path: root/debian/patches/machine-basic-factor-out-helper-function-to-add-airlocked.patch

From: Luca Boccassi <luca.boccassi@microsoft.com>
Date: Thu, 13 Aug 2020 14:01:34 +0100
Subject: machine/basic: factor out helper function to add airlocked mount to
 namespace

(cherry picked from commit 6af52c3a458691b016bedeba34c1e72294a67c81)
---
 src/machine/machine-dbus.c | 214 ++------------------------------------------
 src/shared/mount-util.c    | 217 +++++++++++++++++++++++++++++++++++++++++++++
 src/shared/mount-util.h    |   2 +
 3 files changed, 227 insertions(+), 206 deletions(-)

diff --git a/src/machine/machine-dbus.c b/src/machine/machine-dbus.c
index 1105008..3c8f4fd 100644
--- a/src/machine/machine-dbus.c
+++ b/src/machine/machine-dbus.c
@@ -810,17 +810,9 @@ int bus_machine_method_open_shell(sd_bus_message *message, void *userdata, sd_bu
 }
 
 int bus_machine_method_bind_mount(sd_bus_message *message, void *userdata, sd_bus_error *error) {
-        _cleanup_close_pair_ int errno_pipe_fd[2] = { -1, -1 };
-        char mount_slave[] = "/tmp/propagate.XXXXXX", *mount_tmp, *mount_outside, *p;
-        bool mount_slave_created = false, mount_slave_mounted = false,
-                mount_tmp_created = false, mount_tmp_mounted = false,
-                mount_outside_created = false, mount_outside_mounted = false;
-        _cleanup_free_ char *chased_src = NULL;
         int read_only, make_file_or_directory;
-        const char *dest, *src;
+        const char *dest, *src, *propagate_directory;
         Machine *m = userdata;
-        struct stat st;
-        pid_t child;
         uid_t uid;
         int r;
 
@@ -862,205 +854,15 @@ int bus_machine_method_bind_mount(sd_bus_message *message, void *userdata, sd_bu
         if (uid != 0)
                 return sd_bus_error_setf(error, SD_BUS_ERROR_NOT_SUPPORTED, "Can't bind mount on container with user namespacing applied.");
 
