/* SPDX-License-Identifier: LGPL-2.1+ */ #include #include #include #include "alloc-util.h" #include "fd-util.h" #include "fileio.h" #include "fs-util.h" #include "missing_stat.h" #include "missing_syscall.h" #include "mountpoint-util.h" #include "parse-util.h" #include "path-util.h" #include "stdio-util.h" #include "strv.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) { _cleanup_free_ struct file_handle *h = NULL; 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 (;;) { 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, 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; if (offsetof(struct file_handle, f_handle) + n < n) /* check for addition overflow */ return -EOVERFLOW; h = mfree(h); } } 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 = -1; 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_file(path, &fdinfo, NULL); if (r == -ENOENT) /* The fdinfo directory is a relatively new addition */ return -EOPNOTSUPP; if (r < 0) return r; p = startswith(fdinfo, "mnt_id:"); if (!p) { p = strstr(fdinfo, "\nmnt_id:"); if (!p) /* The mnt_id field is a relatively new addition */ return -EOPNOTSUPP; p += 8; } p += strspn(p, WHITESPACE); p[strcspn(p, WHITESPACE)] = 0; return safe_atoi(p, ret_mnt_id); } 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 stat a, b; struct statx sx #if HAS_FEATURE_MEMORY_SANITIZER = {} # warning "Explicitly initializing struct statx, to work around msan limitation. Please remove as soon as msan has been updated to not require this." #endif ; int r; assert(fd >= 0); assert(filename); assert((flags & ~(AT_SYMLINK_FOLLOW|AT_EMPTY_PATH)) == 0); /* 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/. 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, 0, &sx) < 0) { if (!ERRNO_IS_NOT_SUPPORTED(errno) && !ERRNO_IS_PRIVILEGE(errno)) 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); r = name_to_handle_at_loop(fd, filename, &h, &mount_id, flags); if (IN_SET(r, -ENOSYS, -EACCES, -EPERM, -EOVERFLOW, -EINVAL)) /* This 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): fall back to simpler logic. */ goto fallback_fdinfo; else if (r == -EOPNOTSUPP) /* 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; else if (r < 0) return r; r = name_to_handle_at_loop(fd, "", &h_parent, &mount_id_parent, AT_EMPTY_PATH); if (r == -EOPNOTSUPP) { if (nosupp) /* Neither parent nor child do name_to_handle_at()? We have no choice but to fall back. */ goto fallback_fdinfo; else /* 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; } else if (r < 0) return r; /* 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_bytes == h_parent->handle_bytes && h->handle_type == h_parent->handle_type && memcmp(h->f_handle, h_parent->f_handle, h->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)) goto fallback_fstat; if (r < 0) return r; 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 (fstatat(fd, "", &b, AT_EMPTY_PATH) < 0) return -errno; /* A directory with same device and inode as its parent? Must * be the root directory */ if (a.st_dev == b.st_dev && a.st_ino == b.st_ino) 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 = -1; 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_symlinks(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(const char *path, int *ret) { union { struct statx sx; struct new_statx nsx; } buf #if HAS_FEATURE_MEMORY_SANITIZER = {} # warning "Explicitly initializing struct statx, to work around msan limitation. Please remove as soon as msan has been updated to not require this." #endif ; int r; if (statx(AT_FDCWD, path, AT_SYMLINK_NOFOLLOW|AT_NO_AUTOMOUNT, STATX_MNT_ID, &buf.sx) < 0) { if (!ERRNO_IS_NOT_SUPPORTED(errno) && !ERRNO_IS_PRIVILEGE(errno)) 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; } r = name_to_handle_at_loop(AT_FDCWD, path, NULL, ret, 0); if (IN_SET(r, -EOPNOTSUPP, -ENOSYS, -EACCES, -EPERM, -EOVERFLOW, -EINVAL)) /* kernel/fs don't support this, or seccomp blocks access, or untriggered mount, or name_to_handle_at() is flaky */ return fd_fdinfo_mnt_id(AT_FDCWD, path, 0, ret); return r; } bool fstype_is_network(const char *fstype) { const char *x; x = startswith(fstype, "fuse."); if (x) fstype = x; return STR_IN_SET(fstype, "afs", "ceph", "cifs", "smb3", "smbfs", "sshfs", "ncpfs", "ncp", "nfs", "nfs4", "gfs", "gfs2", "glusterfs", "pvfs2", /* OrangeFS */ "ocfs2", "lustre", "davfs"); } bool fstype_is_api_vfs(const char *fstype) { return STR_IN_SET(fstype, "autofs", "bpf", "cgroup", "cgroup2", "configfs", "cpuset", "debugfs", "devpts", "devtmpfs", "efivarfs", "fusectl", "hugetlbfs", "mqueue", "proc", "pstore", "ramfs", "securityfs", "sysfs", "tmpfs", "tracefs"); } 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", "iso9660", "squashfs"); } bool fstype_can_discard(const char *fstype) { return STR_IN_SET(fstype, "btrfs", "ext4", "vfat", "xfs"); } 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. */ 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 < 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 = strstr(line, " - "); if (!e) continue; /* accept any name that starts with the currently expected type */ if (startswith(e + 3, "devtmpfs")) return true; } return false; } const char *mount_propagation_flags_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_flags_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; }