Add new cipherlist-setting APIs that reject nonsense.
The new APIs are SSL_CTX_set_strict_cipher_list() and
SSL_set_strict_cipher_list(). They have two motivations:
First, typos in cipher lists can go undetected for a long time, and
can have surprising consequences when silently ignored.
Second, there is a tendency to use superstition in the construction of
cipher lists, for example by "turning off" things that do not actually
exist. This leads to the corrosive belief that DEFAULT and ALL ought
not to be trusted. This belief is false.
Change-Id: I42909b69186e0b4cf45457e5c0bc968f6bbf231a
Reviewed-on: https://boringssl-review.googlesource.com/13925
Commit-Queue: Matt Braithwaite <mab@google.com>
Reviewed-by: Matt Braithwaite <mab@google.com>
diff --git a/fuzz/client.cc b/fuzz/client.cc
index 860ed68..2b91e7c 100644
--- a/fuzz/client.cc
+++ b/fuzz/client.cc
@@ -279,7 +279,7 @@
SSL_set_alpn_protos(client, kALPNProtocols, sizeof(kALPNProtocols));
// Enable ciphers that are off by default.
- SSL_set_cipher_list(client, "ALL:NULL-SHA");
+ SSL_set_strict_cipher_list(client, "ALL:NULL-SHA");
BIO_write(in, buf, len);
if (SSL_do_handshake(client) == 1) {
diff --git a/fuzz/server.cc b/fuzz/server.cc
index 1ee2ec9..9cdfad9 100644
--- a/fuzz/server.cc
+++ b/fuzz/server.cc
@@ -274,7 +274,7 @@
SSL_set_tls_channel_id_enabled(server, 1);
// Enable ciphers that are off by default.
- SSL_set_cipher_list(server, "ALL:NULL-SHA");
+ SSL_set_strict_cipher_list(server, "ALL:NULL-SHA");
DH *dh = DH_get_1024_160(nullptr);
SSL_set_tmp_dh(server, dh);
diff --git a/fuzz/ssl_ctx_api.cc b/fuzz/ssl_ctx_api.cc
index b721c6b..60058fa 100644
--- a/fuzz/ssl_ctx_api.cc
+++ b/fuzz/ssl_ctx_api.cc
@@ -344,11 +344,14 @@
if (!GetString(&ciphers, cbs)) {
return;
}
- SSL_CTX_set_cipher_list(ctx, ciphers.c_str());
+ SSL_CTX_set_strict_cipher_list(ctx, ciphers.c_str());
},
[](SSL_CTX *ctx, CBS *cbs) {
- // This function was left blank rather than removed to avoid invalidating
- // the existing corpus. New entries may reuse it.
+ std::string ciphers;
+ if (!GetString(&ciphers, cbs)) {
+ return;
+ }
+ SSL_CTX_set_cipher_list(ctx, ciphers.c_str());
},
[](SSL_CTX *ctx, CBS *cbs) {
// This function was left blank rather than removed to avoid invalidating
diff --git a/include/openssl/ssl.h b/include/openssl/ssl.h
index 23e5e9b..e38e23c 100644
--- a/include/openssl/ssl.h
+++ b/include/openssl/ssl.h
@@ -1313,7 +1313,9 @@
* |TLSv1_2| matches ciphers new in TLS 1.2. This is confusing and should not
* be used.
*
- * Unknown rules silently match nothing.
+ * Unknown rules are silently ignored by legacy APIs, and rejected by APIs with
+ * "strict" in the name, which should be preferred. Cipher lists can be long and
+ * it's easy to commit typos.
*
* The special |@STRENGTH| directive will sort all enabled ciphers by strength.
*
@@ -1342,12 +1344,29 @@
* substituted when a cipher string starts with 'DEFAULT'. */
#define SSL_DEFAULT_CIPHER_LIST "ALL"
+/* SSL_CTX_set_strict_cipher_list configures the cipher list for |ctx|,
+ * evaluating |str| as a cipher string and returning error if |str| contains
+ * anything meaningless. It returns one on success and zero on failure. */
+OPENSSL_EXPORT int SSL_CTX_set_strict_cipher_list(SSL_CTX *ctx,
+ const char *str);
+
/* SSL_CTX_set_cipher_list configures the cipher list for |ctx|, evaluating
- * |str| as a cipher string. It returns one on success and zero on failure. */
+ * |str| as a cipher string. It returns one on success and zero on failure.
