8f8112f916
`systemd-resolved.service` runs as `User=systemd-resolved`, and uses certain Capabilit{y,ies} magic. By my understanding, this means it is started with a number of "privileges". Indeed, `capabilities(7)` explains > Linux divides the privileges traditionally > associated with superuser into distinct units, known as capabilities, > which can be independently enabled and disabled." This situation appears to contradict our current code comment which said > If we are not running as root we assume all privileges are already dropped. This appears to be a confusion in the comment only. The rest of the code tells a much clearer story. (Don't ask me if the story is correct. `capabilities(7)` scares me). Let's tweak the comment to make it consistent and avoid worrying readers about this.
111 lines
3.4 KiB
C
111 lines
3.4 KiB
C
/* SPDX-License-Identifier: LGPL-2.1+ */
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#include "sd-daemon.h"
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#include "sd-event.h"
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#include "capability-util.h"
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#include "mkdir.h"
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#include "resolved-conf.h"
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#include "resolved-manager.h"
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#include "resolved-resolv-conf.h"
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#include "selinux-util.h"
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#include "signal-util.h"
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#include "user-util.h"
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int main(int argc, char *argv[]) {
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_cleanup_(manager_freep) Manager *m = NULL;
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const char *user = "systemd-resolve";
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uid_t uid;
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gid_t gid;
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int r;
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log_set_target(LOG_TARGET_AUTO);
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log_parse_environment();
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log_open();
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if (argc != 1) {
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log_error("This program takes no arguments.");
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r = -EINVAL;
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goto finish;
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}
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umask(0022);
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r = mac_selinux_init();
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if (r < 0) {
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log_error_errno(r, "SELinux setup failed: %m");
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goto finish;
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}
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r = get_user_creds(&user, &uid, &gid, NULL, NULL, 0);
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if (r < 0) {
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log_error_errno(r, "Cannot resolve user name %s: %m", user);
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goto finish;
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}
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/* Always create the directory where resolv.conf will live */
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r = mkdir_safe_label("/run/systemd/resolve", 0755, uid, gid, MKDIR_WARN_MODE);
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if (r < 0) {
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log_error_errno(r, "Could not create runtime directory: %m");
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goto finish;
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}
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/* Drop privileges, but only if we have been started as root. If we are not running as root we assume most
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* privileges are already dropped. */
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if (getuid() == 0) {
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/* Drop privileges, but keep three caps. Note that we drop those too, later on (see below) */
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r = drop_privileges(uid, gid,
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(UINT64_C(1) << CAP_NET_RAW)| /* needed for SO_BINDTODEVICE */
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(UINT64_C(1) << CAP_NET_BIND_SERVICE)| /* needed to bind on port 53 */
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(UINT64_C(1) << CAP_SETPCAP) /* needed in order to drop the caps later */);
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if (r < 0)
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goto finish;
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}
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assert_se(sigprocmask_many(SIG_BLOCK, NULL, SIGTERM, SIGINT, SIGUSR1, SIGUSR2, SIGRTMIN+1, -1) >= 0);
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r = manager_new(&m);
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if (r < 0) {
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log_error_errno(r, "Could not create manager: %m");
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goto finish;
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}
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r = manager_start(m);
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if (r < 0) {
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log_error_errno(r, "Failed to start manager: %m");
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goto finish;
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}
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/* Write finish default resolv.conf to avoid a dangling symlink */
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(void) manager_write_resolv_conf(m);
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(void) manager_check_resolv_conf(m);
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/* Let's drop the remaining caps now */
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r = capability_bounding_set_drop(0, true);
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if (r < 0) {
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log_error_errno(r, "Failed to drop remaining caps: %m");
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goto finish;
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}
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sd_notify(false,
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"READY=1\n"
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"STATUS=Processing requests...");
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r = sd_event_loop(m->event);
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if (r < 0) {
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log_error_errno(r, "Event loop failed: %m");
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goto finish;
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}
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sd_event_get_exit_code(m->event, &r);
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finish:
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sd_notify(false,
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"STOPPING=1\n"
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"STATUS=Shutting down...");
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return r < 0 ? EXIT_FAILURE : EXIT_SUCCESS;
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}
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