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/* 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;
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;
}
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