-        /* One day, when bind mounting /proc/self/fd/n works across
-         * namespace boundaries we should rework this logic to make
-         * use of it... */
-
-        p = strjoina("/run/systemd/nspawn/propagate/", m->name, "/");
-        if (laccess(p, F_OK) < 0)
-                return sd_bus_error_setf(error, SD_BUS_ERROR_NOT_SUPPORTED, "Container does not allow propagation of mount points.");
-
-        r = chase_symlinks(src, NULL, CHASE_TRAIL_SLASH, &chased_src, NULL);
+        propagate_directory = strjoina("/run/systemd/nspawn/propagate/", m->name);
+        r = bind_mount_in_namespace(m->leader,
+                                    propagate_directory,
+                                    "/run/host/incoming/",
+                                    src, dest, read_only, make_file_or_directory);
         if (r < 0)
-                return sd_bus_error_set_errnof(error, r, "Failed to resolve source path: %m");
-
-        if (lstat(chased_src, &st) < 0)
-                return sd_bus_error_set_errnof(error, errno, "Failed to stat() source path: %m");
-        if (S_ISLNK(st.st_mode)) /* This shouldn't really happen, given that we just chased the symlinks above, but let's better be safe… */
-                return sd_bus_error_setf(error, SD_BUS_ERROR_NOT_SUPPORTED, "Source directory can't be a symbolic link");
-
-        /* Our goal is to install a new bind mount into the container,
-           possibly read-only. This is irritatingly complex
-           unfortunately, currently.
-
-           First, we start by creating a private playground in /tmp,
-           that we can mount MS_SLAVE. (Which is necessary, since
-           MS_MOVE cannot be applied to mounts with MS_SHARED parent
-           mounts.) */
-
-        if (!mkdtemp(mount_slave))
-                return sd_bus_error_set_errnof(error, errno, "Failed to create playground %s: %m", mount_slave);
-
-        mount_slave_created = true;
-
-        r = mount_nofollow_verbose(LOG_DEBUG, mount_slave, mount_slave, NULL, MS_BIND, NULL);
-        if (r < 0) {
-                sd_bus_error_set_errnof(error, r, "Failed to make bind mount %s: %m", mount_slave);
-                goto finish;
-        }
-
-        mount_slave_mounted = true;
-
-        r = mount_nofollow_verbose(LOG_DEBUG, NULL, mount_slave, NULL, MS_SLAVE, NULL);
-        if (r < 0) {
-                sd_bus_error_set_errnof(error, r, "Failed to remount slave %s: %m", mount_slave);
-                goto finish;
-        }
-
-        /* Second, we mount the source file or directory to a directory inside of our MS_SLAVE playground. */
-        mount_tmp = strjoina(mount_slave, "/mount");
-        r = make_mount_point_inode_from_stat(&st, mount_tmp, 0700);
-        if (r < 0) {
-                sd_bus_error_set_errnof(error, r, "Failed to create temporary mount point %s: %m", mount_tmp);
-                goto finish;
-        }
-
-        mount_tmp_created = true;
-
-        r = mount_nofollow_verbose(LOG_DEBUG, chased_src, mount_tmp, NULL, MS_BIND, NULL);
-        if (r < 0) {
-                sd_bus_error_set_errnof(error, r, "Failed to mount %s: %m", chased_src);
-                goto finish;
-        }
-
-        mount_tmp_mounted = true;
-
-        /* Third, we remount the new bind mount read-only if requested. */
-        if (read_only) {
-                r = mount_nofollow_verbose(LOG_DEBUG, NULL, mount_tmp, NULL, MS_BIND|MS_REMOUNT|MS_RDONLY, NULL);
-                if (r < 0) {
-                        sd_bus_error_set_errnof(error, r, "Failed to remount read-only %s: %m", mount_tmp);
-                        goto finish;
-                }
-        }
-
-        /* Fourth, we move the new bind mount into the propagation directory. This way it will appear there read-only
-         * right-away. */
-
-        mount_outside = strjoina("/run/systemd/nspawn/propagate/", m->name, "/XXXXXX");
-        if (S_ISDIR(st.st_mode))
-                r = mkdtemp(mount_outside) ? 0 : -errno;
-        else {
-                r = mkostemp_safe(mount_outside);
-                safe_close(r);
-        }
-        if (r < 0) {
-                sd_bus_error_set_errnof(error, r, "Cannot create propagation file or directory %s: %m", mount_outside);
-                goto finish;
-        }
-
-        mount_outside_created = true;
-
-        r = mount_nofollow_verbose(LOG_DEBUG, mount_tmp, mount_outside, NULL, MS_MOVE, NULL);
-        if (r < 0) {
-                sd_bus_error_set_errnof(error, r, "Failed to move %s to %s: %m", mount_tmp, mount_outside);
-                goto finish;
-        }
-
-        mount_outside_mounted = true;
-        mount_tmp_mounted = false;
-
-        if (S_ISDIR(st.st_mode))
-                (void) rmdir(mount_tmp);
-        else
-                (void) unlink(mount_tmp);
-        mount_tmp_created = false;
-
-        (void) umount_verbose(LOG_DEBUG, mount_slave, UMOUNT_NOFOLLOW);
-        mount_slave_mounted = false;
-
-        (void) rmdir(mount_slave);
-        mount_slave_created = false;
-
-        if (pipe2(errno_pipe_fd, O_CLOEXEC|O_NONBLOCK) < 0) {
-                r = sd_bus_error_set_errnof(error, errno, "Failed to create pipe: %m");
-                goto finish;
-        }
-
-        r = safe_fork("(sd-bindmnt)", FORK_RESET_SIGNALS, &child);
-        if (r < 0) {
-                sd_bus_error_set_errnof(error, r, "Failed to fork(): %m");
-                goto finish;
-        }
-        if (r == 0) {
-                const char *mount_inside, *q;
-                int mntfd;
-
-                errno_pipe_fd[0] = safe_close(errno_pipe_fd[0]);
-
-                q = procfs_file_alloca(m->leader, "ns/mnt");
-                mntfd = open(q, O_RDONLY|O_NOCTTY|O_CLOEXEC);
-                if (mntfd < 0) {
-                        r = log_error_errno(errno, "Failed to open mount namespace of leader: %m");
-                        goto child_fail;
-                }
-
-                if (setns(mntfd, CLONE_NEWNS) < 0) {
-                        r = log_error_errno(errno, "Failed to join namespace of leader: %m");
-                        goto child_fail;
-                }
-
-                if (make_file_or_directory) {
-                        (void) mkdir_parents(dest, 0755);
-                        (void) make_mount_point_inode_from_stat(&st, dest, 0700);
-                }
-
-                mount_inside = strjoina("/run/host/incoming/", basename(mount_outside));
-                r = mount_nofollow_verbose(LOG_ERR, mount_inside, dest, NULL, MS_MOVE, NULL);
-                if (r < 0)
-                        goto child_fail;
-
-                _exit(EXIT_SUCCESS);
-
-        child_fail:
-                (void) write(errno_pipe_fd[1], &r, sizeof(r));
-                errno_pipe_fd[1] = safe_close(errno_pipe_fd[1]);
-
-                _exit(EXIT_FAILURE);
-        }
-
-        errno_pipe_fd[1] = safe_close(errno_pipe_fd[1]);
+                return sd_bus_error_set_errnof(error, r, "Failed to mount %s on %s in machine's namespace: %m", src, dest);
 
