/* sets the DTLS MTU and returns the actual tunnel MTU */
unsigned dtls_set_mtu(struct openconnect_info *vpninfo, unsigned mtu)
{
/* This is the record MTU (not the link MTU, which includes
* IP+UDP headers, and not the payload MTU */
SSL_set_mtu(vpninfo->dtls_ssl, mtu);
#ifdef DTLS_get_data_mtu
return DTLS_get_data_mtu(vpninfo->dtls_ssl);
#else
return dtls_get_data_mtu(vpninfo, mtu);
#endif
}
static int mtu_test(SSL_CTX *ctx, const char *cs, int no_etm)
{
SSL *srvr_ssl = NULL, *clnt_ssl = NULL;
BIO *sc_bio = NULL;
int i;
size_t s;
size_t mtus[30];
unsigned char buf[600];
int rv = 0;
memset(buf, 0x5a, sizeof(buf));
if (create_ssl_objects(ctx, ctx, &srvr_ssl, &clnt_ssl, NULL, NULL) != 1)
goto out;
if (no_etm)
SSL_set_options(srvr_ssl, SSL_OP_NO_ENCRYPT_THEN_MAC);
if (SSL_set_cipher_list(srvr_ssl, cs) != 1 ||
SSL_set_cipher_list(clnt_ssl, cs) != 1) {
ERR_print_errors_fp(stdout);
goto out;
}
sc_bio = SSL_get_rbio(srvr_ssl);
if (create_ssl_connection(clnt_ssl, srvr_ssl) != 1)
goto out;
if (debug)
printf("Channel established\n");
/* For record MTU values between 500 and 539, call DTLS_get_data_mtu()
* to query the payload MTU which will fit. */
for (i = 0; i < 30; i++) {
SSL_set_mtu(clnt_ssl, 500 + i);
mtus[i] = DTLS_get_data_mtu(clnt_ssl);
if (debug)
printf("%s%s payload MTU for record mtu %d = %"OSSLzu"\n",
cs, no_etm ? "-noEtM":"", 500 + i, mtus[i]);
if (mtus[i] == 0) {
fprintf(stderr,
"payload MTU failed with record MTU %d for %s\n",
500 + i, cs);
goto out;
}
}
/* Now get out of the way */
SSL_set_mtu(clnt_ssl, 1000);
/* Now for all values in the range of payload MTUs, send
* a payload of that size and see what actual record size
* we end up with. */
for (s = mtus[0]; s <= mtus[29]; s++) {
size_t reclen;
if (SSL_write(clnt_ssl, buf, s) != (int)s) {
ERR_print_errors_fp(stdout);
goto out;
}
reclen = BIO_read(sc_bio, buf, sizeof(buf));
if (debug)
printf("record %"OSSLzu" for payload %"OSSLzu"\n", reclen, s);
for (i = 0; i < 30; i++) {
/* DTLS_get_data_mtu() with record MTU 500+i returned mtus[i] ... */
if (s <= mtus[i] && reclen > (size_t)(500 + i)) {
/* We sent a packet smaller than or equal to mtus[j] and
* that made a record *larger* than the record MTU 500+j! */
fprintf(stderr,
"%s: Payload MTU %"OSSLzu" reported for record MTU %d\n"
"but sending a payload of %"OSSLzu" made a record of %"OSSLzu"(too large)\n",
cs, mtus[i], 500 + i, s, reclen);
goto out;
}
if (s > mtus[i] && reclen <= (size_t)(500 + i)) {
/* We sent a *larger* packet than mtus[i] and that *still*
* fits within the record MTU 500+i, so DTLS_get_data_mtu()
* was overly pessimistic. */
fprintf(stderr,
"%s: Payload MTU %"OSSLzu" reported for record MTU %d\n"
"but sending a payload of %"OSSLzu" made a record of %"OSSLzu" (too small)\n",
cs, mtus[i], 500 + i, s, reclen);
goto out;
}
}
}
rv = 1;
if (SSL_USE_ETM(clnt_ssl))
rv = 2;
out:
SSL_free(clnt_ssl);
SSL_free(srvr_ssl);
return rv;
}