+ *
+ * Prefer to use |SSL_CTX_set_strict_cipher_list|. This function tolerates
+ * garbage inputs, unless an empty cipher list results. */
OPENSSL_EXPORT int SSL_CTX_set_cipher_list(SSL_CTX *ctx, const char *str);
+/* SSL_set_strict_cipher_list configures the cipher list for |ssl|, evaluating
+ * |str| as a cipher string and returning error if |str| contains anything
+ * meaningless. It returns one on success and zero on failure. */
+OPENSSL_EXPORT int SSL_set_strict_cipher_list(SSL *ssl, const char *str);
+
/* SSL_set_cipher_list configures the cipher list for |ssl|, evaluating |str| as
- * a cipher string. It returns one on success and zero on failure. */
+ * a cipher string. It returns one on success and zero on failure.
+ *
+ * Prefer to use |SSL_set_strict_cipher_list|. This function tolerates garbage
+ * inputs, unless an empty cipher list results. */
OPENSSL_EXPORT int SSL_set_cipher_list(SSL *ssl, const char *str);
/* SSL_get_ciphers returns the cipher list for |ssl|, in order of preference. */
diff --git a/ssl/internal.h b/ssl/internal.h
index b2c9fcd..a6dfad5 100644
--- a/ssl/internal.h
+++ b/ssl/internal.h
@@ -227,12 +227,13 @@
/* ssl_create_cipher_list evaluates |rule_str| according to the ciphers in
* |ssl_method|. It sets |*out_cipher_list| to a newly-allocated
* |ssl_cipher_preference_list_st| containing the result. It returns
- * |(*out_cipher_list)->ciphers| on success and NULL on
- * failure. */
+ * |(*out_cipher_list)->ciphers| on success and NULL on failure. If |strict| is
+ * true, nonsense will be rejected. If false, nonsense will be silently
+ * ignored. */
STACK_OF(SSL_CIPHER) *
ssl_create_cipher_list(const SSL_PROTOCOL_METHOD *ssl_method,
struct ssl_cipher_preference_list_st **out_cipher_list,
- const char *rule_str);
+ const char *rule_str, int strict);
/* ssl_cipher_get_value returns the cipher suite id of |cipher|. */
uint16_t ssl_cipher_get_value(const SSL_CIPHER *cipher);
diff --git a/ssl/ssl_cipher.c b/ssl/ssl_cipher.c
index 8f1ad73..52ea804 100644
--- a/ssl/ssl_cipher.c
+++ b/ssl/ssl_cipher.c
@@ -1070,7 +1070,7 @@
static int ssl_cipher_process_rulestr(const SSL_PROTOCOL_METHOD *ssl_method,
const char *rule_str,
CIPHER_ORDER **head_p,
- CIPHER_ORDER **tail_p) {
+ CIPHER_ORDER **tail_p, int strict) {
uint32_t alg_mkey, alg_auth, alg_enc, alg_mac;
uint16_t min_version;
const char *l, *buf;
@@ -1206,6 +1206,10 @@
}
if (j == kCipherAliasesLen) {
skip_rule = 1;
+ if (strict) {
+ OPENSSL_PUT_ERROR(SSL, SSL_R_INVALID_COMMAND);
+ return 0;
+ }
}
}
@@ -1253,7 +1257,7 @@
STACK_OF(SSL_CIPHER) *
ssl_create_cipher_list(const SSL_PROTOCOL_METHOD *ssl_method,
struct ssl_cipher_preference_list_st **out_cipher_list,
- const char *rule_str) {
+ const char *rule_str, int strict) {
STACK_OF(SSL_CIPHER) *cipherstack = NULL;
CIPHER_ORDER *co_list = NULL, *head = NULL, *tail = NULL, *curr;
uint8_t *in_group_flags = NULL;
@@ -1334,7 +1338,7 @@
const char *rule_p = rule_str;
if (strncmp(rule_str, "DEFAULT", 7) == 0) {
if (!ssl_cipher_process_rulestr(ssl_method, SSL_DEFAULT_CIPHER_LIST, &head,
- &tail)) {
+ &tail, strict)) {
goto err;
}
