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