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-rw-r--r--src/daemon.c250
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diff --git a/src/daemon.c b/src/daemon.c
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+++ b/src/daemon.c
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+/*
+ * Copyright (c) 2016-2021, OARC, Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in
+ * the documentation and/or other materials provided with the
+ * distribution.
+ *
+ * 3. Neither the name of the copyright holder nor the names of its
+ * contributors may be used to endorse or promote products derived
+ * from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "config.h"
+
+#include "daemon.h"
+#include "log.h"
+#include "memzero.h"
+
+void drop_privileges(void)
+{
+ struct rlimit rss;
+ struct passwd pwd;
+ struct passwd* result = 0;
+ size_t pwdBufSize;
+ char* pwdBuf;
+ unsigned int s;
+ uid_t oldUID = getuid();
+ uid_t oldGID = getgid();
+ uid_t dropUID;
+ gid_t dropGID;
+ const char* user;
+ struct group* grp = 0;
+
+ /*
+ * Security: getting UID and GUID for nobody
+ */
+ pwdBufSize = sysconf(_SC_GETPW_R_SIZE_MAX);
+ if (pwdBufSize == -1)
+ pwdBufSize = 16384;
+
+ pwdBuf = calloc(pwdBufSize, sizeof(char));
+ if (pwdBuf == NULL) {
+ fprintf(stderr, "unable to allocate buffer for pwdBuf\n");
+ exit(1);
+ }
+
+ user = options.user ? options.user : DROPTOUSER;
+ if (options.group) {
+ if (!(grp = getgrnam(options.group))) {
+ if (errno) {
+ fprintf(stderr, "Unable to get group %s: %s\n", options.group, strerror(errno));
+ } else {
+ fprintf(stderr, "Group %s not found, existing.\n", options.group);
+ }
+ exit(1);
+ }
+ }
+
+ s = getpwnam_r(user, &pwd, pwdBuf, pwdBufSize, &result);
+ if (result == NULL) {
+ if (s == 0) {
+ fprintf(stderr, "User %s not found, exiting.\n", user);
+ exit(1);
+ } else {
+ fprintf(stderr, "issue with getpwnnam_r call, exiting.\n");
+ exit(1);
+ }
+ }
+
+ dropUID = pwd.pw_uid;
+ dropGID = grp ? grp->gr_gid : pwd.pw_gid;
+ dnscap_memzero(pwdBuf, pwdBufSize);
+ free(pwdBuf);
+
+ /*
+ * Security section: setting memory limit and dropping privileges to nobody
+ */
+ getrlimit(RLIMIT_DATA, &rss);
+ if (mem_limit_set) {
+ rss.rlim_cur = mem_limit;
+ rss.rlim_max = mem_limit;
+ if (setrlimit(RLIMIT_DATA, &rss) == -1) {
+ fprintf(stderr, "Unable to set the memory limit, exiting\n");
+ exit(1);
+ }
+ }
+
+#if HAVE_SETRESGID
+ if (setresgid(dropGID, dropGID, dropGID) < 0) {
+ fprintf(stderr, "Unable to drop GID to %s: %s\n", options.group ? options.group : user, strerror(errno));
+ exit(1);
+ }
+#elif HAVE_SETREGID
+ if (setregid(dropGID, dropGID) < 0) {
+ fprintf(stderr, "Unable to drop GID to %s: %s\n", options.group ? options.group : user, strerror(errno));
+ exit(1);
+ }
+#elif HAVE_SETEGID
+ if (setegid(dropGID) < 0) {
+ fprintf(stderr, "Unable to drop GID to %s: %s\n", options.group ? options.group : user, strerror(errno));
+ exit(1);
+ }
+#endif
+
+#if HAVE_INITGROUPS
+ if (initgroups(pwd.pw_name, dropGID) < 0) {
+ fprintf(stderr, "Unable to init supplemental groups for %s: %s\n", user, strerror(errno));
+ exit(1);
+ }
+#elif HAVE_SETGROUPS
+ if (setgroups(0, NULL) < 0) {
+ fprintf(stderr, "Unable to drop supplemental groups: %s\n", strerror(errno));
+ exit(1);
+ }
+#endif
+
