base/SOURCES/0519-path-util-make-use-of-mnt_id-field-exported-in-proc-.patch

From f63b66b6347a8d8e5e6930a939d1997bfd8e2e7c Mon Sep 17 00:00:00 2001
From: Jan Synacek <jsynacek@redhat.com>
Date: Fri, 28 Jul 2017 15:31:50 +0200
Subject: [PATCH] path-util: make use of "mnt_id" field exported in
 /proc/self/fdinfo/<fd>

This commit is not a backport of a specific commit. It includes parts of
several upstream commits (3f72b427b44f39a1aec6806dad6f6b57103ae9ed,
5d409034017e9f9f8c4392157d95511fc2e05d87 and others).

The main goal was to bring path_is_mount_point() up to date, which meant
introducing fd_fdinfo_mnt_id() and fd_is_mount_point(). These were
needed mainly because we need to determine mount points based on
/proc/self/fdinfo/<fd> in containers. Also, there are more places in the
code where checks for mount points are performed, which would benefit from
this fix as well. Additionally, corresponding tests has been added.

Resolves: #1472439
---
 src/core/automount.c                        |   2 +-
 src/core/machine-id-setup.c                 |   2 +-
 src/core/mount-setup.c                      |   2 +-
 src/efi-boot-generator/efi-boot-generator.c |   2 +-
 src/gpt-auto-generator/gpt-auto-generator.c |   2 +-
 src/login/logind-user.c                     |   2 +-
 src/nspawn/nspawn.c                         |  10 +-
 src/shared/cgroup-util.c                    |   2 +-
 src/shared/condition.c                      |   2 +-
 src/shared/path-util.c                      | 209 +++++++++++++++-----
 src/shared/path-util.h                      |   3 +-
 src/test/test-path-util.c                   |  66 ++++++-
 12 files changed, 242 insertions(+), 62 deletions(-)

diff --git a/src/core/automount.c b/src/core/automount.c
index 4e066613d7..eedd9b8243 100644
--- a/src/core/automount.c
+++ b/src/core/automount.c
@@ -749,7 +749,7 @@ static int automount_start(Unit *u) {
         assert(a);
         assert(a->state == AUTOMOUNT_DEAD || a->state == AUTOMOUNT_FAILED);
 
-        if (path_is_mount_point(a->where, false)) {
+        if (path_is_mount_point(a->where, 0)) {
                 log_unit_error(u->id,
                                "Path %s is already a mount point, refusing start for %s",
                                a->where, u->id);
diff --git a/src/core/machine-id-setup.c b/src/core/machine-id-setup.c
index d00a53246f..1121d373fa 100644
--- a/src/core/machine-id-setup.c
+++ b/src/core/machine-id-setup.c
@@ -203,7 +203,7 @@ int machine_id_commit(const char *root) {
                 etc_machine_id = path_kill_slashes(x);
         }
 
-        r = path_is_mount_point(etc_machine_id, false);
+        r = path_is_mount_point(etc_machine_id, 0);
         if (r < 0)
                 return log_error_errno(r, "Failed to determine whether %s is a mount point: %m", etc_machine_id);
         if (r == 0) {
diff --git a/src/core/mount-setup.c b/src/core/mount-setup.c
index 521545e5ce..2b8fbab1a3 100644
--- a/src/core/mount-setup.c
+++ b/src/core/mount-setup.c
@@ -160,7 +160,7 @@ static int mount_one(const MountPoint *p, bool relabel) {
         if (relabel)
                 label_fix(p->where, true, true);
 
-        r = path_is_mount_point(p->where, true);
+        r = path_is_mount_point(p->where, AT_SYMLINK_FOLLOW);
         if (r < 0)
                 return r;
 
diff --git a/src/efi-boot-generator/efi-boot-generator.c b/src/efi-boot-generator/efi-boot-generator.c
index b3ff3a8b78..5492b19946 100644
--- a/src/efi-boot-generator/efi-boot-generator.c
+++ b/src/efi-boot-generator/efi-boot-generator.c
@@ -69,7 +69,7 @@ int main(int argc, char *argv[]) {
                 return EXIT_SUCCESS;
         }
 
