From c63599ee9708d543205a9173207ee7167315c624 Mon Sep 17 00:00:00 2001
From: Clemens Lang <cllang@redhat.com>
Date: Tue, 1 Mar 2022 15:44:18 +0100
Subject: [PATCH] Allow SHA1 in seclevel 2 if rh-allow-sha1-signatures = yes
References: rhbz#2055796
---
crypto/x509/x509_vfy.c | 19 ++++++++++-
doc/man5/config.pod | 7 +++-
ssl/t1_lib.c | 64 ++++++++++++++++++++++++++++-------
test/recipes/25-test_verify.t | 7 ++--
4 files changed, 79 insertions(+), 18 deletions(-)
diff --git a/crypto/x509/x509_vfy.c b/crypto/x509/x509_vfy.c
index ff3ca83de6..a549c1c111 100644
--- a/crypto/x509/x509_vfy.c
+++ b/crypto/x509/x509_vfy.c
@@ -25,6 +25,7 @@
#include <openssl/objects.h>
#include <openssl/core_names.h>
#include "internal/dane.h"
+#include "internal/sslconf.h"
#include "crypto/x509.h"
#include "x509_local.h"
@@ -3440,14 +3441,30 @@ static int check_sig_level(X509_STORE_CTX *ctx, X509 *cert)
{
int secbits = -1;
int level = ctx->param->auth_level;
+ int nid;
+ OSSL_LIB_CTX *libctx = NULL;
if (level <= 0)
return 1;
if (level > NUM_AUTH_LEVELS)
level = NUM_AUTH_LEVELS;
- if (!X509_get_signature_info(cert, NULL, NULL, &secbits, NULL))
+ if (ctx->libctx)
+ libctx = ctx->libctx;
+ else if (cert->libctx)
+ libctx = cert->libctx;
+ else
+ libctx = OSSL_LIB_CTX_get0_global_default();
+
+ if (!X509_get_signature_info(cert, &nid, NULL, &secbits, NULL))
return 0;
+ if (nid == NID_sha1
+ && ossl_ctx_legacy_digest_signatures_allowed(libctx, 0)
+ && ctx->param->auth_level < 3)
+ /* When rh-allow-sha1-signatures = yes and security level <= 2,
+ * explicitly allow SHA1 for backwards compatibility. */
+ return 1;
+
return secbits >= minbits_table[level - 1];
}
diff --git a/doc/man5/config.pod b/doc/man5/config.pod
index aa1be5ca7f..aa69e2b844 100644
--- a/doc/man5/config.pod
+++ b/doc/man5/config.pod
@@ -305,7 +305,12 @@ When set to B<no>, any attempt to create or verify a signature with a SHA1
digest will fail. For compatibility with older versions of OpenSSL, set this
option to B<yes>. This setting also affects TLS, where signature algorithms
that use SHA1 as digest will no longer be supported if this option is set to
-B<no>.
+B<no>. Note that enabling B<rh-allow-sha1-signatures> will allow TLS signature
+algorithms that use SHA1 in security level 2, despite the definition of
+security level 2 of 112 bits of security, which SHA1 does not meet. Because
+TLS 1.1 or lower use MD5-SHA1 as pseudorandom function (PRF) to derive key
+material, disabling B<rh-allow-sha1-signatures> requires the use of TLS 1.2 or
+newer.
=item B<fips_mode> (deprecated)
diff --git a/ssl/t1_lib.c b/ssl/t1_lib.c
index 4b74ee1a34..5f089de107 100644
--- a/ssl/t1_lib.c
+++ b/ssl/t1_lib.c
@@ -20,6 +20,7 @@
#include <openssl/bn.h>
#include <openssl/provider.h>
#include <openssl/param_build.h>
+#include "crypto/x509.h"
#include "internal/sslconf.h"
#include "internal/nelem.h"
#include "internal/sizes.h"
@@ -1561,19 +1562,27 @@ int tls12_check_peer_sigalg(SSL *s, uint16_t sig, EVP_PKEY *pkey)
SSLfatal(s, SSL_AD_HANDSHAKE_FAILURE, SSL_R_UNKNOWN_DIGEST);
return 0;
}
- /*
- * Make sure security callback allows algorithm. For historical
- * reasons we have to pass the sigalg as a two byte char array.
- */
- sigalgstr[0] = (sig >> 8) & 0xff;
- sigalgstr[1] = sig & 0xff;
- secbits = sigalg_security_bits(s->ctx, lu);
- if (secbits == 0 ||
- !ssl_security(s, SSL_SECOP_SIGALG_CHECK, secbits,
- md != NULL ? EVP_MD_get_type(md) : NID_undef,
- (void *)sigalgstr)) {
- SSLfatal(s, SSL_AD_HANDSHAKE_FAILURE, SSL_R_WRONG_SIGNATURE_TYPE);
- return 0;
+
+ if (lu->hash == NID_sha1
+ && ossl_ctx_legacy_digest_signatures_allowed(s->ctx->libctx, 0)
+ && SSL_get_security_level(s) < 3) {
+ /* when rh-allow-sha1-signatures = yes and security level <= 2,
+ * explicitly allow SHA1 for backwards compatibility */
+ } else {
+ /*
+ * Make sure security callback allows algorithm. For historical
+ * reasons we have to pass the sigalg as a two byte char array.
