systemctl: support remote and privileged systemctl access via SSH and pkexec

This adds support for executing systemctl operations remotely or as
privileged user while still running systemctl itself unprivileged and
locally.

This currently requires a D-Bus patch to work properly.

https://bugs.freedesktop.org/show_bug.cgi?id=35230

1 files changed, 367 insertions, 0 deletions

diff --git a/src/bridge.c b/src/bridge.c
new file mode 100644
index 0000000000..5ee058a37f
--- /dev/null
+++ b/src/bridge.c
@@ -0,0 +1,367 @@
+/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
+
+/***
+  This file is part of systemd.
+
+  Copyright 2010 Lennart Poettering
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU General Public License as published by
+  the Free Software Foundation; either version 2 of the License, or
+  (at your option) any later version.
+
+  systemd is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+#include <sys/socket.h>
+#include <sys/un.h>
+#include <sys/types.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <string.h>
+#include <errno.h>
+#include <sys/epoll.h>
+#include <stddef.h>
+
+#include "log.h"
+#include "util.h"
+#include "socket-util.h"
+
+#define BUFFER_SIZE (64*1024)
+#define EXTRA_SIZE 16
+
+static bool initial_nul = false;
+static bool auth_over = false;
+
+static void format_uid(char *buf, size_t l) {
+        char text[20 + 1]; /* enough space for a 64bit integer plus NUL */
+        unsigned j;
+
+        assert(l > 0);
+
+        snprintf(text, sizeof(text)-1, "%llu", (unsigned long long) geteuid());
+        text[sizeof(text)-1] = 0;
+
+        memset(buf, 0, l);
+
+        for (j = 0; text[j] && j*2+2 < l; j++) {
+                buf[j*2]   = hexchar(text[j] >> 4);
+                buf[j*2+1] = hexchar(text[j] & 0xF);
+        }
+
+        buf[j*2] = 0;
+}
+
+static size_t patch_in_line(char *line, size_t l, size_t left) {
+        size_t r;
+
+        if (line[0] == 0 && !initial_nul) {
+                initial_nul = true;
+                line += 1;
+                l -= 1;
+                r = 1;
+        } else
+                r = 0;
+
+        if (l == 5 && strncmp(line, "BEGIN", 5) == 0) {
+                r += l;
+                auth_over = true;
+
+        } else if (l == 17 && strncmp(line, "NEGOTIATE_UNIX_FD", 17) == 0) {
+                memmove(line + 13, line + 17, left);
+                memcpy(line, "NEGOTIATE_NOP", 13);
+                r += 13;
+
+        } else if (l >= 14 && strncmp(line, "AUTH EXTERNAL ", 14) == 0) {
+                char uid[20*2 + 1];
+                size_t len;
+
+                format_uid(uid, sizeof(uid));
+                len = strlen(uid);
+                assert(len <= EXTRA_SIZE);
+
+                memmove(line + 14 + len, line + l, left);
+                memcpy(line + 14, uid, len);
+
+                r += 14 + len;
+        } else
+                r += l;
+
+        return r;
+}
+
+static size_t patch_in_buffer(char* in_buffer, size_t *in_buffer_full) {
+        size_t i, good = 0;
+
+        if (*in_buffer_full <= 0)
+                return *in_buffer_full;
+
+        /* If authentication is done, we don't touch anything anymore */
+        if (auth_over)
+                return *in_buffer_full;
+
+        if (*in_buffer_full < 2)
+                return 0;
+
+        for (i = 0; i <= *in_buffer_full - 2; i ++) {
+
+                /* Fully lines can be send on */
+                if (in_buffer[i] == '\r' && in_buffer[i+1] == '\n') {
+                        if (i > good) {
+                                size_t old_length, new_length;
+
+                                old_length = i - good;
+                                new_length = patch_in_line(in_buffer+good, old_length, *in_buffer_full - i);
+                                *in_buffer_full = *in_buffer_full + new_length - old_length;
+
+                                good += new_length + 2;
+
+                        } else
+                                good = i+2;
+                }
+
+                if (auth_over)
+                        break;
+        }
+
+        return good;
+}
+
+int main(int argc, char *argv[]) {
+        int r = EXIT_FAILURE, fd = -1, ep = -1;
+        union sockaddr_union sa;
+        char in_buffer[BUFFER_SIZE+EXTRA_SIZE], out_buffer[BUFFER_SIZE+EXTRA_SIZE];
+        size_t in_buffer_full = 0, out_buffer_full = 0;
+        struct epoll_event stdin_ev, stdout_ev, fd_ev;
+        bool stdin_readable = false, stdout_writable = false, fd_readable = false, fd_writable = false;
+        bool stdin_rhup = false, stdout_whup = false, fd_rhup = false, fd_whup = false;
+
+        if (argc > 1) {
+                log_error("This program takes no argument.");