-        if (path_is_mount_point("/boot", true) <= 0 &&
+        if (path_is_mount_point("/boot", AT_SYMLINK_FOLLOW) <= 0 &&
             dir_is_empty("/boot") <= 0) {
                 log_debug("/boot already populated, exiting.");
                 return EXIT_SUCCESS;
diff --git a/src/gpt-auto-generator/gpt-auto-generator.c b/src/gpt-auto-generator/gpt-auto-generator.c
index 00a2141a58..d7b047118d 100644
--- a/src/gpt-auto-generator/gpt-auto-generator.c
+++ b/src/gpt-auto-generator/gpt-auto-generator.c
@@ -299,7 +299,7 @@ static int probe_and_add_mount(
         assert(where);
         assert(description);
 
-        if (path_is_mount_point(where, true) <= 0 &&
+        if (path_is_mount_point(where, AT_SYMLINK_FOLLOW) <= 0 &&
             dir_is_empty(where) <= 0) {
                 log_debug("%s already populated, ignoring.", where);
                 return 0;
diff --git a/src/login/logind-user.c b/src/login/logind-user.c
index 4298704cea..912c50ebde 100644
--- a/src/login/logind-user.c
+++ b/src/login/logind-user.c
@@ -320,7 +320,7 @@ static int user_mkdir_runtime_path(User *u) {
         } else
                 p = u->runtime_path;
 
-        if (path_is_mount_point(p, false) <= 0) {
+        if (path_is_mount_point(p, 0) <= 0) {
                 _cleanup_free_ char *t = NULL;
 
                 (void) mkdir(p, 0700);
diff --git a/src/nspawn/nspawn.c b/src/nspawn/nspawn.c
index ea365b3f9b..a90a3a5d75 100644
--- a/src/nspawn/nspawn.c
+++ b/src/nspawn/nspawn.c
@@ -863,7 +863,7 @@ static int mount_all(const char *dest) {
                 if (!where)
                         return log_oom();
 
-                t = path_is_mount_point(where, true);
+                t = path_is_mount_point(where, AT_SYMLINK_FOLLOW);
                 if (t < 0) {
                         log_error_errno(t, "Failed to detect whether %s is a mount point: %m", where);
 
@@ -989,7 +989,7 @@ static int mount_cgroup_hierarchy(const char *dest, const char *controller, cons
 
         to = strjoina(dest, "/sys/fs/cgroup/", hierarchy);
 
-        r = path_is_mount_point(to, false);
+        r = path_is_mount_point(to, 0);
         if (r < 0)
                 return log_error_errno(r, "Failed to determine if %s is mounted already: %m", to);
         if (r > 0)
@@ -1787,7 +1787,7 @@ static int setup_journal(const char *directory) {
         if (!p || !q)
                 return log_oom();
 
-        if (path_is_mount_point(p, false) > 0) {
+        if (path_is_mount_point(p, 0) > 0) {
                 if (arg_link_journal != LINK_AUTO) {
                         log_error("%s: already a mount point, refusing to use for journal", p);
                         return -EEXIST;
@@ -1796,7 +1796,7 @@ static int setup_journal(const char *directory) {
                 return 0;
         }
 
-        if (path_is_mount_point(q, false) > 0) {
+        if (path_is_mount_point(q, 0) > 0) {
                 if (arg_link_journal != LINK_AUTO) {
                         log_error("%s: already a mount point, refusing to use for journal", q);
                         return -EEXIST;
@@ -3665,7 +3665,7 @@ int main(int argc, char *argv[]) {
                          * the specified is not a mount point we
                          * create the new snapshot in the parent
                          * directory, just next to it. */
-                        r = path_is_mount_point(arg_directory, false);
+                        r = path_is_mount_point(arg_directory, 0);
                         if (r < 0) {
                                 log_error_errno(r, "Failed to determine whether directory %s is mount point: %m", arg_directory);
                                 goto finish;
diff --git a/src/shared/cgroup-util.c b/src/shared/cgroup-util.c
index c5d9e4bb58..cf085cb5ff 100644
--- a/src/shared/cgroup-util.c
+++ b/src/shared/cgroup-util.c
@@ -488,7 +488,7 @@ int cg_get_path(const char *controller, const char *path, const char *suffix, ch
         if (_unlikely_(!good)) {
                 int r;
 
