Merge pull request #3920 from brauner/2021-08-02.fixes

mount_utils: introduce mount_at()

src/lxc/conf.c

@@ -1089,7 +1089,7 @@ static int lxc_allocate_ttys(struct lxc_conf *conf)
 
 void lxc_delete_tty(struct lxc_tty_info *ttys)
 {
-	if (!ttys->tty)
+	if (!ttys || !ttys->tty)
 		return;
 
 	for (int i = 0; i < ttys->max; i++) {
@@ -1742,7 +1742,9 @@ static int lxc_setup_devpts_child(struct lxc_handler *handler)
 
 		for (ret = -1, opts = mntopt_sets; opts && *opts; opts++) {
 			/* mount new devpts instance */
-			ret = mount_beneath_fd(rootfs->dfd_dev, "", "pts", "devpts", MS_NOSUID | MS_NOEXEC, *opts);
+			ret = mount_at(rootfs->dfd_dev, "", 0,
+				       rootfs->dfd_dev, "pts", PROTECT_LOOKUP_BENEATH,
+				       "devpts", MS_NOSUID | MS_NOEXEC, *opts);
 			if (ret == 0)
 				break;
 		}
@@ -1775,7 +1777,9 @@ static int lxc_setup_devpts_child(struct lxc_handler *handler)
 	DEBUG("Created \"/dev/ptmx\" file as bind mount target");
 
 	/* Main option: use a bind-mount to please AppArmor  */
-	ret = mount_beneath_fd(rootfs->dfd_dev, "pts/ptmx", "ptmx", NULL, MS_BIND, NULL);
+	ret = mount_at(rootfs->dfd_dev, "pts/ptmx", (PROTECT_LOOKUP_BENEATH_WITH_SYMLINKS & ~RESOLVE_NO_XDEV),
+		       rootfs->dfd_dev, "ptmx", (PROTECT_LOOKUP_BENEATH_WITH_SYMLINKS & ~RESOLVE_NO_XDEV),
+		       NULL, MS_BIND, NULL);
 	if (!ret)
 		return log_debug(0, "Bind mounted \"/dev/pts/ptmx\" to \"/dev/ptmx\"");
 	else
@@ -3026,7 +3030,7 @@ static int lxc_idmapped_mounts_child(struct lxc_handler *handler)
 out:
 	ret = lxc_abstract_unix_send_credential(handler->data_sock[0], NULL, 0);
 	if (ret < 0)
-		return syserror("Failed to inform child that we are done setting up mounts");
+		return syserror("Failed to inform parent that we are done setting up mounts");
 
 	return fret;
 }
@@ -4055,40 +4059,45 @@ int lxc_idmapped_mounts_parent(struct lxc_handler *handler)
 
 static int lxc_recv_ttys_from_child(struct lxc_handler *handler)
 {
-	int i;
-	struct lxc_terminal_info *tty;
-	int ret = -1;
+	call_cleaner(lxc_delete_tty) struct lxc_tty_info *info_new = &(struct lxc_tty_info){};
 	int sock = handler->data_sock[1];
 	struct lxc_conf *conf = handler->conf;
-	struct lxc_tty_info *ttys = &conf->ttys;
+	struct lxc_tty_info *tty_info = &conf->ttys;
+	size_t ttys_max = tty_info->max;
+	struct lxc_terminal_info *terminal_info;
+	int ret;
 
-	if (!conf->ttys.max)
+	if (!ttys_max)
 		return 0;
 
-	ttys->tty = malloc(sizeof(*ttys->tty) * ttys->max);
-	if (!ttys->tty)
-		return -1;
+	info_new->tty = malloc(sizeof(*(info_new->tty)) * ttys_max);
+	if (!info_new->tty)
+		return ret_errno(ENOMEM);
 
-	for (i = 0; i < conf->ttys.max; i++) {
-		int ttyx = -EBADF, ttyy = -EBADF;
-
-		ret = lxc_abstract_unix_recv_two_fds(sock, &ttyx, &ttyy);
-		if (ret < 0)
-			break;
-
-		tty = &ttys->tty[i];
-		tty->busy = -1;
-		tty->ptx = ttyx;
-		tty->pty = ttyy;
-		TRACE("Received pty with ptx fd %d and pty fd %d from child", tty->ptx, tty->pty);
+	for (int i = 0; i < ttys_max; i++) {
+		terminal_info = &info_new->tty[i];
+		terminal_info->busy = -1;
+		terminal_info->ptx = -EBADF;
+		terminal_info->pty = -EBADF;
 	}
 
-	if (ret < 0)
-		SYSERROR("Failed to receive %zu ttys from child", ttys->max);
-	else
-		TRACE("Received %zu ttys from child", ttys->max);
+	for (int i = 0; i < ttys_max; i++) {
+		int ptx = -EBADF, pty = -EBADF;
 
