machined: add new call OpenMachineLogin() that starts a getty in a container on a pty and returns the pty master fd to the client

This is a one-stop solution for "machinectl login", and should simplify
getting logins in containers.

src/machine/machine-dbus.c

@@ -32,6 +32,8 @@
 #include "fileio.h"
 #include "in-addr-util.h"
 #include "local-addresses.h"
+#include "path-util.h"
+#include "bus-internal.h"
 #include "machine.h"
 
 static int property_get_id(
@@ -391,94 +393,19 @@ int bus_machine_method_get_os_release(sd_bus *bus, sd_bus_message *message, void
 }
 
 int bus_machine_method_open_pty(sd_bus *bus, sd_bus_message *message, void *userdata, sd_bus_error *error) {
-        _cleanup_close_ int pidnsfd = -1, mntnsfd = -1, rootfd = -1;
         _cleanup_bus_message_unref_ sd_bus_message *reply = NULL;
-        _cleanup_close_pair_ int pair[2] = { -1, -1 };
-        _cleanup_close_ int master = -1;
-        union {
-                struct cmsghdr cmsghdr;
-                uint8_t buf[CMSG_SPACE(sizeof(int))];
-        } control = {};
-        struct msghdr mh = {
-                .msg_control = &control,
-                .msg_controllen = sizeof(control),
-        };
-        Machine *m = userdata;
         _cleanup_free_ char *pty_name = NULL;
-        struct cmsghdr *cmsg;
-        siginfo_t si;
-        pid_t child;
+        _cleanup_close_ int master = -1;
+        Machine *m = userdata;
         int r;
 
         assert(bus);
         assert(message);
         assert(m);
 
-        r = namespace_open(m->leader, &pidnsfd, &mntnsfd, NULL, &rootfd);
-        if (r < 0)
-                return r;
-
-        if (socketpair(AF_UNIX, SOCK_DGRAM, 0, pair) < 0)
-                return -errno;
-
-        child = fork();
-        if (child < 0)
-                return -errno;
-
-        if (child == 0) {
-                pair[0] = safe_close(pair[0]);
-
-                r = namespace_enter(pidnsfd, mntnsfd, -1, rootfd);
-                if (r < 0)
-                        _exit(EXIT_FAILURE);
-
-                master = posix_openpt(O_RDWR|O_NOCTTY|O_CLOEXEC);
-                if (master < 0)
-                        _exit(EXIT_FAILURE);
-
-                cmsg = CMSG_FIRSTHDR(&mh);
-                cmsg->cmsg_level = SOL_SOCKET;
-                cmsg->cmsg_type = SCM_RIGHTS;
-                cmsg->cmsg_len = CMSG_LEN(sizeof(int));
-                memcpy(CMSG_DATA(cmsg), &master, sizeof(int));
-
-                mh.msg_controllen = cmsg->cmsg_len;
-
-                if (sendmsg(pair[1], &mh, MSG_NOSIGNAL) < 0)
-                        _exit(EXIT_FAILURE);
-
-                _exit(EXIT_SUCCESS);
-        }
-
-        pair[1] = safe_close(pair[1]);
-
-        r = wait_for_terminate(child, &si);
-        if (r < 0)
-                return r;
-        if (si.si_code != CLD_EXITED || si.si_status != EXIT_SUCCESS)
-                return -EIO;
-
-        if (recvmsg(pair[0], &mh, MSG_NOSIGNAL|MSG_CMSG_CLOEXEC) < 0)
-                return -errno;
-
-        for (cmsg = CMSG_FIRSTHDR(&mh); cmsg; cmsg = CMSG_NXTHDR(&mh, cmsg))
-                if (cmsg->cmsg_level == SOL_SOCKET && cmsg->cmsg_type == SCM_RIGHTS) {
-                        int *fds;
-                        unsigned n_fds;
-
-                        fds = (int*) CMSG_DATA(cmsg);
-                        n_fds = (cmsg->cmsg_len - CMSG_LEN(0)) / sizeof(int);
-
-                        if (n_fds != 1) {
-                                close_many(fds, n_fds);
-                                return -EIO;
-                        }
-
-                        master = fds[0];
-                }
-
+        master = openpt_in_namespace(m->leader, O_RDWR|O_NOCTTY|O_CLOEXEC);
         if (master < 0)
-                return -EIO;
+                return master;
 
         r = ptsname_malloc(master, &pty_name);
         if (r < 0)
@@ -495,6 +422,78 @@ int bus_machine_method_open_pty(sd_bus *bus, sd_bus_message *message, void *user
         return sd_bus_send(bus, reply, NULL);
 }
 
