From 4349cd7c1d153c4ffa23cf1cff1644e0afa9bcf0 Mon Sep 17 00:00:00 2001 From: Lennart Poettering Date: Mon, 26 Oct 2015 18:44:13 +0100 Subject: util-lib: move mount related utility calls to mount-util.[ch] --- src/basic/mount-util.c | 483 +++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 483 insertions(+) create mode 100644 src/basic/mount-util.c (limited to 'src/basic/mount-util.c') diff --git a/src/basic/mount-util.c b/src/basic/mount-util.c new file mode 100644 index 0000000000..6b33d43024 --- /dev/null +++ b/src/basic/mount-util.c @@ -0,0 +1,483 @@ +/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/ + +/*** + This file is part of systemd. + + Copyright 2010 Lennart Poettering + + systemd is free software; you can redistribute it and/or modify it + under the terms of the GNU Lesser General Public License as published by + the Free Software Foundation; either version 2.1 of the License, or + (at your option) any later version. + + systemd is distributed in the hope that it will be useful, but + WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public License + along with systemd; If not, see . +***/ + +#include +#include +#include + +#include "escape.h" +#include "fd-util.h" +#include "fileio.h" +#include "mount-util.h" +#include "parse-util.h" +#include "path-util.h" +#include "set.h" +#include "string-util.h" +#include "util.h" + +static int fd_fdinfo_mnt_id(int fd, const char *filename, int flags, int *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; + + if ((flags & AT_EMPTY_PATH) && isempty(filename)) + xsprintf(path, "/proc/self/fdinfo/%i", fd); + else { + subfd = openat(fd, filename, O_RDONLY|O_CLOEXEC|O_NOCTTY|O_PATH); + 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 -errno; + + 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, mnt_id); +} + + +int fd_is_mount_point(int fd, const char *filename, int flags) { + union file_handle_union h = FILE_HANDLE_INIT, h_parent = FILE_HANDLE_INIT; + int mount_id = -1, mount_id_parent = -1; + bool nosupp = false, check_st_dev = true; + struct stat a, b; + int r; + + assert(fd >= 0); + assert(filename); + + /* First we will try 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 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. */ + + r = name_to_handle_at(fd, filename, &h.handle, &mount_id, flags); + if (r < 0) { + if (errno == ENOSYS) + /* This kernel does not support name_to_handle_at() + * fall back to simpler logic. */ + goto fallback_fdinfo; + else if (errno == 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 fallback to the + * traditional stat() logic */ + nosupp = true; + else + return -errno; + } + + r = name_to_handle_at(fd, "", &h_parent.handle, &mount_id_parent, AT_EMPTY_PATH); + if (r < 0) { + if (errno == 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 + return -errno; + } + + /* 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.handle_bytes == h_parent.handle.handle_bytes && + h.handle.handle_type == h_parent.handle.handle_type && + memcmp(h.handle.f_handle, h_parent.handle.f_handle, h.handle.handle_bytes) == 0) + return 1; + + return mount_id != mount_id_parent; + +fallback_fdinfo: + r = fd_fdinfo_mnt_id(fd, filename, flags, &mount_id); + if (r == -EOPNOTSUPP) + 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, int flags) { + _cleanup_close_ int fd = -1; + _cleanup_free_ char *canonical = NULL, *parent = NULL; + + assert(t); + + 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) { + canonical = canonicalize_file_name(t); + if (!canonical) + return -errno; + + t = canonical; + } + + parent = dirname_malloc(t); + if (!parent) + return -ENOMEM; + + fd = openat(AT_FDCWD, parent, O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC|O_PATH); + if (fd < 0) + return -errno; + + return fd_is_mount_point(fd, basename(t), flags); +} + +int umount_recursive(const char *prefix, int flags) { + bool again; + int n = 0, r; + + /* Try to umount everything recursively below a + * directory. Also, take care of stacked mounts, and keep + * unmounting them until they are gone. */ + + do { + _cleanup_fclose_ FILE *proc_self_mountinfo = NULL; + + again = false; + r = 0; + + proc_self_mountinfo = fopen("/proc/self/mountinfo", "re"); + if (!proc_self_mountinfo) + return -errno; + + for (;;) { + _cleanup_free_ char *path = NULL, *p = NULL; + int k; + + k = fscanf(proc_self_mountinfo, + "%*s " /* (1) mount id */ + "%*s " /* (2) parent id */ + "%*s " /* (3) major:minor */ + "%*s " /* (4) root */ + "%ms " /* (5) mount point */ + "%*s" /* (6) mount options */ + "%*[^-]" /* (7) optional fields */ + "- " /* (8) separator */ + "%*s " /* (9) file system type */ + "%*s" /* (10) mount source */ + "%*s" /* (11) mount options 2 */ + "%*[^\n]", /* some rubbish at the end */ + &path); + if (k != 1) { + if (k == EOF) + break; + + continue; + } + + r = cunescape(path, UNESCAPE_RELAX, &p); + if (r < 0) + return r; + + if (!path_startswith(p, prefix)) + continue; + + if (umount2(p, flags) < 0) { + r = -errno; + continue; + } + + again = true; + n++; + + break; + } + + } while (again); + + return r ? r : n; +} + +static int get_mount_flags(const char *path, unsigned long *flags) { + struct statvfs buf; + + if (statvfs(path, &buf) < 0) + return -errno; + *flags = buf.f_flag; + return 0; +} + +int bind_remount_recursive(const char *prefix, bool ro) { + _cleanup_set_free_free_ Set *done = NULL; + _cleanup_free_ char *cleaned = NULL; + int r; + + /* Recursively remount a directory (and all its submounts) + * read-only or read-write. If the directory is already + * mounted, we reuse the mount and simply mark it + * MS_BIND|MS_RDONLY (or remove the MS_RDONLY for read-write + * operation). If it isn't we first make it one. Afterwards we + * apply MS_BIND|MS_RDONLY (or remove MS_RDONLY) to all + * submounts we can access, too. When mounts are stacked on + * the same mount point we only care for each individual + * "top-level" mount on each point, as we cannot + * influence/access the underlying mounts anyway. We do not + * have any effect on future submounts that might get + * propagated, they migt be writable. This includes future + * submounts that have been triggered via autofs. */ + + cleaned = strdup(prefix); + if (!cleaned) + return -ENOMEM; + + path_kill_slashes(cleaned); + + done = set_new(&string_hash_ops); + if (!done) + return -ENOMEM; + + for (;;) { + _cleanup_fclose_ FILE *proc_self_mountinfo = NULL; + _cleanup_set_free_free_ Set *todo = NULL; + bool top_autofs = false; + char *x; + unsigned long orig_flags; + + todo = set_new(&string_hash_ops); + if (!todo) + return -ENOMEM; + + proc_self_mountinfo = fopen("/proc/self/mountinfo", "re"); + if (!proc_self_mountinfo) + return -errno; + + for (;;) { + _cleanup_free_ char *path = NULL, *p = NULL, *type = NULL; + int k; + + k = fscanf(proc_self_mountinfo, + "%*s " /* (1) mount id */ + "%*s " /* (2) parent id */ + "%*s " /* (3) major:minor */ + "%*s " /* (4) root */ + "%ms " /* (5) mount point */ + "%*s" /* (6) mount options (superblock) */ + "%*[^-]" /* (7) optional fields */ + "- " /* (8) separator */ + "%ms " /* (9) file system type */ + "%*s" /* (10) mount source */ + "%*s" /* (11) mount options (bind mount) */ + "%*[^\n]", /* some rubbish at the end */ + &path, + &type); + if (k != 2) { + if (k == EOF) + break; + + continue; + } + + r = cunescape(path, UNESCAPE_RELAX, &p); + if (r < 0) + return r; + + /* Let's ignore autofs mounts. If they aren't + * triggered yet, we want to avoid triggering + * them, as we don't make any guarantees for + * future submounts anyway. If they are + * already triggered, then we will find + * another entry for this. */ + if (streq(type, "autofs")) { + top_autofs = top_autofs || path_equal(cleaned, p); + continue; + } + + if (path_startswith(p, cleaned) && + !set_contains(done, p)) { + + r = set_consume(todo, p); + p = NULL; + + if (r == -EEXIST) + continue; + if (r < 0) + return r; + } + } + + /* If we have no submounts to process anymore and if + * the root is either already done, or an autofs, we + * are done */ + if (set_isempty(todo) && + (top_autofs || set_contains(done, cleaned))) + return 0; + + if (!set_contains(done, cleaned) && + !set_contains(todo, cleaned)) { + /* The prefix directory itself is not yet a + * mount, make it one. */ + if (mount(cleaned, cleaned, NULL, MS_BIND|MS_REC, NULL) < 0) + return -errno; + + orig_flags = 0; + (void) get_mount_flags(cleaned, &orig_flags); + orig_flags &= ~MS_RDONLY; + + if (mount(NULL, prefix, NULL, orig_flags|MS_BIND|MS_REMOUNT|(ro ? MS_RDONLY : 0), NULL) < 0) + return -errno; + + x = strdup(cleaned); + if (!x) + return -ENOMEM; + + r = set_consume(done, x); + if (r < 0) + return r; + } + + while ((x = set_steal_first(todo))) { + + r = set_consume(done, x); + if (r == -EEXIST || r == 0) + continue; + if (r < 0) + return r; + + /* Try to reuse the original flag set, but + * don't care for errors, in case of + * obstructed mounts */ + orig_flags = 0; + (void) get_mount_flags(x, &orig_flags); + orig_flags &= ~MS_RDONLY; + + if (mount(NULL, x, NULL, orig_flags|MS_BIND|MS_REMOUNT|(ro ? MS_RDONLY : 0), NULL) < 0) { + + /* Deal with mount points that are + * obstructed by a later mount */ + + if (errno != ENOENT) + return -errno; + } + + } + } +} + +int mount_move_root(const char *path) { + assert(path); + + if (chdir(path) < 0) + return -errno; + + if (mount(path, "/", NULL, MS_MOVE, NULL) < 0) + return -errno; + + if (chroot(".") < 0) + return -errno; + + if (chdir("/") < 0) + return -errno; + + return 0; +} -- cgit v1.2.3-54-g00ecf