diff options
Diffstat (limited to '')
| -rw-r--r-- | src/basic/mountpoint-util.c | 786 |
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! */ +} |