-                r = path_is_mount_point("/sys/fs/cgroup", false);
+                r = path_is_mount_point("/sys/fs/cgroup", 0);
                 if (r <= 0)
                         return r < 0 ? r : -ENOENT;
 
diff --git a/src/shared/condition.c b/src/shared/condition.c
index 796cc520d7..0d2cd2bc3a 100644
--- a/src/shared/condition.c
+++ b/src/shared/condition.c
@@ -350,7 +350,7 @@ static int condition_test_path_is_mount_point(Condition *c) {
         assert(c->parameter);
         assert(c->type == CONDITION_PATH_IS_MOUNT_POINT);
 
-        return path_is_mount_point(c->parameter, true) > 0;
+        return path_is_mount_point(c->parameter, AT_SYMLINK_FOLLOW) > 0;
 }
 
 static int condition_test_path_is_read_write(Condition *c) {
diff --git a/src/shared/path-util.c b/src/shared/path-util.c
index 1181ffb9d4..0f252ec262 100644
--- a/src/shared/path-util.c
+++ b/src/shared/path-util.c
@@ -36,6 +36,7 @@
 #include "strv.h"
 #include "path-util.h"
 #include "missing.h"
+#include "fileio.h"
 
 bool path_is_absolute(const char *p) {
         return p[0] == '/';
@@ -473,87 +474,203 @@ char* path_join(const char *root, const char *path, const char *rest) {
                                NULL);
 }
 
-int path_is_mount_point(const char *t, bool allow_symlink) {
+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;
+        }
 
-        union file_handle_union h = FILE_HANDLE_INIT;
+        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;
-        _cleanup_free_ char *parent = NULL;
+        bool nosupp = false, check_st_dev = true;
         struct stat a, b;
         int r;
-        bool nosupp = false;
 
-        /* We are not actually interested in the file handles, but
-         * name_to_handle_at() also passes us the mount ID, hence use
-         * it but throw the handle away */
+        assert(fd >= 0);
+        assert(filename);
 
-        if (path_equal(t, "/"))
-                return 1;
-
-        r = name_to_handle_at(AT_FDCWD, t, &h.handle, &mount_id, allow_symlink ? AT_SYMLINK_FOLLOW : 0);
+        /* 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 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 the traditional stat() logic. */
-                        goto fallback;
+                         * 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 fallback to the
+                         * 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 (errno == ENOENT)
-                        return 0;
                 else
                         return -errno;
         }
 
-        r = path_get_parent(t, &parent);
-        if (r < 0)
-                return r;
-
-        h.handle.handle_bytes = MAX_HANDLE_SZ;
-        r = name_to_handle_at(AT_FDCWD, parent, &h.handle, &mount_id_parent, AT_SYMLINK_FOLLOW);
-        if (r < 0)
-                if (errno == EOPNOTSUPP)
+        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;
+                                goto fallback_fdinfo;
                         else
-                                /* The parent can't do name_to_handle_at() but
-                                 * the directory we are interested in can?
-                                 * Or the other way around?
+                                /* 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
+                } else
                         return -errno;
-        else
-                return mount_id != mount_id_parent;
+        }
 
-fallback:
-        if (allow_symlink)
-                r = stat(t, &a);
-        else
-                r = lstat(t, &a);
+        /* 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 (r < 0) {
-                if (errno == ENOENT)
-                        return 0;
+        /* 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. */
 
-                return -errno;
-        }
+        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;
 
-        free(parent);
-        parent = NULL;
+        return mount_id != mount_id_parent;
 
-        r = path_get_parent(t, &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 = stat(parent, &b);
+        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 a.st_dev != b.st_dev;
+        return fd_is_mount_point(fd, basename(t), flags);
 }
 
 int path_is_read_only_fs(const char *path) {
diff --git a/src/shared/path-util.h b/src/shared/path-util.h
index 71bb740e98..e16484087f 100644
--- a/src/shared/path-util.h
+++ b/src/shared/path-util.h
@@ -53,7 +53,8 @@ char** path_strv_make_absolute_cwd(char **l);
 char** path_strv_resolve(char **l, const char *prefix);
 char** path_strv_resolve_uniq(char **l, const char *prefix);
 
-int path_is_mount_point(const char *path, bool allow_symlink);
+int fd_is_mount_point(int fd, const char *filename, int flags);
+int path_is_mount_point(const char *path, int flags);
 int path_is_read_only_fs(const char *path);
 int path_is_os_tree(const char *path);
 
diff --git a/src/test/test-path-util.c b/src/test/test-path-util.c
index 6396fcb398..8870f178a1 100644
--- a/src/test/test-path-util.c
+++ b/src/test/test-path-util.c
@@ -21,6 +21,7 @@
 
