatat(fd, "..", &b, 0);
+ else
+ r = fstatat(fd, "", &b, AT_EMPTY_PATH);
+ if (r < 0)
+ return -errno;
+
+ /* A directory with same device and inode as its parent? Must be the root directory */
+ if (stat_inode_same(&a, &b))
+ return 1;
+
+ return check_st_dev && (a.st_dev != b.st_dev);
+}
+
+/* flags can be AT_SYMLINK_FOLLOW or 0 */
+int path_is_mount_point(const char *t, const char *root, int flags) {
+ _cleanup_free_ char *canonical = NULL;
+ _cleanup_close_ int fd = -EBADF;
+ int r;
+
+ assert(t);
+ assert((flags & ~AT_SYMLINK_FOLLOW) == 0);
+
+ if (path_equal(t, "/"))
+ return 1;
+
+ /* we need to resolve symlinks manually, we can't just rely on
+ * fd_is_mount_point() to do that for us; if we have a structure like
+ * /bin -> /usr/bin/ and /usr is a mount point, then the parent that we
+ * look at needs to be /usr, not /. */
+ if (flags & AT_SYMLINK_FOLLOW) {
+ r = chase(t, root, CHASE_TRAIL_SLASH, &canonical, NULL);
+ if (r < 0)
+ return r;
+
+ t = canonical;
+ }
+
+ fd = open_parent(t, O_PATH|O_CLOEXEC, 0);
+ if (fd < 0)
+ return fd;
+
+ return fd_is_mount_point(fd, last_path_component(t), flags);
+}
+
+int path_get_mnt_id_at_fallback(int dir_fd, const char *path, int *ret) {
+ int r;
+
+ assert(dir_fd >= 0 || dir_fd == AT_FDCWD);
+ assert(ret);
+
+ r = name_to_handle_at_loop(dir_fd, path, NULL, ret, isempty(path) ? AT_EMPTY_PATH : 0);
+ if (r == 0 || is_name_to_handle_at_fatal_error(r))
+ return r;
+
+ return fd_fdinfo_mnt_id(dir_fd, path, isempty(path) ? AT_EMPTY_PATH : 0, ret);
+}
+
+int path_get_mnt_id_at(int dir_fd, const char *path, int *ret) {
+ STRUCT_NEW_STATX_DEFINE(buf);
+
+ assert(dir_fd >= 0 || dir_fd == AT_FDCWD);
+ assert(ret);
+
+ if (statx(dir_fd,
+ strempty(path),
+ (isempty(path) ? AT_EMPTY_PATH : AT_SYMLINK_NOFOLLOW) |
+ AT_NO_AUTOMOUNT | /* don't trigger automounts, mnt_id is a local concept */
+ AT_STATX_DONT_SYNC, /* don't go to the network, mnt_id is a local concept */
+ STATX_MNT_ID,
+ &buf.sx) < 0) {
+ if (!ERRNO_IS_NOT_SUPPORTED(errno) && /* statx() is not supported by the kernel. */
+ !ERRNO_IS_PRIVILEGE(errno) && /* maybe filtered by seccomp. */
+ errno != EINVAL) /* glibc's fallback method returns EINVAL when AT_STATX_DONT_SYNC is set. */
+ return -errno;
+
+ /* Fall back to name_to_handle_at() and then fdinfo if statx is not supported or we lack
+ * privileges */
+
+ } else if (FLAGS_SET(buf.nsx.stx_mask, STATX_MNT_ID)) {
+ *ret = buf.nsx.stx_mnt_id;
+ return 0;
+ }
+
+ return path_get_mnt_id_at_fallback(dir_fd, path, ret);
+}
+
+bool fstype_is_network(const char *fstype) {
+ const char *x;
+
+ x = startswith(fstype, "fuse.");
+ if (x)
+ fstype = x;
+
+ if (nulstr_contains(filesystem_sets[FILESYSTEM_SET_NETWORK].value, fstype))
+ return true;
+
+ /* Filesystems not present in the internal database */
+ return STR_IN_SET(fstype,
+ "davfs",
+ "glusterfs",
+ "lustre",
+ "sshfs");
+}
+
+bool fstype_needs_quota(const char *fstype) {
+ /* 1. quotacheck needs to be run for some filesystems after they are mounted
+ * if the filesystem was not unmounted cleanly.
+ * 2. You may need to run quotaon to enable quota usage tracking and/or
+ * enforcement.
