Adding upstream version 241.upstream/241upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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
index 0000000..1e946a0
--- /dev/null
+++ 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;
+}