-        r = wait_for_terminate_and_check("(sd-bindmnt)", child, 0);
-        if (r < 0) {
-                r = sd_bus_error_set_errnof(error, r, "Failed to wait for child: %m");
-                goto finish;
-        }
-        if (r != EXIT_SUCCESS) {
-                if (read(errno_pipe_fd[0], &r, sizeof(r)) == sizeof(r))
-                        r = sd_bus_error_set_errnof(error, r, "Failed to mount: %m");
-                else
-                        r = sd_bus_error_setf(error, SD_BUS_ERROR_FAILED, "Child failed.");
-                goto finish;
-        }
-
-        r = sd_bus_reply_method_return(message, NULL);
-
-finish:
-        if (mount_outside_mounted)
-                (void) umount_verbose(LOG_DEBUG, mount_outside, UMOUNT_NOFOLLOW);
-        if (mount_outside_created) {
-                if (S_ISDIR(st.st_mode))
-                        (void) rmdir(mount_outside);
-                else
-                        (void) unlink(mount_outside);
-        }
-
-        if (mount_tmp_mounted)
-                (void) umount_verbose(LOG_DEBUG, mount_tmp, UMOUNT_NOFOLLOW);
-        if (mount_tmp_created) {
-                if (S_ISDIR(st.st_mode))
-                        (void) rmdir(mount_tmp);
-                else
-                        (void) unlink(mount_tmp);
-        }
-
-        if (mount_slave_mounted)
-                (void) umount_verbose(LOG_DEBUG, mount_slave, UMOUNT_NOFOLLOW);
-        if (mount_slave_created)
-                (void) rmdir(mount_slave);
-
-        return r;
+        return sd_bus_reply_method_return(message, NULL);
 }
 
 int bus_machine_method_copy(sd_bus_message *message, void *userdata, sd_bus_error *error) {
diff --git a/src/shared/mount-util.c b/src/shared/mount-util.c
index b19b384..4cfbb55 100644
--- a/src/shared/mount-util.c
+++ b/src/shared/mount-util.c
@@ -14,15 +14,18 @@
 #include "fs-util.h"
 #include "hashmap.h"
 #include "libmount-util.h"
+#include "mkdir.h"
 #include "mount-util.h"
 #include "mountpoint-util.h"
 #include "parse-util.h"
 #include "path-util.h"
+#include "process-util.h"
 #include "set.h"
 #include "stat-util.h"
 #include "stdio-util.h"
 #include "string-util.h"
 #include "strv.h"
+#include "tmpfile-util.h"
 
 int mount_fd(const char *source,
              int target_fd,
@@ -742,3 +745,217 @@ int mount_option_mangle(
 
