Mysterious segfaults

gistfile1.txt

#
# A fatal error has been detected by the Java Runtime Environment:
#
#  SIGSEGV (0xb) at pc=0x00007f374472b284, pid=5745, tid=139875359385344
#
# JRE version: Java(TM) SE Runtime Environment (7.0_40-b43) (build 1.7.0_40-b43)
# Java VM: Java HotSpot(TM) 64-Bit Server VM (24.0-b56 mixed mode linux-amd64 compressed oops)
# Problematic frame:
# C  [libc.so.6+0x138284]  __nss_passwd_lookup+0x166a4

JTox.c

JNIEXPORT jint JNICALL Java_im_tox_jtoxcore_JTox_tox_1addfriend(JNIEnv * env,
		jobject obj, jlong messenger, jstring address, jstring data) {
	const uint8_t *_address = (*env)->GetStringUTFChars(env, address, 0);
	const uint8_t *_data = (*env)->GetStringUTFChars(env, data, 0);

	uint8_t __address[TOX_FRIEND_ADDRESS_SIZE];
	hex_to_addr(_address, __address);
	printf("beep\n");
	fflush(stdout);
        
	uint8_t *__data = malloc(strlen(_data) + 1); //Sometimes it segfaults here
	printf("beep\n");
	fflush(stdout);

	memcpy(__data, _data, strlen(_data) + 1); // If it didn't segfault above, it segfaults here
	printf("beep\n");
	fflush(stdout);

	(*env)->ReleaseStringUTFChars(env, address, _address);
	(*env)->ReleaseStringUTFChars(env, data, _data);

	int ret = tox_addfriend(((tox_jni_globals_t *) messenger)->tox, __address,
			__data, strlen(__data) + 1);
	free(__data);
	return ret;
}