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Add mbedtls_ssl_get_max_frag_len()

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This is not very useful for TLS as mbedtls_ssl_write() will automatically
fragment and return the length used, and the application should check for that
anyway, but this is useful for DTLS where mbedtls_ssl_write() returns an
error, and the application needs to be able to query the maximum length
instead of just guessing.
This commit is contained in:
Manuel Pégourié-Gonnard 2015-08-31 18:30:52 +02:00
parent 7b23c51595
commit a2cda6bfaf
6 changed files with 69 additions and 17 deletions
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2
ChangeLog
View file

@ -37,6 +37,8 @@ Changes
compiler's command line.
* Prepend a "thread identifier" to debug messages (issue pointed out by
Hugo Leisink) (#210).
* Add mbedtls_ssl_get_max_frag_len() to query the current maximum fragment
length.
= mbed TLS 2.0.0 released 2015-07-13

20
include/mbedtls/ssl.h
View file

@ -2027,6 +2027,26 @@ const char *mbedtls_ssl_get_version( const mbedtls_ssl_context *ssl );
*/
int mbedtls_ssl_get_record_expansion( const mbedtls_ssl_context *ssl );
#if defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH)
/**
* \brief Return the maximum fragment length (payload, in bytes).
* This is the value negotiated with peer if any,
* or the locally configured value.
*
* \note With DTLS, \c mbedtls_ssl_write() will return an error if
* called with a larger length value.
* With TLS, \c mbedtls_ssl_write() will fragment the input if
* necessary and return the number of bytes written; it is up
* to the caller to call \c mbedtls_ssl_write() again in
* order to send the remaining bytes if any.
*
* \param ssl SSL context
*
* \return Current maximum fragment length.
*/
size_t mbedtls_ssl_get_max_frag_len( const mbedtls_ssl_context *ssl );
#endif /* MBEDTLS_SSL_MAX_FRAGMENT_LENGTH */
#if defined(MBEDTLS_X509_CRT_PARSE_C)
/**
* \brief Return the peer certificate from the current connection

41
library/ssl_tls.c
View file

@ -5862,6 +5862,29 @@ int mbedtls_ssl_get_record_expansion( const mbedtls_ssl_context *ssl )
return( (int)( mbedtls_ssl_hdr_len( ssl ) + transform_expansion ) );
}
#if defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH)
size_t mbedtls_ssl_get_max_frag_len( const mbedtls_ssl_context *ssl )
{
size_t max_len;
/*
* Assume mfl_code is correct since it was checked when set
*/
max_len = mfl_code_to_length[ssl->conf->mfl_code];
/*
* Check if a smaller max length was negotiated
*/
if( ssl->session_out != NULL &&
mfl_code_to_length[ssl->session_out->mfl_code] < max_len )
{
max_len = mfl_code_to_length[ssl->session_out->mfl_code];
}
return max_len;
}
#endif /* MBEDTLS_SSL_MAX_FRAGMENT_LENGTH */
#if defined(MBEDTLS_X509_CRT_PARSE_C)
const mbedtls_x509_crt *mbedtls_ssl_get_peer_cert( const mbedtls_ssl_context *ssl )
{
@ -6339,23 +6362,7 @@ static int ssl_write_real( mbedtls_ssl_context *ssl,
{
int ret;
#if defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH)
unsigned int max_len;
#endif
#if defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH)
/*
* Assume mfl_code is correct since it was checked when set
*/
max_len = mfl_code_to_length[ssl->conf->mfl_code];
/*
* Check if a smaller max length was negotiated
*/
if( ssl->session_out != NULL &&
mfl_code_to_length[ssl->session_out->mfl_code] < max_len )
{
max_len = mfl_code_to_length[ssl->session_out->mfl_code];
}
size_t max_len = mbedtls_ssl_get_max_frag_len( ssl );
if( len > max_len )
{