+                return EXIT_FAILURE;
+        }
+
+        log_set_target(LOG_TARGET_SYSLOG_OR_KMSG);
+        log_parse_environment();
+        log_open();
+
+        if ((fd = socket(AF_UNIX, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0)) < 0) {
+                log_error("Failed to create socket: %s", strerror(errno));
+                goto finish;
+        }
+
+        zero(sa);
+        sa.un.sun_family = AF_UNIX;
+        strncpy(sa.un.sun_path, "/var/run/dbus/system_bus_socket", sizeof(sa.un.sun_path));
+
+        if (connect(fd, &sa.sa, offsetof(struct sockaddr_un, sun_path) + 1 + strlen(sa.un.sun_path+1)) < 0) {
+                log_error("Failed to connect: %m");
+                goto finish;
+        }
+
+        fd_nonblock(STDIN_FILENO, 1);
+        fd_nonblock(STDOUT_FILENO, 1);
+
+        if ((ep = epoll_create1(EPOLL_CLOEXEC)) < 0) {
+                log_error("Failed to create epoll: %m");
+                goto finish;
+        }
+
+        zero(stdin_ev);
+        stdin_ev.events = EPOLLIN|EPOLLET;
+        stdin_ev.data.fd = STDIN_FILENO;
+
+        zero(stdout_ev);
+        stdout_ev.events = EPOLLOUT|EPOLLET;
+        stdout_ev.data.fd = STDOUT_FILENO;
+
+        zero(fd_ev);
+        fd_ev.events = EPOLLIN|EPOLLOUT|EPOLLET;
+        fd_ev.data.fd = fd;
+
+        if (epoll_ctl(ep, EPOLL_CTL_ADD, STDIN_FILENO, &stdin_ev) < 0 ||
+            epoll_ctl(ep, EPOLL_CTL_ADD, STDOUT_FILENO, &stdout_ev) < 0 ||
+            epoll_ctl(ep, EPOLL_CTL_ADD, fd, &fd_ev) < 0) {
+                log_error("Failed to regiser fds in epoll: %m");
+                goto finish;
+        }
+
+        do {
+                struct epoll_event ev[16];
+                ssize_t k;
+                int i, nfds;
+
+                if ((nfds = epoll_wait(ep, ev, ELEMENTSOF(ev), -1)) < 0) {
+
+                        if (errno == EINTR || errno == EAGAIN)
+                                continue;
+
+                        log_error("epoll_wait(): %m");
+                        goto finish;
+                }
+
+                assert(nfds >= 1);
+
+                for (i = 0; i < nfds; i++) {
+                        if (ev[i].data.fd == STDIN_FILENO) {
+
+                                if (!stdin_rhup && (ev[i].events & (EPOLLHUP|EPOLLIN)))
+                                        stdin_readable = true;
+
+                        } else if (ev[i].data.fd == STDOUT_FILENO) {
+
+                                if (ev[i].events & EPOLLHUP) {
+                                        stdout_writable = false;
+                                        stdout_whup = true;
+                                }
+
+                                if (!stdout_whup && (ev[i].events & EPOLLOUT))
+                                        stdout_writable = true;
+
+                        } else if (ev[i].data.fd == fd) {
+
+                                if (ev[i].events & EPOLLHUP) {
+                                        fd_writable = false;
+                                        fd_whup = true;
+                                }
+
+                                if (!fd_rhup && (ev[i].events & (EPOLLHUP|EPOLLIN)))
+                                        fd_readable = true;
+
+                                if (!fd_whup && (ev[i].events & EPOLLOUT))
+                                        fd_writable = true;
+                        }
+                }
+
+                while ((stdin_readable && in_buffer_full <= 0) ||
+                       (fd_writable && patch_in_buffer(in_buffer, &in_buffer_full) > 0) ||
+                       (fd_readable && out_buffer_full <= 0) ||
+                       (stdout_writable && out_buffer_full > 0)) {
+
+                        size_t in_buffer_good = 0;
+
+                        if (stdin_readable && in_buffer_full < BUFFER_SIZE) {
+
+                                if ((k = read(STDIN_FILENO, in_buffer + in_buffer_full, BUFFER_SIZE - in_buffer_full)) < 0) {
+
+                                        if (errno == EAGAIN)
+                                                stdin_readable = false;
+                                        else if (errno == EPIPE || errno == ECONNRESET)
+                                                k = 0;
+                                        else {
+                                                log_error("read(): %m");
+                                                goto finish;
+                                        }
+                                } else
+                                        in_buffer_full += (size_t) k;
+
+                                if (k == 0) {
+                                        stdin_rhup = true;