         return 0;
 }
+
+int bind_mount_in_namespace(
+                pid_t target,
+                const char *propagate_path,
+                const char *incoming_path,
+                const char *src,
+                const char *dest,
+                bool read_only,
+                bool make_file_or_directory) {
+
+        _cleanup_close_pair_ int errno_pipe_fd[2] = { -1, -1 };
+        char mount_slave[] = "/tmp/propagate.XXXXXX", *mount_tmp, *mount_outside, *p;
+        bool mount_slave_created = false, mount_slave_mounted = false,
+                mount_tmp_created = false, mount_tmp_mounted = false,
+                mount_outside_created = false, mount_outside_mounted = false;
+        _cleanup_free_ char *chased_src = NULL;
+        struct stat st;
+        pid_t child;
+        int r;
+
+        assert(target > 0);
+        assert(propagate_path);
+        assert(incoming_path);
+        assert(src);
+        assert(dest);
+
+        /* One day, when bind mounting /proc/self/fd/n works across
+         * namespace boundaries we should rework this logic to make
+         * use of it... */
+
+        p = strjoina(propagate_path, "/");
+        r = laccess(p, F_OK);
+        if (r < 0)
+                return log_debug_errno(r == -ENOENT ? SYNTHETIC_ERRNO(EOPNOTSUPP) : r, "Target does not allow propagation of mount points");
+
+        r = chase_symlinks(src, NULL, CHASE_TRAIL_SLASH, &chased_src, NULL);
+        if (r < 0)
+                return log_debug_errno(r, "Failed to resolve source path of %s: %m", src);
+
+        if (lstat(chased_src, &st) < 0)
+                return log_debug_errno(errno, "Failed to stat() resolved source path %s: %m", chased_src);
+        if (S_ISLNK(st.st_mode)) /* This shouldn't really happen, given that we just chased the symlinks above, but let's better be safe… */
+                return log_debug_errno(SYNTHETIC_ERRNO(EOPNOTSUPP), "Source directory %s can't be a symbolic link", chased_src);
+
+        /* Our goal is to install a new bind mount into the container,
+           possibly read-only. This is irritatingly complex
+           unfortunately, currently.
+
+           First, we start by creating a private playground in /tmp,
+           that we can mount MS_SLAVE. (Which is necessary, since
+           MS_MOVE cannot be applied to mounts with MS_SHARED parent
+           mounts.) */
+
+        if (!mkdtemp(mount_slave))
+                return log_debug_errno(errno, "Failed to create playground %s: %m", mount_slave);
+
+        mount_slave_created = true;
+
+        r = mount_nofollow_verbose(LOG_DEBUG, mount_slave, mount_slave, NULL, MS_BIND, NULL);
+        if (r < 0)
+                goto finish;
+
+        mount_slave_mounted = true;
+
+        r = mount_nofollow_verbose(LOG_DEBUG, NULL, mount_slave, NULL, MS_SLAVE, NULL);
+        if (r < 0)
+                goto finish;
+
+        /* Second, we mount the source file or directory to a directory inside of our MS_SLAVE playground. */
+        mount_tmp = strjoina(mount_slave, "/mount");
+        r = make_mount_point_inode_from_stat(&st, mount_tmp, 0700);
+        if (r < 0) {
+                log_debug_errno(r, "Failed to create temporary mount point %s: %m", mount_tmp);
+                goto finish;
+        }
+
+        mount_tmp_created = true;
+
+        r = mount_nofollow_verbose(LOG_DEBUG, chased_src, mount_tmp, NULL, MS_BIND, NULL);
+        if (r < 0)
+                goto finish;
+
+        mount_tmp_mounted = true;
+
+        /* Third, we remount the new bind mount read-only if requested. */
+        if (read_only) {
+                r = mount_nofollow_verbose(LOG_DEBUG, NULL, mount_tmp, NULL, MS_BIND|MS_REMOUNT|MS_RDONLY, NULL);
+                if (r < 0)
+                        goto finish;
+        }
+
+        /* Fourth, we move the new bind mount into the propagation directory. This way it will appear there read-only
+         * right-away. */
+
+        mount_outside = strjoina(propagate_path, "/XXXXXX");
+        if (S_ISDIR(st.st_mode))
+                r = mkdtemp(mount_outside) ? 0 : -errno;
+        else {
+                r = mkostemp_safe(mount_outside);
+                safe_close(r);
+        }
+        if (r < 0) {
+                log_debug_errno(r, "Cannot create propagation file or directory %s: %m", mount_outside);
+                goto finish;