+int bus_machine_method_open_login(sd_bus *bus, sd_bus_message *message, void *userdata, sd_bus_error *error) {
+        _cleanup_bus_message_unref_ sd_bus_message *reply = NULL;
+        _cleanup_free_ char *pty_name = NULL, *getty = NULL;
+        _cleanup_bus_unref_ sd_bus *container_bus = NULL;
+        _cleanup_close_ int master = -1;
+        Machine *m = userdata;
+        const char *p;
+        int r;
+
+        master = openpt_in_namespace(m->leader, O_RDWR|O_NOCTTY|O_CLOEXEC);
+        if (master < 0)
+                return master;
+
+        r = ptsname_malloc(master, &pty_name);
+        if (r < 0)
+                return r;
+
+        p = path_startswith(pty_name, "/dev/pts/");
+        if (!p)
+                return sd_bus_error_setf(error, SD_BUS_ERROR_INVALID_ARGS, "PTS name %s is invalid", pty_name);
+
+        if (unlockpt(master) < 0)
+                return -errno;
+
+        r = sd_bus_new(&container_bus);
+        if (r < 0)
+                return r;
+
+#ifdef ENABLE_KDBUS
+        asprintf(&container_bus->address, "x-container-kernel:pid=" PID_FMT ";x-container-unix:pid=" PID_FMT, m->leader, m->leader);
+#else
+        asprintf(&container_bus->address, "x-container-kernel:pid=" PID_FMT, m->leader);
+#endif
+        if (!container_bus->address)
+                return -ENOMEM;
+
+        container_bus->bus_client = true;
+        container_bus->trusted = false;
+        container_bus->is_system = true;
+
+        r = sd_bus_start(container_bus);
+        if (r < 0)
+                return r;
+
+        getty = strjoin("container-getty@", p, ".service", NULL);
+        if (!getty)
+                return -ENOMEM;
+
+        r = sd_bus_call_method(
+                        container_bus,
+                        "org.freedesktop.systemd1",
+                        "/org/freedesktop/systemd1",
+                        "org.freedesktop.systemd1.Manager",
+                        "StartUnit",
+                        error, NULL,
+                        "ss", getty, "replace");
+        if (r < 0)
+                return r;
+
+        container_bus = sd_bus_unref(container_bus);
+
+        r = sd_bus_message_new_method_return(message, &reply);
+        if (r < 0)
+                return r;
+
+        r = sd_bus_message_append(reply, "hs", master, pty_name);
+        if (r < 0)
+                return r;
+
+        return sd_bus_send(bus, reply, NULL);
+}
+
 const sd_bus_vtable machine_vtable[] = {
         SD_BUS_VTABLE_START(0),
         SD_BUS_PROPERTY("Name", "s", NULL, offsetof(Machine, name), SD_BUS_VTABLE_PROPERTY_CONST),

src/machine/machine.h

@@ -105,6 +105,7 @@ int bus_machine_method_kill(sd_bus *bus, sd_bus_message *message, void *userdata
 int bus_machine_method_get_addresses(sd_bus *bus, sd_bus_message *message, void *userdata, sd_bus_error *error);
 int bus_machine_method_get_os_release(sd_bus *bus, sd_bus_message *message, void *userdata, sd_bus_error *error);
 int bus_machine_method_open_pty(sd_bus *bus, sd_bus_message *message, void *userdata, sd_bus_error *error);
+int bus_machine_method_open_login(sd_bus *bus, sd_bus_message *message, void *userdata, sd_bus_error *error);
 
 int machine_send_signal(Machine *m, bool new_machine);
 int machine_send_create_reply(Machine *m, sd_bus_error *error);

src/machine/machined-dbus.c

@@ -536,6 +536,27 @@ static int method_open_machine_pty(sd_bus *bus, sd_bus_message *message, void *u
         return bus_machine_method_open_pty(bus, message, machine, error);
 }
 