-	return ret;
+		ret = lxc_abstract_unix_recv_two_fds(sock, &ptx, &pty);
+		if (ret < 0)
+			return syserror("Failed to receive %zu ttys from child", ttys_max);
+
+		terminal_info = &info_new->tty[i];
+		terminal_info->ptx = ptx;
+		terminal_info->pty = pty;
+		TRACE("Received pty with ptx fd %d and pty fd %d from child",
+		      terminal_info->ptx, terminal_info->pty);
+	}
+
+	tty_info->tty = move_ptr(info_new->tty);
+	TRACE("Received %zu ttys from child", ttys_max);
+	return 0;
 }
 
 static int lxc_send_console_to_parent(struct lxc_handler *handler)

src/lxc/mount_utils.c

@@ -606,66 +606,56 @@ bool can_use_bind_mounts(void)
 	return supported == 1;
 }
 
-int mount_beneath_fd(int fd, const char *source, const char *target,
-		     const char *fs_name, unsigned int flags, const void *data)
+int mount_at(int dfd_from, const char *path_from, __u64 resolve_flags_from,
+	     int dfd_to, const char *path_to, __u64 resolve_flags_to,
+	     const char *fs_name, unsigned int flags, const void *data)
 {
-	int ret;
-	char buf_source[PATH_MAX], buf_target[PATH_MAX];
+	__do_close int __fd_from = -EBADF, __fd_to = -EBADF;
+	char *from = NULL, *to = NULL;
+	int fd_from, fd_to, ret;
+	char buf_from[LXC_PROC_SELF_FD_LEN], buf_to[LXC_PROC_SELF_FD_LEN];
 
-	if (abspath(source) || abspath(target))
+	if (dfd_from < 0 && !abspath(path_from))
 		return ret_errno(EINVAL);
 
-	ret = strnprintf(buf_target, sizeof(buf_target), "/proc/self/fd/%d/%s", fd, target);
-	if (ret < 0)
-		return syserror("Failed to create path");
+	if (dfd_to < 0 && !abspath(path_to))
+		return ret_errno(EINVAL);
 
-	if (is_empty_string(source)) {
-		ret = mount(fs_name ?: "", buf_target, fs_name, flags, data);
+	if (!is_empty_string(path_from)) {
+		__fd_from = open_at(dfd_from, path_from, PROTECT_OPATH_FILE, resolve_flags_from, 0);
+		if (__fd_from < 0)
+			return -errno;
+		fd_from = __fd_from;
 	} else {
-		ret = strnprintf(buf_source, sizeof(buf_source), "/proc/self/fd/%d/%s", fd, source);
+		fd_from = dfd_from;
+	}
+	if (fd_from >= 0) {
+		ret = strnprintf(buf_from, sizeof(buf_from), "/proc/self/fd/%d", fd_from);
 		if (ret < 0)
 			return syserror("Failed to create path");
-
-		source = buf_source;
-		ret = mount(source, buf_target, fs_name, flags, data);
+		from = buf_from;
 	}
-	if (ret < 0)
-		return syserror("Failed to mount \"%s\" to \"%s\"", source, buf_target);
 
-	TRACE("Mounted \"%s\" to \"%s\"", source, buf_target);
-	return 0;
-}
-
-int mount_fd(int fd_source, int fd_target, const char *fs_name,
-	     unsigned int flags, const void *data)
-{
-	int ret;
-	char buf_source[LXC_PROC_PID_FD_LEN], buf_target[LXC_PROC_PID_FD_LEN];
-	char *source = buf_source, *target = buf_target;
-
-	if (fd_source < 0) {
-		source = NULL;
+	if (!is_empty_string(path_to)) {
+		__fd_to = open_at(dfd_to, path_to, PROTECT_OPATH_FILE, resolve_flags_to, 0);
+		if (__fd_to < 0)
+			return -errno;
+		fd_to = __fd_to;
 	} else {
-		ret = strnprintf(buf_source, sizeof(buf_source),
-				 "/proc/self/fd/%d", fd_source);
+		fd_to = dfd_to;
+	}
+	if (fd_to >= 0) {
+		ret = strnprintf(buf_to, sizeof(buf_to), "/proc/self/fd/%d", fd_to);
 		if (ret < 0)
-			return ret;
+			return syserror("Failed to create path");
+		to = buf_to;
 	}
 
-	if (fd_target < 0) {
-		target = NULL;
-	} else {
-		ret = strnprintf(buf_target, sizeof(buf_target),
-				 "/proc/self/fd/%d", fd_target);
-		if (ret < 0)
-			return ret;
-	}
-
-	ret = mount(source, target, "none", MS_BIND, 0);
+	ret = mount(from ?: fs_name, to, fs_name, flags, data);
 	if (ret < 0)
 		return syserror("Failed to mount \"%s\" to \"%s\"",
-				maybe_empty(source), maybe_empty(target));
+				maybe_empty(from), maybe_empty(to));
 
-	TRACE("Mounted \"%s\" to \"%s\"", maybe_empty(source), maybe_empty(target));
+	TRACE("Mounted \"%s\" to \"%s\"", maybe_empty(from), maybe_empty(to));
 	return 0;
 }

src/lxc/mount_utils.h

@@ -221,10 +221,15 @@ __hidden extern unsigned long add_required_remount_flags(const char *s,
 
 __hidden extern bool can_use_mount_api(void);
 __hidden extern bool can_use_bind_mounts(void);
-__hidden extern int mount_beneath_fd(int fd, const char *source,
-				     const char *target, const char *fs_name,
-				     unsigned int flags, const void *data);
-__hidden extern int mount_fd(int fd_source, int fd_target, const char *fs_name,
-			     unsigned int flags, const void *data);
+__hidden extern int mount_at(int dfd_from, const char *path_from,
+			     __u64 resolve_flags_from, int dfd_to,
+			     const char *path_to, __u64 resolve_flags_to,
+			     const char *fs_name, unsigned int flags,
+			     const void *data);
+static inline int mount_fd(int fd_from, int fd_to, const char *fs_name,
+			   unsigned int flags, const void *data)
+{
+	return mount_at(fd_from, "", 0, fd_to, "", 0, fs_name, flags, data);
+}
 
 #endif /* __LXC_MOUNT_UTILS_H */