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Remove NULLs in s2n_kex (#4293)
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@lrstewart
lrstewart authored Nov 20, 2023
1 parent f3e7055 commit 2482844
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Showing 4 changed files with 76 additions and 28 deletions.
4 changes: 3 additions & 1 deletion tls/s2n_auth_selection.c
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Original file line number Diff line number Diff line change
Expand Up @@ -88,7 +88,9 @@ static int s2n_is_sig_alg_valid_for_cipher_suite(s2n_signature_algorithm sig_alg
* Therefore, if a cipher suite uses a non-ephemeral kex, then any signature
* algorithm that requires RSA-PSS certificates is not valid.
*/
if (cipher_suite->key_exchange_alg != NULL && !cipher_suite->key_exchange_alg->is_ephemeral) {
const struct s2n_kex *kex = cipher_suite->key_exchange_alg;
POSIX_ENSURE_REF(kex);
if (!kex->is_ephemeral) {
POSIX_ENSURE_NE(cert_type_for_sig_alg, S2N_PKEY_TYPE_RSA_PSS);
}

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28 changes: 12 additions & 16 deletions tls/s2n_cipher_suites.c
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Original file line number Diff line number Diff line change
Expand Up @@ -698,7 +698,7 @@ struct s2n_cipher_suite s2n_tls13_aes_128_gcm_sha256 = {
.available = 0,
.name = "TLS_AES_128_GCM_SHA256",
.iana_value = { TLS_AES_128_GCM_SHA256 },
.key_exchange_alg = NULL,
.key_exchange_alg = &s2n_tls13_kex,
.auth_method = S2N_AUTHENTICATION_METHOD_TLS13,
.record_alg = NULL,
.all_record_algs = { &s2n_tls13_record_alg_aes128_gcm },
Expand All @@ -712,7 +712,7 @@ struct s2n_cipher_suite s2n_tls13_aes_256_gcm_sha384 = {
.available = 0,
.name = "TLS_AES_256_GCM_SHA384",
.iana_value = { TLS_AES_256_GCM_SHA384 },
.key_exchange_alg = NULL,
.key_exchange_alg = &s2n_tls13_kex,
.auth_method = S2N_AUTHENTICATION_METHOD_TLS13,
.record_alg = NULL,
.all_record_algs = { &s2n_tls13_record_alg_aes256_gcm },
Expand All @@ -726,7 +726,7 @@ struct s2n_cipher_suite s2n_tls13_chacha20_poly1305_sha256 = {
.available = 0,
.name = "TLS_CHACHA20_POLY1305_SHA256",
.iana_value = { TLS_CHACHA20_POLY1305_SHA256 },
.key_exchange_alg = NULL,
.key_exchange_alg = &s2n_tls13_kex,
.auth_method = S2N_AUTHENTICATION_METHOD_TLS13,
.record_alg = NULL,
.all_record_algs = { &s2n_tls13_record_alg_chacha20_poly1305 },
Expand Down Expand Up @@ -1276,19 +1276,15 @@ static int s2n_set_cipher_as_server(struct s2n_connection *conn, uint8_t *wire,
continue;
}

/* TLS 1.3 does not include key exchange in cipher suites */
if (match->minimum_required_tls_version < S2N_TLS13) {
/* If the kex is not supported continue to the next candidate */
bool kex_supported = false;
POSIX_GUARD_RESULT(s2n_kex_supported(match, conn, &kex_supported));
if (!kex_supported) {
continue;
}

/* If the kex is not configured correctly continue to the next candidate */
if (s2n_result_is_error(s2n_configure_kex(match, conn))) {
continue;
}
/* If the kex is not supported continue to the next candidate */
bool kex_supported = false;
POSIX_GUARD_RESULT(s2n_kex_supported(match, conn, &kex_supported));
if (!kex_supported) {
continue;
}
/* If the kex is not configured correctly continue to the next candidate */
if (s2n_result_is_error(s2n_configure_kex(match, conn))) {
continue;
}

/**
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71 changes: 60 additions & 11 deletions tls/s2n_kex.c
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Original file line number Diff line number Diff line change
Expand Up @@ -25,6 +25,14 @@
#include "tls/s2n_tls.h"
#include "utils/s2n_safety.h"

static S2N_RESULT s2n_check_tls13(const struct s2n_cipher_suite *cipher_suite,
struct s2n_connection *conn, bool *is_supported)
{
RESULT_ENSURE_REF(is_supported);
*is_supported = (s2n_connection_get_protocol_version(conn) >= S2N_TLS13);
return S2N_RESULT_OK;
}

static S2N_RESULT s2n_check_rsa_key(const struct s2n_cipher_suite *cipher_suite, struct s2n_connection *conn, bool *is_supported)
{
RESULT_ENSURE_REF(cipher_suite);
Expand Down Expand Up @@ -135,11 +143,6 @@ static S2N_RESULT s2n_configure_kem(const struct s2n_cipher_suite *cipher_suite,
return S2N_RESULT_OK;
}

static S2N_RESULT s2n_no_op_configure(const struct s2n_cipher_suite *cipher_suite, struct s2n_connection *conn)
{
return S2N_RESULT_OK;
}

static S2N_RESULT s2n_check_hybrid_ecdhe_kem(const struct s2n_cipher_suite *cipher_suite, struct s2n_connection *conn, bool *is_supported)
{
RESULT_ENSURE_REF(cipher_suite);
Expand All @@ -156,6 +159,34 @@ static S2N_RESULT s2n_check_hybrid_ecdhe_kem(const struct s2n_cipher_suite *ciph
return S2N_RESULT_OK;
}