 #include <stdio.h>
 #include <unistd.h>
+#include <sys/mount.h>
 
 #include "path-util.h"
 #include "util.h"
@@ -85,8 +86,8 @@ static void test_path(void) {
         test_parent("/aa///file...", "/aa///");
         test_parent("file.../", NULL);
 
-        assert_se(path_is_mount_point("/", true));
-        assert_se(path_is_mount_point("/", false));
+        assert_se(path_is_mount_point("/", AT_SYMLINK_FOLLOW));
+        assert_se(path_is_mount_point("/", 0));
 
         {
                 char p1[] = "aaa/bbb////ccc";
@@ -99,6 +100,66 @@ static void test_path(void) {
         }
 }
 
+static void test_path_is_mount_point(void) {
+        int fd, rt, rf, rlt, rlf;
+        char tmp_dir[] = "/tmp/test-path-is-mount-point-XXXXXX";
+        _cleanup_free_ char *file1 = NULL, *file2 = NULL, *link1 = NULL, *link2 = NULL;
+
+        assert_se(path_is_mount_point("/", AT_SYMLINK_FOLLOW) > 0);
+        assert_se(path_is_mount_point("/", 0) > 0);
+
+        assert_se(path_is_mount_point("/proc", AT_SYMLINK_FOLLOW) > 0);
+        assert_se(path_is_mount_point("/proc", 0) > 0);
+
+        assert_se(path_is_mount_point("/proc/1", AT_SYMLINK_FOLLOW) == 0);
+        assert_se(path_is_mount_point("/proc/1", 0) == 0);
+
+        assert_se(path_is_mount_point("/sys", AT_SYMLINK_FOLLOW) > 0);
+        assert_se(path_is_mount_point("/sys", 0) > 0);
+
+        /* file mountpoints */
+        assert_se(mkdtemp(tmp_dir) != NULL);
+        file1 = path_join(NULL, tmp_dir, "file1");
+        assert_se(file1);
+        file2 = path_join(NULL, tmp_dir, "file2");
+        assert_se(file2);
+        fd = open(file1, O_WRONLY|O_CREAT|O_EXCL|O_CLOEXEC, 0664);
+        assert_se(fd > 0);
+        close(fd);
+        fd = open(file2, O_WRONLY|O_CREAT|O_EXCL|O_CLOEXEC, 0664);
+        assert_se(fd > 0);
+        close(fd);
+        link1 = path_join(NULL, tmp_dir, "link1");
+        assert_se(link1);
+        assert_se(symlink("file1", link1) == 0);
+        link2 = path_join(NULL, tmp_dir, "link2");
+        assert_se(link1);
+        assert_se(symlink("file2", link2) == 0);
+
+        assert_se(path_is_mount_point(file1, AT_SYMLINK_FOLLOW) == 0);
+        assert_se(path_is_mount_point(file1, 0) == 0);
+        assert_se(path_is_mount_point(link1, AT_SYMLINK_FOLLOW) == 0);
+        assert_se(path_is_mount_point(link1, 0) == 0);
+
+        /* this test will only work as root */
+        if (mount(file1, file2, NULL, MS_BIND, NULL) >= 0) {
+                rf = path_is_mount_point(file2, 0);
+                rt = path_is_mount_point(file2, AT_SYMLINK_FOLLOW);
+                rlf = path_is_mount_point(link2, 0);
+                rlt = path_is_mount_point(link2, AT_SYMLINK_FOLLOW);
+
+                assert_se(umount(file2) == 0);
+
+                assert_se(rf == 1);
+                assert_se(rt == 1);
+                assert_se(rlf == 0);
+                assert_se(rlt == 1);
+        } else
+                printf("Skipping bind mount file test: %m\n");
+
+        assert_se(rm_rf(tmp_dir, false, true, false) == 0);
+}
+
 static void test_find_binary(const char *self, bool local) {
         char *p;
 
@@ -288,6 +349,7 @@ int main(int argc, char **argv) {
         test_make_relative();
         test_strv_resolve();
         test_path_startswith();
+        test_path_is_mount_point();
 
         return 0;
 }