+static int method_open_machine_login(sd_bus *bus, sd_bus_message *message, void *userdata, sd_bus_error *error) {
+        Manager *m = userdata;
+        Machine *machine;
+        const char *name;
+        int r;
+
+        assert(bus);
+        assert(message);
+        assert(m);
+
+        r = sd_bus_message_read(message, "s", &name);
+        if (r < 0)
+                return sd_bus_error_set_errno(error, r);
+
+        machine = hashmap_get(m->machines, name);
+        if (!machine)
+                return sd_bus_error_setf(error, BUS_ERROR_NO_SUCH_MACHINE, "No machine '%s' known", name);
+
+        return bus_machine_method_open_login(bus, message, machine, error);
+}
+
 const sd_bus_vtable manager_vtable[] = {
         SD_BUS_VTABLE_START(0),
         SD_BUS_METHOD("GetMachine", "s", "o", method_get_machine, SD_BUS_VTABLE_UNPRIVILEGED),
@@ -552,6 +573,7 @@ const sd_bus_vtable manager_vtable[] = {
         SD_BUS_METHOD("GetMachineAddresses", "s", "a(iay)", method_get_machine_addresses, SD_BUS_VTABLE_UNPRIVILEGED),
         SD_BUS_METHOD("GetMachineOSRelease", "s", "a{ss}", method_get_machine_os_release, SD_BUS_VTABLE_UNPRIVILEGED),
         SD_BUS_METHOD("OpenMachinePTY", "s", "hs", method_open_machine_pty, 0),
+        SD_BUS_METHOD("OpenMachineLogin", "s", "hs", method_open_machine_login, 0),
         SD_BUS_SIGNAL("MachineNew", "so", 0),
         SD_BUS_SIGNAL("MachineRemoved", "so", 0),
         SD_BUS_VTABLE_END

src/shared/util.c

@@ -7473,3 +7473,89 @@ int ptsname_malloc(int fd, char **ret) {
                 l *= 2;
         }
 }
+
+int openpt_in_namespace(pid_t pid, int flags) {
+        _cleanup_close_ int pidnsfd = -1, mntnsfd = -1, rootfd = -1;
+        _cleanup_close_pair_ int pair[2] = { -1, -1 };
+        union {
+                struct cmsghdr cmsghdr;
+                uint8_t buf[CMSG_SPACE(sizeof(int))];
+        } control = {};
+        struct msghdr mh = {
+                .msg_control = &control,
+                .msg_controllen = sizeof(control),
+        };
+        struct cmsghdr *cmsg;
+        siginfo_t si;
+        pid_t child;
+        int r;
+
+        assert(pid > 0);
+
+        r = namespace_open(pid, &pidnsfd, &mntnsfd, NULL, &rootfd);
+        if (r < 0)
+                return r;
+
+        if (socketpair(AF_UNIX, SOCK_DGRAM, 0, pair) < 0)
+                return -errno;
+
+        child = fork();
+        if (child < 0)
+                return -errno;
+
+        if (child == 0) {
+                int master;
+
+                pair[0] = safe_close(pair[0]);
+
+                r = namespace_enter(pidnsfd, mntnsfd, -1, rootfd);
+                if (r < 0)
+                        _exit(EXIT_FAILURE);
+
+                master = posix_openpt(flags);
+                if (master < 0)
+                        _exit(EXIT_FAILURE);
+
+                cmsg = CMSG_FIRSTHDR(&mh);
+                cmsg->cmsg_level = SOL_SOCKET;
+                cmsg->cmsg_type = SCM_RIGHTS;
+                cmsg->cmsg_len = CMSG_LEN(sizeof(int));
+                memcpy(CMSG_DATA(cmsg), &master, sizeof(int));
+
+                mh.msg_controllen = cmsg->cmsg_len;
+
+                if (sendmsg(pair[1], &mh, MSG_NOSIGNAL) < 0)
+                        _exit(EXIT_FAILURE);
+
+                _exit(EXIT_SUCCESS);
+        }
+
+        pair[1] = safe_close(pair[1]);
+
+        r = wait_for_terminate(child, &si);
+        if (r < 0)
+                return r;
+        if (si.si_code != CLD_EXITED || si.si_status != EXIT_SUCCESS)
+                return -EIO;
+
+        if (recvmsg(pair[0], &mh, MSG_NOSIGNAL|MSG_CMSG_CLOEXEC) < 0)
+                return -errno;
+
+        for (cmsg = CMSG_FIRSTHDR(&mh); cmsg; cmsg = CMSG_NXTHDR(&mh, cmsg))
+                if (cmsg->cmsg_level == SOL_SOCKET && cmsg->cmsg_type == SCM_RIGHTS) {
+                        int *fds;
+                        unsigned n_fds;
+
+                        fds = (int*) CMSG_DATA(cmsg);
+                        n_fds = (cmsg->cmsg_len - CMSG_LEN(0)) / sizeof(int);
+
+                        if (n_fds != 1) {
+                                close_many(fds, n_fds);
+                                return -EIO;
+                        }
+
+                        return fds[0];
+                }
+
+        return -EIO;
+}

src/shared/util.h

@@ -1054,3 +1054,5 @@ int sethostname_idempotent(const char *s);
 #define laccess(path, mode) faccessat(AT_FDCWD, (path), (mode), AT_SYMLINK_NOFOLLOW)
 
 int ptsname_malloc(int fd, char **ret);
+
+int openpt_in_namespace(pid_t pid, int flags);