+        }
+
+        mount_outside_created = true;
+
+        r = mount_nofollow_verbose(LOG_DEBUG, mount_tmp, mount_outside, NULL, MS_MOVE, NULL);
+        if (r < 0)
+                goto finish;
+
+        mount_outside_mounted = true;
+        mount_tmp_mounted = false;
+
+        if (S_ISDIR(st.st_mode))
+                (void) rmdir(mount_tmp);
+        else
+                (void) unlink(mount_tmp);
+        mount_tmp_created = false;
+
+        (void) umount_verbose(LOG_DEBUG, mount_slave, UMOUNT_NOFOLLOW);
+        mount_slave_mounted = false;
+
+        (void) rmdir(mount_slave);
+        mount_slave_created = false;
+
+        if (pipe2(errno_pipe_fd, O_CLOEXEC|O_NONBLOCK) < 0) {
+                log_debug_errno(errno, "Failed to create pipe: %m");
+                goto finish;
+        }
+
+        r = safe_fork("(sd-bindmnt)", FORK_RESET_SIGNALS, &child);
+        if (r < 0)
+                goto finish;
+        if (r == 0) {
+                const char *mount_inside, *q;
+                int mntfd;
+
+                errno_pipe_fd[0] = safe_close(errno_pipe_fd[0]);
+
+                q = procfs_file_alloca(target, "ns/mnt");
+                mntfd = open(q, O_RDONLY|O_NOCTTY|O_CLOEXEC);
+                if (mntfd < 0) {
+                        r = log_error_errno(errno, "Failed to open mount namespace of leader: %m");
+                        goto child_fail;
+                }
+
+                if (setns(mntfd, CLONE_NEWNS) < 0) {
+                        r = log_error_errno(errno, "Failed to join namespace of leader: %m");
+                        goto child_fail;
+                }
+
+                if (make_file_or_directory) {
+                        (void) mkdir_parents(dest, 0755);
+                        (void) make_mount_point_inode_from_stat(&st, dest, 0700);
+                }
+
+                /* Fifth, move the mount to the right place inside */
+                mount_inside = strjoina(incoming_path, basename(mount_outside));
+                r = mount_nofollow_verbose(LOG_ERR, mount_inside, dest, NULL, MS_MOVE, NULL);
+                if (r < 0)
+                        goto child_fail;
+
+                _exit(EXIT_SUCCESS);
+
+        child_fail:
+                (void) write(errno_pipe_fd[1], &r, sizeof(r));
+                errno_pipe_fd[1] = safe_close(errno_pipe_fd[1]);
+
+                _exit(EXIT_FAILURE);
+        }
+
+        errno_pipe_fd[1] = safe_close(errno_pipe_fd[1]);
+
+        r = wait_for_terminate_and_check("(sd-bindmnt)", child, 0);
+        if (r < 0) {
+                log_debug_errno(r, "Failed to wait for child: %m");
+                goto finish;
+        }
+        if (r != EXIT_SUCCESS) {
+                if (read(errno_pipe_fd[0], &r, sizeof(r)) == sizeof(r))
+                        log_debug_errno(r, "Failed to mount: %m");
+                else
+                        log_debug("Child failed.");
+                goto finish;
+        }
+
+finish:
+        if (mount_outside_mounted)
+                (void) umount_verbose(LOG_DEBUG, mount_outside, UMOUNT_NOFOLLOW);
+        if (mount_outside_created) {
+                if (S_ISDIR(st.st_mode))
+                        (void) rmdir(mount_outside);
+                else
+                        (void) unlink(mount_outside);
+        }
+
+        if (mount_tmp_mounted)
+                (void) umount_verbose(LOG_DEBUG, mount_tmp, UMOUNT_NOFOLLOW);
+        if (mount_tmp_created) {
+                if (S_ISDIR(st.st_mode))
+                        (void) rmdir(mount_tmp);
+                else
+                        (void) unlink(mount_tmp);
+        }
+
+        if (mount_slave_mounted)
+                (void) umount_verbose(LOG_DEBUG, mount_slave, UMOUNT_NOFOLLOW);
+        if (mount_slave_created)
+                (void) rmdir(mount_slave);
+
+        return r;
+}
diff --git a/src/shared/mount-util.h b/src/shared/mount-util.h
index 6202008..c3500a0 100644
--- a/src/shared/mount-util.h
+++ b/src/shared/mount-util.h
@@ -97,3 +97,5 @@ static inline char* umount_and_rmdir_and_free(char *p) {
         return NULL;
 }
 DEFINE_TRIVIAL_CLEANUP_FUNC(char*, umount_and_rmdir_and_free);
+
+int bind_mount_in_namespace(pid_t target, const char *propagate_path, const char *incoming_path, const char *src, const char *dest, bool read_only, bool make_file_or_directory);