rule_p += 7;
@@ -1344,7 +1348,7 @@
}
if (*rule_p != '\0' &&
- !ssl_cipher_process_rulestr(ssl_method, rule_p, &head, &tail)) {
+ !ssl_cipher_process_rulestr(ssl_method, rule_p, &head, &tail, strict)) {
goto err;
}
diff --git a/ssl/ssl_lib.c b/ssl/ssl_lib.c
index d0151bb..e37f9f9 100644
--- a/ssl/ssl_lib.c
+++ b/ssl/ssl_lib.c
@@ -277,7 +277,7 @@
}
ssl_create_cipher_list(ret->method, &ret->cipher_list,
- SSL_DEFAULT_CIPHER_LIST);
+ SSL_DEFAULT_CIPHER_LIST, 1 /* strict */);
if (ret->cipher_list == NULL ||
sk_SSL_CIPHER_num(ret->cipher_list->ciphers) <= 0) {
OPENSSL_PUT_ERROR(SSL, SSL_R_LIBRARY_HAS_NO_CIPHERS);
@@ -1506,7 +1506,25 @@
int SSL_CTX_set_cipher_list(SSL_CTX *ctx, const char *str) {
STACK_OF(SSL_CIPHER) *cipher_list =
- ssl_create_cipher_list(ctx->method, &ctx->cipher_list, str);
+ ssl_create_cipher_list(ctx->method, &ctx->cipher_list, str,
+ 0 /* not strict */);
+ if (cipher_list == NULL) {
+ return 0;
+ }
+
+ /* |ssl_create_cipher_list| may succeed but return an empty cipher list. */
+ if (sk_SSL_CIPHER_num(cipher_list) == 0) {
+ OPENSSL_PUT_ERROR(SSL, SSL_R_NO_CIPHER_MATCH);
+ return 0;
+ }
+
+ return 1;
+}
+
+int SSL_CTX_set_strict_cipher_list(SSL_CTX *ctx, const char *str) {
+ STACK_OF(SSL_CIPHER) *cipher_list =
+ ssl_create_cipher_list(ctx->method, &ctx->cipher_list, str,
+ 1 /* strict */);
if (cipher_list == NULL) {
return 0;
}
@@ -1522,7 +1540,25 @@
int SSL_set_cipher_list(SSL *ssl, const char *str) {
STACK_OF(SSL_CIPHER) *cipher_list =
- ssl_create_cipher_list(ssl->ctx->method, &ssl->cipher_list, str);
+ ssl_create_cipher_list(ssl->ctx->method, &ssl->cipher_list, str,
+ 0 /* not strict */);
+ if (cipher_list == NULL) {
+ return 0;
+ }
+
+ /* |ssl_create_cipher_list| may succeed but return an empty cipher list. */
+ if (sk_SSL_CIPHER_num(cipher_list) == 0) {
+ OPENSSL_PUT_ERROR(SSL, SSL_R_NO_CIPHER_MATCH);
+ return 0;
+ }
+
+ return 1;
+}
+
+int SSL_set_strict_cipher_list(SSL *ssl, const char *str) {
+ STACK_OF(SSL_CIPHER) *cipher_list =
+ ssl_create_cipher_list(ssl->ctx->method, &ssl->cipher_list, str,
+ 1 /* strict */);
if (cipher_list == NULL) {
return 0;
}
diff --git a/ssl/ssl_test.cc b/ssl/ssl_test.cc
index 4e0c274..97bcab3 100644
--- a/ssl/ssl_test.cc
+++ b/ssl/ssl_test.cc
@@ -59,6 +59,8 @@
const char *rule;
// The list of expected ciphers, in order.
std::vector<ExpectedCipher> expected;
+ // True if this cipher list should fail in strict mode.
+ bool strict_fail;
};
struct CurveTest {
@@ -81,6 +83,7 @@
{TLS1_CK_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256, 0},
{TLS1_CK_ECDHE_RSA_WITH_AES_128_GCM_SHA256, 0},
},
+ false,
},
// + reorders selected ciphers to the end, keeping their relative order.
{
@@ -95,6 +98,7 @@
{TLS1_CK_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256, 0},
{TLS1_CK_ECDHE_RSA_WITH_AES_128_GCM_SHA256, 0},
},
+ false,
},
// ! banishes ciphers from future selections.
{
@@ -107,6 +111,7 @@
{TLS1_CK_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256, 0},
{TLS1_CK_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256, 0},
},
+ false,
},
// Multiple masks can be ANDed in a single rule.