+                                        stdin_readable = false;
+                                        shutdown(STDIN_FILENO, SHUT_RD);
+                                        close_nointr_nofail(STDIN_FILENO);
+                                }
+                        }
+
+                        in_buffer_good = patch_in_buffer(in_buffer, &in_buffer_full);
+
+                        if (fd_writable && in_buffer_good > 0) {
+
+                                if ((k = write(fd, in_buffer, in_buffer_good)) < 0) {
+
+                                        if (errno == EAGAIN)
+                                                fd_writable = false;
+                                        else if (errno == EPIPE || errno == ECONNRESET) {
+                                                fd_whup = true;
+                                                fd_writable = false;
+                                                shutdown(fd, SHUT_WR);
+                                        } else {
+                                                log_error("write(): %m");
+                                                goto finish;
+                                        }
+
+                                } else {
+                                        assert(in_buffer_full >= (size_t) k);
+                                        memmove(in_buffer, in_buffer + k, in_buffer_full - k);
+                                        in_buffer_full -= k;
+                                }
+                        }
+
+                        if (fd_readable && out_buffer_full < BUFFER_SIZE) {
+
+                                if ((k = read(fd, out_buffer + out_buffer_full, BUFFER_SIZE - out_buffer_full)) < 0) {
+
+                                        if (errno == EAGAIN)
+                                                fd_readable = false;
+                                        else if (errno == EPIPE || errno == ECONNRESET)
+                                                k = 0;
+                                        else {
+                                                log_error("read(): %m");
+                                                goto finish;
+                                        }
+                                }  else
+                                        out_buffer_full += (size_t) k;
+
+                                if (k == 0) {
+                                        fd_rhup = true;
+                                        fd_readable = false;
+                                        shutdown(fd, SHUT_RD);
+                                }
+                        }
+
+                        if (stdout_writable && out_buffer_full > 0) {
+
+                                if ((k = write(STDOUT_FILENO, out_buffer, out_buffer_full)) < 0) {
+
+                                        if (errno == EAGAIN)
+                                                stdout_writable = false;
+                                        else if (errno == EPIPE || errno == ECONNRESET) {
+                                                stdout_whup = true;
+                                                stdout_writable = false;
+                                                shutdown(STDOUT_FILENO, SHUT_WR);
+                                                close_nointr(STDOUT_FILENO);
+                                        } else {
+                                                log_error("write(): %m");
+                                                goto finish;
+                                        }
+
+                                } else {
+                                        assert(out_buffer_full >= (size_t) k);
+                                        memmove(out_buffer, out_buffer + k, out_buffer_full - k);
+                                        out_buffer_full -= k;
+                                }
+                        }
+                }
+
+                if (stdin_rhup && in_buffer_full <= 0 && !fd_whup) {
+                        fd_whup = true;
+                        fd_writable = false;
+                        shutdown(fd, SHUT_WR);
+                }
+
+                if (fd_rhup && out_buffer_full <= 0 && !stdout_whup) {
+                        stdout_whup = true;
+                        stdout_writable = false;
+                        shutdown(STDOUT_FILENO, SHUT_WR);
+                        close_nointr(STDOUT_FILENO);
+                }
+
+        } while (!stdout_whup || !fd_whup);
+
+        r = EXIT_SUCCESS;
+
+finish:
+        if (fd >= 0)
+                close_nointr_nofail(fd);
+
+        if (ep >= 0)
+                close_nointr_nofail(ep);
+
+        return r;
+}