+ * ext2 - needs 1) and 2)
+ * ext3 - needs 2) if configured using usrjquota/grpjquota mount options
+ * ext4 - needs 1) if created without journal, needs 2) if created without QUOTA
+ * filesystem feature
+ * reiserfs - needs 2).
+ * jfs - needs 2)
+ * f2fs - needs 2) if configured using usrjquota/grpjquota/prjjquota mount options
+ * xfs - nothing needed
+ * gfs2 - nothing needed
+ * ocfs2 - nothing needed
+ * btrfs - nothing needed
+ * for reference see filesystem and quota manpages */
+ return STR_IN_SET(fstype,
+ "ext2",
+ "ext3",
+ "ext4",
+ "reiserfs",
+ "jfs",
+ "f2fs");
+}
+
+bool fstype_is_api_vfs(const char *fstype) {
+ const FilesystemSet *fs;
+
+ FOREACH_POINTER(fs,
+ filesystem_sets + FILESYSTEM_SET_BASIC_API,
+ filesystem_sets + FILESYSTEM_SET_AUXILIARY_API,
+ filesystem_sets + FILESYSTEM_SET_PRIVILEGED_API,
+ filesystem_sets + FILESYSTEM_SET_TEMPORARY)
+ if (nulstr_contains(fs->value, fstype))
+ return true;
+
+ /* Filesystems not present in the internal database */
+ return STR_IN_SET(fstype,
+ "autofs",
+ "cpuset",
+ "devtmpfs");
+}
+
+bool fstype_is_blockdev_backed(const char *fstype) {
+ const char *x;
+
+ x = startswith(fstype, "fuse.");
+ if (x)
+ fstype = x;
+
+ return !streq(fstype, "9p") && !fstype_is_network(fstype) && !fstype_is_api_vfs(fstype);
+}
+
+bool fstype_is_ro(const char *fstype) {
+ /* All Linux file systems that are necessarily read-only */
+ return STR_IN_SET(fstype,
+ "DM_verity_hash",
+ "cramfs",
+ "erofs",
+ "iso9660",
+ "squashfs");
+}
+
+bool fstype_can_discard(const char *fstype) {
+ assert(fstype);
+
+ /* Use a curated list as first check, to avoid calling fsopen() which might load kmods, which might
+ * not be allowed in our MAC context. */
+ if (STR_IN_SET(fstype, "btrfs", "f2fs", "ext4", "vfat", "xfs"))
+ return true;
+
+ /* On new kernels we can just ask the kernel */
+ return mount_option_supported(fstype, "discard", NULL) > 0;
+}
+
+bool fstype_can_norecovery(const char *fstype) {
+ assert(fstype);
+
+ /* Use a curated list as first check, to avoid calling fsopen() which might load kmods, which might
+ * not be allowed in our MAC context. */
+ if (STR_IN_SET(fstype, "ext3", "ext4", "xfs", "btrfs"))
+ return true;
+
+ /* On new kernels we can just ask the kernel */
+ return mount_option_supported(fstype, "norecovery", NULL) > 0;
+}
+
+bool fstype_can_umask(const char *fstype) {
+ assert(fstype);
+
+ /* Use a curated list as first check, to avoid calling fsopen() which might load kmods, which might
+ * not be allowed in our MAC context. If we don't know ourselves, on new kernels we can just ask the
+ * kernel. */
+ return streq(fstype, "vfat") || mount_option_supported(fstype, "umask", "0077") > 0;
+}
+
+bool fstype_can_uid_gid(const char *fstype) {
+ /* All file systems that have a uid=/gid= mount option that fixates the owners of all files and
+ * directories, current and future. Note that this does *not* ask the kernel via
+ * mount_option_supported() here because the uid=/gid= setting of various file systems mean different
+ * things: some apply it only to the root dir inode, others to all inodes in the file system. Thus we
+ * maintain the curated list below. 😢 */
+
+ return STR_IN_SET(fstype,
+ "adfs",
+ "exfat",
+ "fat",
+ "hfs",
+ "hpfs",
+ "iso9660",
+ "msdos",
+ "ntfs",
+ "vfat");
+}
+
+int dev_is_devtmpfs(void) {
+ _cleanup_fclose_ FILE *proc_self_mountinfo = NULL;
+ int mount_id, r;
+ char *e;
+
+ r = path_get_mnt_id("/dev", &mount_id);
+ if (r < 0)
+ return r;
+