+#if HAVE_SETRESUID
+ if (setresuid(dropUID, dropUID, dropUID) < 0) {
+ fprintf(stderr, "Unable to drop UID to %s: %s\n", user, strerror(errno));
+ exit(1);
+ }
+#elif HAVE_SETREUID
+ if (setreuid(dropUID, dropUID) < 0) {
+ fprintf(stderr, "Unable to drop UID to %s: %s\n", user, strerror(errno));
+ exit(1);
+ }
+#elif HAVE_SETEUID
+ if (seteuid(dropUID) < 0) {
+ fprintf(stderr, "Unable to drop UID to %s: %s\n", user, strerror(errno));
+ exit(1);
+ }
+#endif
+
+ /*
+ * Testing if privileges are dropped
+ */
+ if (oldGID != getgid() && (setgid(oldGID) == 1 && setegid(oldGID) != 1)) {
+ fprintf(stderr, "Able to restore back to root, exiting.\n");
+ fprintf(stderr, "currentUID:%u currentGID:%u\n", getuid(), getgid());
+ exit(1);
+ }
+ if ((oldUID != getuid() && getuid() == 0) && (setuid(oldUID) != 1 && seteuid(oldUID) != 1)) {
+ fprintf(stderr, "Able to restore back to root, exiting.\n");
+ fprintf(stderr, "currentUID:%u currentGID:%u\n", getgid(), getgid());
+ exit(1);
+ }
+
+#ifdef USE_SECCOMP
+ if (use_seccomp == FALSE) {
+ return;
+ }
+
+#if 0
+ /*
+ * Setting SCMP_ACT_TRAP means the process will get
+ * a SIGSYS signal when a bad syscall is executed
+ * This is for debugging and should be monitored.
+ */
+
+ scmp_filter_ctx ctx = seccomp_init(SCMP_ACT_TRAP);
+#endif
+
+ /*
+ * SCMP_ACT_KILL tells the kernel to kill the process
+ * when a syscall we did not filter on is called.
+ * This should be uncommented in production.
+ */
+ scmp_filter_ctx ctx = seccomp_init(SCMP_ACT_KILL);
+
+ if (ctx == NULL) {
+ fprintf(stderr, "Unable to create seccomp-bpf context\n");
+ exit(1);
+ }
+
+ int r = 0;
+ r |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(setsockopt), 0);
+ r |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(uname), 0);
+ r |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(mmap), 0);
+ r |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(munmap), 0);
+ r |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(read), 0);
+ r |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(open), 0);
+ r |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(write), 0);
+ r |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(close), 0);
+ r |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(fstat), 0);
+ r |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(lseek), 0);
+ r |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(select), 0);
+ r |= seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(stat), 0);
+
+ if (r != 0) {
+ fprintf(stderr, "Unable to apply seccomp-bpf filter\n");
+ seccomp_release(ctx);
+ exit(1);
+ }
+
+ r = seccomp_load(ctx);
+
+ if (r < 0) {
+ seccomp_release(ctx);
+ fprintf(stderr, "Unable to load seccomp-bpf filter\n");
+ exit(1);
+ }
+#endif
+}
+
+void daemonize(void)
+{
+ pid_t pid;
+#ifdef TIOCNOTTY
+ int i;
+#endif
+ if ((pid = fork()) < 0) {
+ logerr("fork failed: %s", strerror(errno));
+ exit(1);
+ } else if (pid > 0)
+ exit(0);
+ openlog("dnscap", 0, LOG_DAEMON);
+ if (setsid() < 0) {
+ logerr("setsid failed: %s", strerror(errno));
+ exit(1);
+ }
+#ifdef TIOCNOTTY
+ if ((i = open("/dev/tty", O_RDWR)) >= 0) {
+ ioctl(i, TIOCNOTTY, NULL);
+ close(i);
+ }
+#endif
+ logerr("Backgrounded as pid %u", getpid());
+}
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