{
@@ -114,6 +119,7 @@
{
{TLS1_CK_RSA_WITH_AES_128_GCM_SHA256, 0},
},
+ false,
},
// - removes selected ciphers, but preserves their order for future
// selections. Select AES_128_GCM, but order the key exchanges RSA, DHE_RSA,
@@ -126,20 +132,37 @@
{TLS1_CK_DHE_RSA_WITH_AES_128_GCM_SHA256, 0},
{TLS1_CK_ECDHE_RSA_WITH_AES_128_GCM_SHA256, 0},
},
+ false,
},
- // Unknown selectors are no-ops.
+ // Unknown selectors are no-ops, except in strict mode.
{
"ECDHE-ECDSA-CHACHA20-POLY1305:"
"ECDHE-RSA-CHACHA20-POLY1305:"
"ECDHE-ECDSA-AES128-GCM-SHA256:"
"ECDHE-RSA-AES128-GCM-SHA256:"
- "BOGUS1:-BOGUS2:+BOGUS3:!BOGUS4",
+ "BOGUS1",
{
{TLS1_CK_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256, 0},
{TLS1_CK_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256, 0},
{TLS1_CK_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256, 0},
{TLS1_CK_ECDHE_RSA_WITH_AES_128_GCM_SHA256, 0},
},
+ true,
+ },
+ // Unknown selectors are no-ops, except in strict mode.
+ {
+ "ECDHE-ECDSA-CHACHA20-POLY1305:"
+ "ECDHE-RSA-CHACHA20-POLY1305:"
+ "ECDHE-ECDSA-AES128-GCM-SHA256:"
+ "ECDHE-RSA-AES128-GCM-SHA256:"
+ "-BOGUS2:+BOGUS3:!BOGUS4",
+ {
+ {TLS1_CK_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256, 0},
+ {TLS1_CK_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256, 0},
+ {TLS1_CK_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256, 0},
+ {TLS1_CK_ECDHE_RSA_WITH_AES_128_GCM_SHA256, 0},
+ },
+ true,
},
// Square brackets specify equi-preference groups.
{
@@ -152,13 +175,14 @@
{TLS1_CK_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256, 0},
{TLS1_CK_ECDHE_RSA_WITH_AES_128_GCM_SHA256, 0},
},
+ false,
},
// @STRENGTH performs a stable strength-sort of the selected ciphers and
// only the selected ciphers.
{
// To simplify things, banish all but {ECDHE_RSA,RSA} x
// {CHACHA20,AES_256_CBC,AES_128_CBC} x SHA1.
- "!kEDH:!AESGCM:!3DES:!SHA256:!MD5:!SHA384:"
+ "!kEDH:!AESGCM:!3DES:!SHA256:!SHA384:"
// Order some ciphers backwards by strength.
"ALL:-CHACHA20:-AES256:-AES128:-ALL:"
// Select ECDHE ones and sort them by strength. Ties should resolve
@@ -174,6 +198,7 @@
{TLS1_CK_RSA_WITH_AES_128_SHA, 0},
{TLS1_CK_RSA_WITH_AES_256_SHA, 0},
},
+ false,
},
// Exact ciphers may not be used in multi-part rules; they are treated
// as unknown aliases.
@@ -186,6 +211,7 @@
{TLS1_CK_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256, 0},
{TLS1_CK_ECDHE_RSA_WITH_AES_128_GCM_SHA256, 0},
},
+ true,
},
// SSLv3 matches everything that existed before TLS 1.2.
{
@@ -193,6 +219,7 @@
{
{TLS1_CK_RSA_WITH_AES_128_SHA256, 0},
},
+ false,
},
// TLSv1.2 matches everything added in TLS 1.2.
{
@@ -200,14 +227,17 @@
{
{TLS1_CK_RSA_WITH_AES_128_SHA, 0},
},
+ false,
},
- // The two directives have no intersection.
+ // The two directives have no intersection. But each component is valid, so
+ // even in strict mode it is accepted.