+ r = fopen_unlocked("/proc/self/mountinfo", "re", &proc_self_mountinfo);
+ if (r == -ENOENT)
+ return proc_mounted() > 0 ? -ENOENT : -ENOSYS;
+ if (r < 0)
+ return r;
+
+ for (;;) {
+ _cleanup_free_ char *line = NULL;
+ int mid;
+
+ r = read_line(proc_self_mountinfo, LONG_LINE_MAX, &line);
+ if (r < 0)
+ return r;
+ if (r == 0)
+ break;
+
+ if (sscanf(line, "%i", &mid) != 1)
+ continue;
+
+ if (mid != mount_id)
+ continue;
+
+ e = strstrafter(line, " - ");
+ if (!e)
+ continue;
+
+ /* accept any name that starts with the currently expected type */
+ if (startswith(e, "devtmpfs"))
+ return true;
+ }
+
+ return false;
+}
+
+int mount_fd(const char *source,
+ int target_fd,
+ const char *filesystemtype,
+ unsigned long mountflags,
+ const void *data) {
+
+ if (mount(source, FORMAT_PROC_FD_PATH(target_fd), filesystemtype, mountflags, data) < 0) {
+ if (errno != ENOENT)
+ return -errno;
+
+ /* ENOENT can mean two things: either that the source is missing, or that /proc/ isn't
+ * mounted. Check for the latter to generate better error messages. */
+ if (proc_mounted() == 0)
+ return -ENOSYS;
+
+ return -ENOENT;
+ }
+
+ return 0;
+}
+
+int mount_nofollow(
+ const char *source,
+ const char *target,
+ const char *filesystemtype,
+ unsigned long mountflags,
+ const void *data) {
+
+ _cleanup_close_ int fd = -EBADF;
+
+ /* In almost all cases we want to manipulate the mount table without following symlinks, hence
+ * mount_nofollow() is usually the way to go. The only exceptions are environments where /proc/ is
+ * not available yet, since we need /proc/self/fd/ for this logic to work. i.e. during the early
+ * initialization of namespacing/container stuff where /proc is not yet mounted (and maybe even the
+ * fs to mount) we can only use traditional mount() directly.
+ *
+ * Note that this disables following only for the final component of the target, i.e symlinks within
+ * the path of the target are honoured, as are symlinks in the source path everywhere. */
+
+ fd = open(target, O_PATH|O_CLOEXEC|O_NOFOLLOW);
+ if (fd < 0)
+ return -errno;
+
+ return mount_fd(source, fd, filesystemtype, mountflags, data);
+}
+
+const char *mount_propagation_flag_to_string(unsigned long flags) {
+
+ switch (flags & (MS_SHARED|MS_SLAVE|MS_PRIVATE)) {
+ case 0:
+ return "";
+ case MS_SHARED:
+ return "shared";
+ case MS_SLAVE:
+ return "slave";
+ case MS_PRIVATE:
+ return "private";
+ }
+
+ return NULL;
+}
+
+int mount_propagation_flag_from_string(const char *name, unsigned long *ret) {
+
+ if (isempty(name))
+ *ret = 0;
+ else if (streq(name, "shared"))
+ *ret = MS_SHARED;
+ else if (streq(name, "slave"))
+ *ret = MS_SLAVE;
+ else if (streq(name, "private"))
+ *ret = MS_PRIVATE;
+ else
+ return -EINVAL;
+ return 0;
+}
+
+bool mount_propagation_flag_is_valid(unsigned long flag) {
+ return IN_SET(flag, 0, MS_SHARED, MS_PRIVATE, MS_SLAVE);
+}
+
+bool mount_new_api_supported(void) {
+ static int cache = -1;
+ int r;
+
+ if (cache >= 0)
+ return cache;
+
+ /* This is the newer API among the ones we use, so use it as boundary */
+ r = RET_NERRNO(mount_setattr(-EBADF, NULL, 0, NULL, 0));
+ if (r == 0 || ERRNO_IS_NOT_SUPPORTED(r)) /* This should return an error if it is working properly */
+ return (cache = false);
+
+ return (cache = true);
+}
+
+unsigned long ms_nosymfollow_supported(void) {
+ _cleanup_close_ int fsfd = -EBADF, mntfd = -EBADF;
+ static int cache = -1;
+
+ /* Returns MS_NOSYMFOLLOW if it is supported, zero otherwise. */
+
+ if (cache >= 0)
+ return cache ? MS_NOSYMFOLLOW : 0;
+
