From 7f0a8f5060b28dc35e152d7290b583de99361d80 Mon Sep 17 00:00:00 2001
From: Sumit Bose <sbose@redhat.com>
Date: Tue, 2 Jul 2019 17:11:50 +0200
Subject: [PATCH 6/7] p11_child: prefer better digest function if card supports
 it

To improve FIPS compliance and security in general p11_child now checks
which message digest functions (hashes) are support for RSA keys and
tries to use the highest bit length supported.

For EC keys sha512 is used unconditionally.

Related to https://pagure.io/SSSD/sssd/issue/4039

Reviewed-by: Alexey Tikhonov <atikhono@redhat.com>
---
 src/p11_child/p11_child_openssl.c | 87 +++++++++++++++++++++++++++++--
 1 file changed, 82 insertions(+), 5 deletions(-)

diff --git a/src/p11_child/p11_child_openssl.c b/src/p11_child/p11_child_openssl.c
index 007f58c52..7233f39fd 100644
--- a/src/p11_child/p11_child_openssl.c
+++ b/src/p11_child/p11_child_openssl.c
@@ -1097,7 +1097,75 @@ static int rs_to_seq(TALLOC_CTX *mem_ctx, CK_BYTE *rs_sig, CK_ULONG rs_sig_len,
     return EOK;
 }
 
+static CK_RV get_preferred_rsa_mechanism(TALLOC_CTX *mem_ctx,
+                                         CK_FUNCTION_LIST *module,
+                                         CK_SLOT_ID slot_id,
+                                         CK_MECHANISM_TYPE *preferred_mechanism,
+                                         const EVP_MD **preferred_evp_md)
+{
+    CK_ULONG count;
+    CK_MECHANISM_TYPE *mechanism_list = NULL;
+    CK_RV rv;
+    size_t c;
+    size_t m;
+    struct prefs {
+        CK_MECHANISM_TYPE mech;
+        const char *mech_name;
+        const EVP_MD *evp_md;
+        const char *md_name;
+    } prefs[] = {
+        { CKM_SHA512_RSA_PKCS, "CKM_SHA512_RSA_PKCS", EVP_sha512(), "sha512" },
+        { CKM_SHA384_RSA_PKCS, "CKM_SHA384_RSA_PKCS", EVP_sha384(), "sha384" },
+        { CKM_SHA256_RSA_PKCS, "CKM_SHA256_RSA_PKCS", EVP_sha256(), "sha256" },
+        { CKM_SHA224_RSA_PKCS, "CKM_SHA224_RSA_PKCS", EVP_sha224(), "sha224" },
+        { CKM_SHA1_RSA_PKCS,   "CKM_SHA1_RSA_PKCS",   EVP_sha1(),   "sha1" },
+        { 0, NULL }
+    };
+
+    *preferred_mechanism = CKM_SHA1_RSA_PKCS;
+    *preferred_evp_md = EVP_sha1();
+
+    rv = module->C_GetMechanismList(slot_id, NULL, &count);
+    if (rv == CKR_OK && count > 0) {
+        mechanism_list = talloc_size(mem_ctx,
+                                     count * sizeof(CK_MECHANISM_TYPE));
+        if (mechanism_list != NULL) {
+            rv = module->C_GetMechanismList(slot_id, mechanism_list, &count);
+            if (rv == CKR_OK) {
+                if (DEBUG_IS_SET(SSSDBG_TRACE_ALL)) {
+                    for (m = 0; m < count; m++) {
+                        DEBUG(SSSDBG_TRACE_ALL, "Found mechanism [%lu].\n",
+                                                mechanism_list[m]);
+                    }
+                }
+                for (c = 0; prefs[c].mech != 0; c++) {
+                    for (m = 0; m < count; m++) {
+                        if (prefs[c].mech == mechanism_list[m]) {
+                            *preferred_mechanism = prefs[c].mech;
+                            *preferred_evp_md = prefs[c].evp_md;
+                            DEBUG(SSSDBG_FUNC_DATA,
+                                  "Using PKCS#11 mechanism [%lu][%s] and "
+                                  "local message digest [%s].\n",
+                                  *preferred_mechanism, prefs[c].mech_name,
+                                  prefs[c].md_name);
+                            break;
+                        }
+                    }
+                    if (m != count) {
+                        break;
+                    }
+                }
+            }
+        }
+    }
+
+    talloc_free(mechanism_list);
+
+    return rv;
+}
+
 static int sign_data(CK_FUNCTION_LIST *module, CK_SESSION_HANDLE session,
+                     CK_SLOT_ID slot_id,
                      struct cert_list *cert)
 {
     CK_OBJECT_CLASS key_class = CKO_PRIVATE_KEY;
@@ -1108,6 +1176,7 @@ static int sign_data(CK_FUNCTION_LIST *module, CK_SESSION_HANDLE session,
       {CKA_ID, NULL, 0}
     };
     CK_MECHANISM mechanism = { CK_UNAVAILABLE_INFORMATION, NULL, 0 };
+    CK_MECHANISM_TYPE preferred_mechanism;
     CK_OBJECT_HANDLE priv_key_object;
     CK_ULONG object_count;
     CK_BYTE random_value[128];
@@ -1157,15 +1226,23 @@ static int sign_data(CK_FUNCTION_LIST *module, CK_SESSION_HANDLE session,
 
     switch (get_key_type(module, session, priv_key_object)) {
     case CKK_RSA:
-        DEBUG(SSSDBG_TRACE_ALL, "Found RSA key using CKM_SHA1_RSA_PKCS.\n");
-        mechanism.mechanism = CKM_SHA1_RSA_PKCS;
-        evp_md = EVP_sha1();
+        rv = get_preferred_rsa_mechanism(cert, module, slot_id,
+                                         &preferred_mechanism, &evp_md);
+        if (rv != CKR_OK) {
+            DEBUG(SSSDBG_OP_FAILURE, "get_preferred_rsa_mechanism failed, "
+                                     "using default CKM_SHA1_RSA_PKCS.\n");
+            preferred_mechanism = CKM_SHA1_RSA_PKCS;
+            evp_md = EVP_sha1();
+        }
+        DEBUG(SSSDBG_TRACE_ALL, "Found RSA key using mechanism [%lu].\n",
+                                preferred_mechanism);
+        mechanism.mechanism = preferred_mechanism;
         card_does_hash = true;
         break;
     case CKK_EC:
         DEBUG(SSSDBG_TRACE_ALL, "Found ECC key using CKM_ECDSA.\n");
         mechanism.mechanism = CKM_ECDSA;
-        evp_md = EVP_sha1();
+        evp_md = EVP_sha512();
         card_does_hash = false;
         break;
     case CK_UNAVAILABLE_INFORMATION:
@@ -1662,7 +1739,7 @@ errno_t do_card(TALLOC_CTX *mem_ctx, struct p11_ctx *p11_ctx,
             goto done;
         }
 
-        ret = sign_data(module, session, cert_list);
+        ret = sign_data(module, session, slot_id, cert_list);
         if (ret != EOK) {
             DEBUG(SSSDBG_OP_FAILURE, "sign_data failed.\n");
             ret = EACCES;
-- 
2.20.1