{
"AES128-SHA:AES128-SHA256:!TLSv1.2+SSLv3",
{
{TLS1_CK_RSA_WITH_AES_128_SHA, 0},
{TLS1_CK_RSA_WITH_AES_128_SHA256, 0},
},
+ false,
},
};
@@ -239,8 +269,6 @@
static const char *kMustNotIncludeNull[] = {
"ALL",
"DEFAULT",
- "ALL:!eNULL",
- "ALL:!NULL",
"HIGH",
"FIPS",
"SHA",
@@ -309,6 +337,12 @@
return false;
}
+ if (!SSL_CTX_set_strict_cipher_list(ctx.get(), t.rule) != t.strict_fail) {
+ fprintf(stderr, "Unexpected strict failure result testing cipher rule '%s':"
+ " expected %d\n", t.rule, t.strict_fail);
+ return false;
+ }
+
// Compare the two lists.
if (sk_SSL_CIPHER_num(ctx->cipher_list->ciphers) != t.expected.size()) {
fprintf(stderr, "Error: cipher rule '%s' evaluated to:\n", t.rule);
@@ -335,7 +369,7 @@
if (!ctx) {
return false;
}
- if (!SSL_CTX_set_cipher_list(ctx.get(), rule)) {
+ if (!SSL_CTX_set_strict_cipher_list(ctx.get(), rule)) {
fprintf(stderr, "Error: cipher rule '%s' failed\n", rule);
return false;
}
@@ -875,7 +909,7 @@
// Set a one-element cipher list so the baseline ClientHello is unpadded.
bssl::UniquePtr<SSL> ssl(SSL_new(ctx.get()));
if (!ssl || !SSL_set_session(ssl.get(), session.get()) ||
- !SSL_set_cipher_list(ssl.get(), "ECDHE-RSA-AES128-GCM-SHA256") ||
+ !SSL_set_strict_cipher_list(ssl.get(), "ECDHE-RSA-AES128-GCM-SHA256") ||
!SSL_set_max_proto_version(ssl.get(), max_version)) {
return 0;
}
@@ -1760,7 +1794,7 @@
!SSL_CTX_set_max_proto_version(ctx.get(), version) ||
// Our default cipher list varies by CPU capabilities, so manually place
// the ChaCha20 ciphers in front.
- !SSL_CTX_set_cipher_list(ctx.get(), "CHACHA20:ALL")) {
+ !SSL_CTX_set_strict_cipher_list(ctx.get(), "CHACHA20:ALL")) {
return false;
}
diff --git a/ssl/test/bssl_shim.cc b/ssl/test/bssl_shim.cc
index dd61ffb..48d0538 100644
--- a/ssl/test/bssl_shim.cc
+++ b/ssl/test/bssl_shim.cc
@@ -927,7 +927,7 @@
cipher_list = config->cipher;
SSL_CTX_set_options(ssl_ctx.get(), SSL_OP_CIPHER_SERVER_PREFERENCE);
}
- if (!SSL_CTX_set_cipher_list(ssl_ctx.get(), cipher_list.c_str())) {
+ if (!SSL_CTX_set_strict_cipher_list(ssl_ctx.get(), cipher_list.c_str())) {
return nullptr;
}
diff --git a/tool/ciphers.cc b/tool/ciphers.cc
index f52527b..6370b78 100644
--- a/tool/ciphers.cc
+++ b/tool/ciphers.cc
@@ -32,7 +32,7 @@
const std::string &ciphers_string = args.back();
bssl::UniquePtr<SSL_CTX> ctx(SSL_CTX_new(SSLv23_client_method()));
- if (!SSL_CTX_set_cipher_list(ctx.get(), ciphers_string.c_str())) {
+ if (!SSL_CTX_set_strict_cipher_list(ctx.get(), ciphers_string.c_str())) {
fprintf(stderr, "Failed to parse cipher suite config.\n");
ERR_print_errors_fp(stderr);
return false;
diff --git a/tool/client.cc b/tool/client.cc
index 8e0ef2d..6cd40fb 100644
--- a/tool/client.cc
+++ b/tool/client.cc
@@ -277,7 +277,7 @@
}
if (args_map.count("-cipher") != 0 &&
- !SSL_CTX_set_cipher_list(ctx.get(), args_map["-cipher"].c_str())) {
+ !SSL_CTX_set_strict_cipher_list(ctx.get(), args_map["-cipher"].c_str())) {
fprintf(stderr, "Failed setting cipher list\n");
return false;
}
diff --git a/tool/server.cc b/tool/server.cc
index f203df1..20c913c 100644
--- a/tool/server.cc
+++ b/tool/server.cc
@@ -188,7 +188,7 @@
}
if (args_map.count("-cipher") != 0 &&
- !SSL_CTX_set_cipher_list(ctx.get(), args_map["-cipher"].c_str())) {
+ !SSL_CTX_set_strict_cipher_list(ctx.get(), args_map["-cipher"].c_str())) {
fprintf(stderr, "Failed setting cipher list\n");
return false;
}