+ */
+ sigalgstr[0] = (sig >> 8) & 0xff;
+ sigalgstr[1] = sig & 0xff;
+ secbits = sigalg_security_bits(s->ctx, lu);
+ if (secbits == 0 ||
+ !ssl_security(s, SSL_SECOP_SIGALG_CHECK, secbits,
+ md != NULL ? EVP_MD_get_type(md) : NID_undef,
+ (void *)sigalgstr)) {
+ SSLfatal(s, SSL_AD_HANDSHAKE_FAILURE, SSL_R_WRONG_SIGNATURE_TYPE);
+ return 0;
+ }
}
/* Store the sigalg the peer uses */
s->s3.tmp.peer_sigalg = lu;
@@ -2106,6 +2115,14 @@ static int tls12_sigalg_allowed(const SSL *s, int op, const SIGALG_LOOKUP *lu)
}
}
+ if (lu->hash == NID_sha1
+ && ossl_ctx_legacy_digest_signatures_allowed(s->ctx->libctx, 0)
+ && SSL_get_security_level(s) < 3) {
+ /* when rh-allow-sha1-signatures = yes and security level <= 2,
+ * explicitly allow SHA1 for backwards compatibility */
+ return 1;
+ }
+
/* Finally see if security callback allows it */
secbits = sigalg_security_bits(s->ctx, lu);
sigalgstr[0] = (lu->sigalg >> 8) & 0xff;
@@ -2977,6 +2994,8 @@ static int ssl_security_cert_sig(SSL *s, SSL_CTX *ctx, X509 *x, int op)
{
/* Lookup signature algorithm digest */
int secbits, nid, pknid;
+ OSSL_LIB_CTX *libctx = NULL;
+
/* Don't check signature if self signed */
if ((X509_get_extension_flags(x) & EXFLAG_SS) != 0)
return 1;
@@ -2985,6 +3004,25 @@ static int ssl_security_cert_sig(SSL *s, SSL_CTX *ctx, X509 *x, int op)
/* If digest NID not defined use signature NID */
if (nid == NID_undef)
nid = pknid;
+
+ if (x && x->libctx)
+ libctx = x->libctx;
+ else if (ctx && ctx->libctx)
+ libctx = ctx->libctx;
+ else if (s && s->ctx && s->ctx->libctx)
+ libctx = s->ctx->libctx;
+ else
+ libctx = OSSL_LIB_CTX_get0_global_default();
+
+ if (nid == NID_sha1
+ && ossl_ctx_legacy_digest_signatures_allowed(libctx, 0)
+ && ((s != NULL && SSL_get_security_level(s) < 3)
+ || (ctx != NULL && SSL_CTX_get_security_level(ctx) < 3)
+ ))
+ /* When rh-allow-sha1-signatures = yes and security level <= 2,
+ * explicitly allow SHA1 for backwards compatibility. */
+ return 1;
+
if (s)
return ssl_security(s, op, secbits, nid, x);
else
diff --git a/test/recipes/25-test_verify.t b/test/recipes/25-test_verify.t
index 700bbd849c..2de1d76b5e 100644
--- a/test/recipes/25-test_verify.t
+++ b/test/recipes/25-test_verify.t
@@ -29,7 +29,7 @@ sub verify {
run(app([@args]));
}
-plan tests => 163;
+plan tests => 162;
# Canonical success
ok(verify("ee-cert", "sslserver", ["root-cert"], ["ca-cert"]),
@@ -387,8 +387,9 @@ ok(verify("ee-pss-sha1-cert", "", ["root-cert"], ["ca-cert"], "-auth_level", "0"
ok(verify("ee-pss-sha256-cert", "", ["root-cert"], ["ca-cert"], ),
"CA with PSS signature using SHA256");
-ok(!verify("ee-pss-sha1-cert", "", ["root-cert"], ["ca-cert"], "-auth_level", "1"),
- "Reject PSS signature using SHA1 and auth level 1");
+## rh-allow-sha1-signatures=yes allows this to pass despite -auth_level 1
+#ok(!verify("ee-pss-sha1-cert", "", ["root-cert"], ["ca-cert"], "-auth_level", "1"),
+# "Reject PSS signature using SHA1 and auth level 1");
ok(verify("ee-pss-sha256-cert", "", ["root-cert"], ["ca-cert"], "-auth_level", "2"),
"PSS signature using SHA256 and auth level 2");
--
2.35.1