+ if (!mount_new_api_supported())
+ goto not_supported;
+
+ /* Checks if MS_NOSYMFOLLOW is supported (which was added in 5.10). We use the new mount API's
+ * mount_setattr() call for that, which was added in 5.12, which is close enough. */
+
+ fsfd = fsopen("tmpfs", FSOPEN_CLOEXEC);
+ if (fsfd < 0) {
+ if (ERRNO_IS_NOT_SUPPORTED(errno))
+ goto not_supported;
+
+ log_debug_errno(errno, "Failed to open superblock context for tmpfs: %m");
+ return 0;
+ }
+
+ if (fsconfig(fsfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0) < 0) {
+ if (ERRNO_IS_NOT_SUPPORTED(errno))
+ goto not_supported;
+
+ log_debug_errno(errno, "Failed to create tmpfs superblock: %m");
+ return 0;
+ }
+
+ mntfd = fsmount(fsfd, FSMOUNT_CLOEXEC, 0);
+ if (mntfd < 0) {
+ if (ERRNO_IS_NOT_SUPPORTED(errno))
+ goto not_supported;
+
+ log_debug_errno(errno, "Failed to turn superblock fd into mount fd: %m");
+ return 0;
+ }
+
+ if (mount_setattr(mntfd, "", AT_EMPTY_PATH|AT_RECURSIVE,
+ &(struct mount_attr) {
+ .attr_set = MOUNT_ATTR_NOSYMFOLLOW,
+ }, sizeof(struct mount_attr)) < 0) {
+ if (ERRNO_IS_NOT_SUPPORTED(errno))
+ goto not_supported;
+
+ log_debug_errno(errno, "Failed to set MOUNT_ATTR_NOSYMFOLLOW mount attribute: %m");
+ return 0;
+ }
+
+ cache = true;
+ return MS_NOSYMFOLLOW;
+
+not_supported:
+ cache = false;
+ return 0;
+}
+
+int mount_option_supported(const char *fstype, const char *key, const char *value) {
+ _cleanup_close_ int fd = -EBADF;
+ int r;
+
+ /* Checks if the specified file system supports a mount option. Returns > 0 if it supports it, == 0 if
+ * it does not. Return -EAGAIN if we can't determine it. And any other error otherwise. */
+
+ assert(fstype);
+ assert(key);
+
+ fd = fsopen(fstype, FSOPEN_CLOEXEC);
+ if (fd < 0) {
+ if (ERRNO_IS_NOT_SUPPORTED(errno))
+ return -EAGAIN; /* new mount API not available → don't know */
+
+ return log_debug_errno(errno, "Failed to open superblock context for '%s': %m", fstype);
+ }
+
+ /* Various file systems have not been converted to the new mount API yet. For such file systems
+ * fsconfig() with FSCONFIG_SET_STRING/FSCONFIG_SET_FLAG never fail. Which sucks, because we want to
+ * use it for testing support, after all. Let's hence do a check if the file system got converted yet
+ * first. */
+ if (fsconfig(fd, FSCONFIG_SET_FD, "adefinitelynotexistingmountoption", NULL, fd) < 0) {
+ /* If FSCONFIG_SET_FD is not supported for the fs, then the file system was not converted to
+ * the new mount API yet. If it returns EINVAL the mount option doesn't exist, but the fstype
+ * is converted. */
+ if (errno == EOPNOTSUPP)
+ return -EAGAIN; /* FSCONFIG_SET_FD not supported on the fs, hence not converted to new mount API → don't know */
+ if (errno != EINVAL)
+ return log_debug_errno(errno, "Failed to check if file system has been converted to new mount API: %m");
+
+ /* So FSCONFIG_SET_FD worked, but the option didn't exist (we got EINVAL), this means the fs
+ * is converted. Let's now ask the actual question we wonder about. */
+ } else
+ return log_debug_errno(SYNTHETIC_ERRNO(EAGAIN), "FSCONFIG_SET_FD worked unexpectedly for '%s', whoa!", fstype);
+
+ if (value)
+ r = fsconfig(fd, FSCONFIG_SET_STRING, key, value, 0);
+ else
+ r = fsconfig(fd, FSCONFIG_SET_FLAG, key, NULL, 0);
+ if (r < 0) {
+ if (errno == EINVAL)
+ return false; /* EINVAL means option not supported. */
+
+ return log_debug_errno(errno, "Failed to set '%s%s%s' on '%s' superblock context: %m",
+ key, value ? "=" : "", strempty(value), fstype);
+ }
+
+ return true; /* works! */
+}