5
programs/ssl/ssl_client2.c
View file

@ -1240,6 +1240,11 @@ int main( int argc, char *argv[] )
else
mbedtls_printf( " [ Record expansion is unknown (compression) ]\n" );
#if defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH)
mbedtls_printf( " [ Maximum fragment length is %u ]\n",
(unsigned int) mbedtls_ssl_get_max_frag_len( &ssl ) );
#endif
#if defined(MBEDTLS_SSL_ALPN)
if( opt.alpn_string != NULL )
{

5
programs/ssl/ssl_server2.c
View file

@ -1946,6 +1946,11 @@ reset:
else
mbedtls_printf( " [ Record expansion is unknown (compression) ]\n" );
#if defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH)
mbedtls_printf( " [ Maximum fragment length is %u ]\n",
(unsigned int) mbedtls_ssl_get_max_frag_len( &ssl ) );
#endif
#if defined(MBEDTLS_SSL_ALPN)
if( opt.alpn_string != NULL )
{

13
tests/ssl-opt.sh
View file

@ -1085,6 +1085,8 @@ run_test "Max fragment length: not used, reference" \
"$P_SRV debug_level=3" \
"$P_CLI debug_level=3" \
0 \
-c "Maximum fragment length is 16384" \
-s "Maximum fragment length is 16384" \
-C "client hello, adding max_fragment_length extension" \
-S "found max fragment length extension" \
-S "server hello, max_fragment_length extension" \
@ -1094,6 +1096,8 @@ run_test "Max fragment length: used by client" \
"$P_SRV debug_level=3" \
"$P_CLI debug_level=3 max_frag_len=4096" \
0 \
-c "Maximum fragment length is 4096" \
-s "Maximum fragment length is 4096" \
-c "client hello, adding max_fragment_length extension" \
-s "found max fragment length extension" \
-s "server hello, max_fragment_length extension" \
@ -1103,6 +1107,8 @@ run_test "Max fragment length: used by server" \
"$P_SRV debug_level=3 max_frag_len=4096" \
"$P_CLI debug_level=3" \
0 \
-c "Maximum fragment length is 16384" \
-s "Maximum fragment length is 4096" \
-C "client hello, adding max_fragment_length extension" \
-S "found max fragment length extension" \
-S "server hello, max_fragment_length extension" \
@ -1113,6 +1119,7 @@ run_test "Max fragment length: gnutls server" \
"$G_SRV" \
"$P_CLI debug_level=3 max_frag_len=4096" \
0 \
-c "Maximum fragment length is 4096" \
-c "client hello, adding max_fragment_length extension" \
-c "found max_fragment_length extension"
@ -1120,6 +1127,8 @@ run_test "Max fragment length: client, message just fits" \
"$P_SRV debug_level=3" \
"$P_CLI debug_level=3 max_frag_len=2048 request_size=2048" \
0 \
-c "Maximum fragment length is 2048" \
-s "Maximum fragment length is 2048" \
-c "client hello, adding max_fragment_length extension" \
-s "found max fragment length extension" \
-s "server hello, max_fragment_length extension" \
@ -1131,6 +1140,8 @@ run_test "Max fragment length: client, larger message" \
"$P_SRV debug_level=3" \
"$P_CLI debug_level=3 max_frag_len=2048 request_size=2345" \
0 \
-c "Maximum fragment length is 2048" \
-s "Maximum fragment length is 2048" \
-c "client hello, adding max_fragment_length extension" \
-s "found max fragment length extension" \
-s "server hello, max_fragment_length extension" \
@ -1143,6 +1154,8 @@ run_test "Max fragment length: DTLS client, larger message" \
"$P_SRV debug_level=3 dtls=1" \
"$P_CLI debug_level=3 dtls=1 max_frag_len=2048 request_size=2345" \
1 \
-c "Maximum fragment length is 2048" \
-s "Maximum fragment length is 2048" \
-c "client hello, adding max_fragment_length extension" \
-s "found max fragment length extension" \
-s "server hello, max_fragment_length extension" \