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Implement FALLBACK_SCSV client-side

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This commit is contained in:
Manuel Pégourié-Gonnard 2014-10-20 13:34:59 +02:00
parent a6c5ea2c43
commit 1cbd39dbeb
6 changed files with 144 additions and 1 deletions
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17
include/polarssl/config.h
View File

@ -811,6 +811,23 @@
*/
//#define POLARSSL_SSL_DEBUG_ALL
/**
* \def POLARSSL_SSL_FALLBACK_SCSV
*
* Enable support for FALLBACK_SCSV (draft-ietf-tls-downgrade-scsv-00).
*
* For servers, it is recommended to always enable this, unless you support
* only one version of TLS, or know for sure that none of your clients
* implements a fallback strategy.
*
* For clients, you only need this if you're using a fallback strategy, which
* is not recommended in the first place, unless you absolutely need it to
* interoperate with buggy (version-intolerant) servers.
*
* Comment this macro to disable support for FALLBACK_SCSV
*/
#define POLARSSL_SSL_FALLBACK_SCSV
/**
* \def POLARSSL_SSL_HW_RECORD_ACCEL
*

32
include/polarssl/ssl.h
View File

@ -206,6 +206,9 @@
#define SSL_IS_CLIENT 0
#define SSL_IS_SERVER 1
#define SSL_IS_NOT_FALLBACK 0
#define SSL_IS_FALLBACK 1
#define SSL_COMPRESS_NULL 0
#define SSL_COMPRESS_DEFLATE 1
@ -308,6 +311,7 @@
* Signaling ciphersuite values (SCSV)
*/
#define SSL_EMPTY_RENEGOTIATION_INFO 0xFF /**< renegotiation info ext */
#define SSL_FALLBACK_SCSV 0x5600 /**< draft-ietf-tls-downgrade-scsv-00 */
/*
* Supported Signature and Hash algorithms (For TLS 1.2)
@ -697,6 +701,10 @@ struct _ssl_context
int min_major_ver; /*!< min. major version used */
int min_minor_ver; /*!< min. minor version used */
#if defined(POLARSSL_SSL_FALLBACK_SCSV) && defined(POLARSSL_SSL_CLI_C)
char fallback; /*!< flag for fallback connections */
#endif
/*
* Callbacks (RNG, debug, I/O, verification)
*/
@ -1367,7 +1375,6 @@ const char *ssl_get_alpn_protocol( const ssl_context *ssl );
*/
void ssl_set_max_version( ssl_context *ssl, int major, int minor );
/**
* \brief Set the minimum accepted SSL/TLS protocol version
* (Default: SSL_MIN_MAJOR_VERSION, SSL_MIN_MINOR_VERSION)
@ -1383,6 +1390,29 @@ void ssl_set_max_version( ssl_context *ssl, int major, int minor );
*/
void ssl_set_min_version( ssl_context *ssl, int major, int minor );
#if defined(POLARSSL_SSL_FALLBACK_SCSV) && defined(POLARSSL_SSL_CLI_C)
/**
* \brief Set the fallback flag (client-side only).
* (Default: SSL_IS_NOT_FALLBACK).
*
* \note Set to SSL_IS_FALLBACK when preparing a fallback
* connection, that is a connection with max_version set to a
* lower value than the value you're willing to use. Such
* fallback connections are not recommended but are sometimes
* necessary to interoperate with buggy (version-intolerant)
* servers.
*
* \warning You should NOT set this to SSL_IS_FALLBACK for
* non-fallback connections! This would appear to work for a
* while, then cause failures when the server is upgraded to
* support a newer TLS version.
*
* \param ssl SSL context
* \param fallback SSL_IS_NOT_FALLBACK or SSL_IS_FALLBACK
*/
void ssl_set_fallback( ssl_context *ssl, char fallback );
#endif /* POLARSSL_SSL_FALLBACK_SCSV && POLARSSL_SSL_CLI_C */
#if defined(POLARSSL_SSL_MAX_FRAGMENT_LENGTH)
/**
* \brief Set the maximum fragment length to emit and/or negotiate

11
library/ssl_cli.c
View File

@ -596,6 +596,17 @@ static int ssl_write_client_hello( ssl_context *ssl )
*p++ = (unsigned char)( ciphersuites[i] );
}
/* Some versions of OpenSSL don't handle it correctly if not at end */
#if defined(POLARSSL_SSL_FALLBACK_SCSV)
if( ssl->fallback == SSL_IS_FALLBACK )
{
SSL_DEBUG_MSG( 3, ( "adding FALLBACK_SCSV" ) );
*p++ = (unsigned char)( SSL_FALLBACK_SCSV >> 8 );
*p++ = (unsigned char)( SSL_FALLBACK_SCSV );
n++;
}
#endif
*q++ = (unsigned char)( n >> 7 );
*q++ = (unsigned char)( n << 1 );

7
library/ssl_tls.c
View File

@ -3977,6 +3977,13 @@ void ssl_set_min_version( ssl_context *ssl, int major, int minor )
}
}
#if defined(POLARSSL_SSL_FALLBACK_SCSV) && defined(POLARSSL_SSL_CLI_C)
void ssl_set_fallback( ssl_context *ssl, char fallback )
{
ssl->fallback = fallback;
}
#endif
#if defined(POLARSSL_SSL_MAX_FRAGMENT_LENGTH)
int ssl_set_max_frag_len( ssl_context *ssl, unsigned char mfl_code )
{

