Fix the SIGSEGV that users have been reporting - don't execute anything

that had already been registered with atexit().

doc/index.html

@@ -184,7 +184,7 @@ regular <tt>rsa</tt> key for greatest compatibility.
 <h2>Change Log</h2>
 
 <ul>
-<li> <b>2019/08/11 Version 21:</b> Fix restarting after a crash.
+<li> <b>2019/08/11 Version 21:</b> Fix restarting after a crash.  Fix SIGSEGV on some Android 9 devices.
 <li> <b>2019/06/16 Version 20:</b> Update SDK.  Support x86_64, arm64.
 Fix finding support libraries.  Fix colors again.  Fix start-on-boot on
 new Android.  Update to dropbear 2019.78.

jni/interface.c

@@ -116,6 +116,16 @@ from_java_string(jobject s)
 	return ret;
 }
 
+
+/* this makes sure that no previously-added atexit gets called (some users have
+ * an atexit registered by libGLESv2_adreno.so */
+static void
+null_atexit(void)
+{
+	_Exit(0);
+}
+
+
 JNIEXPORT jint JNICALL
 Java_org_galexander_sshd_SimpleSSHDService_start_1sshd(JNIEnv *env_,
 	jclass cl,
@@ -146,6 +156,8 @@ Java_org_galexander_sshd_SimpleSSHDService_start_1sshd(JNIEnv *env_,
 		int retval;
 		int i;
 
+		atexit(null_atexit);
+
 		logfn = conf_path_file("dropbear.err");
 		logfn_old = conf_path_file("dropbear.err.old");
 		unlink(logfn_old);