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-rw-r--r--src/basic/mountpoint-util.c444
1 files changed, 444 insertions, 0 deletions
diff --git a/src/basic/mountpoint-util.c b/src/basic/mountpoint-util.c
new file mode 100644
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+++ b/src/basic/mountpoint-util.c
@@ -0,0 +1,444 @@
+/* SPDX-License-Identifier: LGPL-2.1+ */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <stdio_ext.h>
+#include <sys/mount.h>
+
+#include "alloc-util.h"
+#include "fd-util.h"
+#include "fileio.h"
+#include "fs-util.h"
+#include "missing.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;
+
+ /* 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 *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_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, 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;
+ 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/<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. */
+
+ 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 fallback 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);
+ if (r < 0)
+ return r;
+
+ t = canonical;
+ }
+
+ fd = open_parent(t, O_PATH|O_CLOEXEC, 0);
+ if (fd < 0)
+ return -errno;
+
+ return fd_is_mount_point(fd, last_path_component(t), flags);
+}
+
+int path_get_mnt_id(const char *path, int *ret) {
+ int r;
+
+ 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",
+ "cifs",
+ "smbfs",
+ "sshfs",
+ "ncpfs",
+ "ncp",
+ "nfs",
+ "nfs4",
+ "gfs",
+ "gfs2",
+ "glusterfs",
+ "pvfs2", /* OrangeFS */
+ "ocfs2",
+ "lustre");
+}
+
+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_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",
+ "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;
+
+ proc_self_mountinfo = fopen("/proc/self/mountinfo", "re");
+ if (!proc_self_mountinfo)
+ return -errno;
+
+ (void) __fsetlocking(proc_self_mountinfo, FSETLOCKING_BYCALLER);
+
+ 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;
+}