24
programs/ssl/ssl_client2.c
View File

@ -95,6 +95,7 @@ int main( int argc, char *argv[] )
#define DFL_RECO_DELAY 0
#define DFL_TICKETS SSL_SESSION_TICKETS_ENABLED
#define DFL_ALPN_STRING NULL
#define DFL_FALLBACK -1
#define GET_REQUEST "GET %s HTTP/1.0\r\nExtra-header: "
#define GET_REQUEST_END "\r\n\r\n"
@ -132,6 +133,7 @@ struct options
int reco_delay; /* delay in seconds before resuming session */
int tickets; /* enable / disable session tickets */
const char *alpn_string; /* ALPN supported protocols */
int fallback; /* is this a fallback connection? */
} opt;
static void my_debug( void *ctx, int level, const char *str )
@ -284,6 +286,13 @@ static int my_verify( void *data, x509_crt *crt, int depth, int *flags )
#define USAGE_ALPN ""
#endif /* POLARSSL_SSL_ALPN */
#if defined(POLARSSL_SSL_FALLBACK_SCSV)
#define USAGE_FALLBACK \
" fallback=0/1 default: (library default: off)\n"
#else
#define USAGE_FALLBACK ""
#endif
#define USAGE \
"\n usage: ssl_client2 param=<>...\n" \
"\n acceptable parameters:\n" \
@ -313,6 +322,7 @@ static int my_verify( void *data, x509_crt *crt, int depth, int *flags )
USAGE_MAX_FRAG_LEN \
USAGE_TRUNC_HMAC \
USAGE_ALPN \
USAGE_FALLBACK \
"\n" \
" min_version=%%s default: \"\" (ssl3)\n" \
" max_version=%%s default: \"\" (tls1_2)\n" \
@ -413,6 +423,7 @@ int main( int argc, char *argv[] )
opt.reco_delay = DFL_RECO_DELAY;
opt.tickets = DFL_TICKETS;
opt.alpn_string = DFL_ALPN_STRING;
opt.fallback = DFL_FALLBACK;
for( i = 1; i < argc; i++ )
{
@ -519,6 +530,15 @@ int main( int argc, char *argv[] )
{
opt.alpn_string = q;
}
else if( strcmp( p, "fallback" ) == 0 )
{
switch( atoi( q ) )
{
case 0: opt.fallback = SSL_IS_NOT_FALLBACK; break;
case 1: opt.fallback = SSL_IS_FALLBACK; break;
default: goto usage;
}
}
else if( strcmp( p, "min_version" ) == 0 )
{
if( strcmp( q, "ssl3" ) == 0 )
@ -952,6 +972,10 @@ int main( int argc, char *argv[] )
ssl_set_min_version( &ssl, SSL_MAJOR_VERSION_3, opt.min_version );
if( opt.max_version != -1 )
ssl_set_max_version( &ssl, SSL_MAJOR_VERSION_3, opt.max_version );
#if defined(POLARSSL_SSL_FALLBACK_SCSV)
if( opt.fallback != DFL_FALLBACK )
ssl_set_fallback( &ssl, opt.fallback );
#endif
/*
* 4. Handshake

54
tests/ssl-opt.sh
View File

@ -80,6 +80,21 @@ requires_openssl_with_sslv2() {
fi
}
# skip next test if OpenSSL doesn't support FALLBACK_SCSV
requires_openssl_with_fallback_scsv() {
if [ -z "${OPENSSL_HAS_FBSCSV:-}" ]; then
if $OPENSSL_CMD s_client -help 2>&1 | grep fallback_scsv >/dev/null
then
OPENSSL_HAS_FBSCSV="YES"
else
OPENSSL_HAS_FBSCSV="NO"
fi
fi
if [ "$OPENSSL_HAS_FBSCSV" = "NO" ]; then
SKIP_NEXT="YES"
fi
}
# skip next test if GnuTLS isn't available
requires_gnutls() {
if [ -z "${GNUTLS_AVAILABLE:-}" ]; then
@ -425,6 +440,45 @@ run_test "Truncated HMAC: actual test" \
0 \
-s "dumping 'computed mac' (10 bytes)"
# Tests for FALLBACK_SCSV
run_test "Fallback SCSV: default" \
"$P_SRV" \
"$P_CLI debug_level=3 force_version=tls1_1" \
0 \
-C "adding FALLBACK_SCSV" \
-C "is a fatal alert message (msg 86)"
run_test "Fallback SCSV: explicitly disabled" \
"$P_SRV" \
"$P_CLI debug_level=3 force_version=tls1_1 fallback=0" \
0 \
-C "adding FALLBACK_SCSV" \
-C "is a fatal alert message (msg 86)"
run_test "Fallback SCSV: enabled" \
"$P_SRV" \
"$P_CLI debug_level=3 force_version=tls1_1 fallback=1" \
0 \
-c "adding FALLBACK_SCSV" \
-C "is a fatal alert message (msg 86)"
requires_openssl_with_fallback_scsv
run_test "Fallback SCSV: default, openssl server" \
"$O_SRV" \
"$P_CLI debug_level=3 force_version=tls1_1 fallback=0" \
0 \
-C "adding FALLBACK_SCSV" \
-C "is a fatal alert message (msg 86)"
requires_openssl_with_fallback_scsv
run_test "Fallback SCSV: enabled, openssl server" \
"$O_SRV" \
"$P_CLI debug_level=3 force_version=tls1_1 fallback=1" \
1 \
-c "adding FALLBACK_SCSV" \
-c "is a fatal alert message (msg 86)"
# Tests for Session Tickets
run_test "Session resume using tickets: basic" \