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Fix FALLBACK_SCSV parsing
Fixed a bug in ssl_srv.c when parsing TLS_FALLBACK_SCSV in the ciphersuite list that caused it to miss it sometimes. Reported by Hugo Leisink as issue #810. Fix initially by @andreasag01; this commit isolates the bug fix and adds a non-regression test.
This commit is contained in:
Gilles Peskine
parent
b65c2be5f1
commit
d50177fdf3
@ -1,5 +1,11 @@
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mbed TLS ChangeLog (Sorted per branch, date)
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= mbed TLS 2.x.x branch released xxxx-xx-xx
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Security
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* Fixed offset in FALLBACK_SCSV parsing that caused TLS server to fail to
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detect it sometimes. Reported by Hugo Leisink. #810
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= mbed TLS 2.4.2 branch released 2017-03-08
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Security
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@ -1700,7 +1700,7 @@ read_record_header:
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#endif
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#if defined(MBEDTLS_SSL_FALLBACK_SCSV)
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for( i = 0, p = buf + 41 + sess_len; i < ciph_len; i += 2, p += 2 )
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for( i = 0, p = buf + ciph_offset + 2; i < ciph_len; i += 2, p += 2 )
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{
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if( p[0] == (unsigned char)( ( MBEDTLS_SSL_FALLBACK_SCSV_VALUE >> 8 ) & 0xff ) &&
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p[1] == (unsigned char)( ( MBEDTLS_SSL_FALLBACK_SCSV_VALUE ) & 0xff ) )
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86
tests/scripts/tcp_client.pl
Executable file
86
tests/scripts/tcp_client.pl
Executable file
@ -0,0 +1,86 @@
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#!/usr/bin/env perl
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# A simple TCP client that sends some data and expects a response.
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# Usage: tcp_client.pl HOSTNAME PORT DATA1 RESPONSE1
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# DATA: hex-encoded data to send to the server
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# RESPONSE: regexp that must match the server's response
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use warnings;
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use strict;
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use IO::Socket::INET;
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# Pack hex digits into a binary string, ignoring whitespace.
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sub parse_hex {
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my ($hex) = @_;
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$hex =~ s/\s+//g;
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return pack('H*', $hex);
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}
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## Open a TCP connection to the specified host and port.
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sub open_connection {
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my ($host, $port) = @_;
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my $socket = IO::Socket::INET->new(PeerAddr => $host,
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PeerPort => $port,
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Proto => 'tcp',
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Timeout => 1);
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die "Cannot connect to $host:$port: $!" unless $socket;
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return $socket;
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}
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## Close the TCP connection.
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sub close_connection {
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my ($connection) = @_;
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$connection->shutdown(2);
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# Ignore shutdown failures (at least for now)
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return 1;
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}
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## Write the given data, expressed as hexadecimal
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sub write_data {
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my ($connection, $hexdata) = @_;
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my $data = parse_hex($hexdata);
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my $total_sent = 0;
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while ($total_sent < length($data)) {
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my $sent = $connection->send($data, 0);
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if (!defined $sent) {
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die "Unable to send data: $!";
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}
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$total_sent += $sent;
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}
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return 1;
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}
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## Read a response and check it against an expected prefix
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sub read_response {
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my ($connection, $expected_hex) = @_;
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my $expected_data = parse_hex($expected_hex);
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my $start_offset = 0;
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while ($start_offset < length($expected_data)) {
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my $actual_data;
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my $ok = $connection->recv($actual_data, length($expected_data));
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if (!defined $ok) {
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die "Unable to receive data: $!";
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}
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if (($actual_data ^ substr($expected_data, $start_offset)) =~ /[^\000]/) {
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printf STDERR ("Received \\x%02x instead of \\x%02x at offset %d\n",
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ord(substr($actual_data, $-[0], 1)),
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ord(substr($expected_data, $start_offset + $-[0], 1)),
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$start_offset + $-[0]);
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return 0;
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}
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$start_offset += length($actual_data);
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}
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return 1;
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}
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if (@ARGV != 4) {
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print STDERR "Usage: $0 HOSTNAME PORT DATA1 RESPONSE1\n";
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exit(3);
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}
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my ($host, $port, $data1, $response1) = @ARGV;
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my $connection = open_connection($host, $port);
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write_data($connection, $data1);
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if (!read_response($connection, $response1)) {
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exit(1);
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}
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close_connection($connection);
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@ -28,11 +28,13 @@ set -u
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: ${OPENSSL_CMD:=openssl} # OPENSSL would conflict with the build system
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: ${GNUTLS_CLI:=gnutls-cli}
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: ${GNUTLS_SERV:=gnutls-serv}
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: ${PERL:=perl}
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O_SRV="$OPENSSL_CMD s_server -www -cert data_files/server5.crt -key data_files/server5.key"
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O_CLI="echo 'GET / HTTP/1.0' | $OPENSSL_CMD s_client"
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G_SRV="$GNUTLS_SERV --x509certfile data_files/server5.crt --x509keyfile data_files/server5.key"
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G_CLI="echo 'GET / HTTP/1.0' | $GNUTLS_CLI --x509cafile data_files/test-ca_cat12.crt"
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TCP_CLIENT="$PERL scripts/tcp_client.pl"
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TESTS=0
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FAILS=0
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@ -965,6 +967,37 @@ run_test "Fallback SCSV: enabled, max version, openssl client" \
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-s "received FALLBACK_SCSV" \
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-S "inapropriate fallback"
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## ClientHello generated with
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## "openssl s_client -CAfile tests/data_files/test-ca.crt -tls1_1 -connect localhost:4433 -cipher ..."
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## then manually twiddling the ciphersuite list.
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## The ClientHello content is spelled out below as a hex string as
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## "prefix ciphersuite1 ciphersuite2 ciphersuite3 ciphersuite4 suffix".
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## The expected response is an inappropriate_fallback alert.
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requires_openssl_with_fallback_scsv
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run_test "Fallback SCSV: beginning of list" \
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"$P_SRV debug_level=2" \
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"$TCP_CLIENT localhost $SRV_PORT '160301003e0100003a03022aafb94308dc22ca1086c65acc00e414384d76b61ecab37df1633b1ae1034dbe000008 5600 0031 0032 0033 0100000900230000000f000101' '15030200020256'" \
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0 \
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-s "received FALLBACK_SCSV" \
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-s "inapropriate fallback"
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requires_openssl_with_fallback_scsv
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run_test "Fallback SCSV: end of list" \
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"$P_SRV debug_level=2" \
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"$TCP_CLIENT localhost $SRV_PORT '160301003e0100003a03022aafb94308dc22ca1086c65acc00e414384d76b61ecab37df1633b1ae1034dbe000008 0031 0032 0033 5600 0100000900230000000f000101' '15030200020256'" \
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0 \
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-s "received FALLBACK_SCSV" \
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-s "inapropriate fallback"
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## Here the expected response is a valid ServerHello prefix, up to the random.
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requires_openssl_with_fallback_scsv
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run_test "Fallback SCSV: not in list" \
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"$P_SRV debug_level=2" \
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"$TCP_CLIENT localhost $SRV_PORT '160301003e0100003a03022aafb94308dc22ca1086c65acc00e414384d76b61ecab37df1633b1ae1034dbe000008 0056 0031 0032 0033 0100000900230000000f000101' '16030200300200002c0302'" \
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0 \
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-S "received FALLBACK_SCSV" \
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-S "inapropriate fallback"
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# Tests for CBC 1/n-1 record splitting
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run_test "CBC Record splitting: TLS 1.2, no splitting" \
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