static S2N_RESULT s2n_kex_configure_noop(const struct s2n_cipher_suite *cipher_suite,
struct s2n_connection *conn)
{
return S2N_RESULT_OK;
}

static int s2n_kex_server_key_recv_read_data_unimplemented(struct s2n_connection *conn,
struct s2n_blob *data_to_verify, struct s2n_kex_raw_server_data *kex_data)
{
POSIX_BAIL(S2N_ERR_UNIMPLEMENTED);
}

static int s2n_kex_server_key_recv_parse_data_unimplemented(struct s2n_connection *conn,
struct s2n_kex_raw_server_data *kex_data)
{
POSIX_BAIL(S2N_ERR_UNIMPLEMENTED);
}

static int s2n_kex_io_unimplemented(struct s2n_connection *conn, struct s2n_blob *data_to_sign)
{
POSIX_BAIL(S2N_ERR_UNIMPLEMENTED);
}

static int s2n_kex_prf_unimplemented(struct s2n_connection *conn, struct s2n_blob *premaster_secret)
{
POSIX_BAIL(S2N_ERR_UNIMPLEMENTED);
}

const struct s2n_kex s2n_kem = {
.is_ephemeral = true,
.connection_supported = &s2n_check_kem,
Expand All @@ -165,15 +196,16 @@ const struct s2n_kex s2n_kem = {
.server_key_send = &s2n_kem_server_key_send,
.client_key_recv = &s2n_kem_client_key_recv,
.client_key_send = &s2n_kem_client_key_send,
.prf = &s2n_kex_prf_unimplemented,
};

const struct s2n_kex s2n_rsa = {
.is_ephemeral = false,
.connection_supported = &s2n_check_rsa_key,
.configure_connection = &s2n_no_op_configure,
.server_key_recv_read_data = NULL,
.server_key_recv_parse_data = NULL,
.server_key_send = NULL,
.configure_connection = &s2n_kex_configure_noop,
.server_key_recv_read_data = &s2n_kex_server_key_recv_read_data_unimplemented,
.server_key_recv_parse_data = &s2n_kex_server_key_recv_parse_data_unimplemented,
.server_key_send = &s2n_kex_io_unimplemented,
.client_key_recv = &s2n_rsa_client_key_recv,
.client_key_send = &s2n_rsa_client_key_send,
.prf = &s2n_prf_calculate_master_secret,
Expand All @@ -182,7 +214,7 @@ const struct s2n_kex s2n_rsa = {
const struct s2n_kex s2n_dhe = {
.is_ephemeral = true,
.connection_supported = &s2n_check_dhe,
.configure_connection = &s2n_no_op_configure,
.configure_connection = &s2n_kex_configure_noop,
.server_key_recv_read_data = &s2n_dhe_server_key_recv_read_data,
.server_key_recv_parse_data = &s2n_dhe_server_key_recv_parse_data,
.server_key_send = &s2n_dhe_server_key_send,
Expand All @@ -194,7 +226,7 @@ const struct s2n_kex s2n_dhe = {
const struct s2n_kex s2n_ecdhe = {
.is_ephemeral = true,
.connection_supported = &s2n_check_ecdhe,
.configure_connection = &s2n_no_op_configure,
.configure_connection = &s2n_kex_configure_noop,
.server_key_recv_read_data = &s2n_ecdhe_server_key_recv_read_data,
.server_key_recv_parse_data = &s2n_ecdhe_server_key_recv_parse_data,
.server_key_send = &s2n_ecdhe_server_key_send,
Expand All @@ -216,6 +248,23 @@ const struct s2n_kex s2n_hybrid_ecdhe_kem = {
.prf = &s2n_hybrid_prf_master_secret,
};

/* TLS1.3 key exchange is implemented differently from previous versions and does
* not currently require most of the functionality offered by s2n_kex.
* This structure primarily acts as a placeholder, so its methods are either
* noops or unimplemented.
*/
const struct s2n_kex s2n_tls13_kex = {
.is_ephemeral = true,
.connection_supported = &s2n_check_tls13,
.configure_connection = &s2n_kex_configure_noop,
.server_key_recv_read_data = &s2n_kex_server_key_recv_read_data_unimplemented,
.server_key_recv_parse_data = &s2n_kex_server_key_recv_parse_data_unimplemented,
.server_key_send = &s2n_kex_io_unimplemented,
.client_key_recv = &s2n_kex_io_unimplemented,
.client_key_send = &s2n_kex_io_unimplemented,
.prf = &s2n_kex_prf_unimplemented,
};

S2N_RESULT s2n_kex_supported(const struct s2n_cipher_suite *cipher_suite, struct s2n_connection *conn, bool *is_supported)
{
RESULT_ENSURE_REF(cipher_suite);
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1 change: 1 addition & 0 deletions tls/s2n_kex.h
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Original file line number Diff line number Diff line change
Expand Up @@ -40,6 +40,7 @@ extern const struct s2n_kex s2n_rsa;
extern const struct s2n_kex s2n_dhe;
extern const struct s2n_kex s2n_ecdhe;
extern const struct s2n_kex s2n_hybrid_ecdhe_kem;
extern const struct s2n_kex s2n_tls13_kex;

S2N_RESULT s2n_kex_supported(const struct s2n_cipher_suite *cipher_suite, struct s2n_connection *conn, bool *is_supported);
S2N_RESULT s2n_configure_kex(const struct s2n_cipher_suite *cipher_suite, struct s2n_connection *conn);
Expand Down

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