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tpm2.0-tools/0002-kdfa-use-openssl-for-hmac-not-tpm.patch
Matthias Gerstner 00ea3cc493 - 0002-kdfa-use-openssl-for-hmac-not-tpm.patch: fixed unexpected leak of 
cleartext password into the tpm when generating an HMAC in the context of
  tpm_kdfa() (key derivation function).

OBS-URL: https://build.opensuse.org/package/show/security/tpm2.0-tools?expand=0&rev=23
2017-06-29 09:49:42 +00:00

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From c5d72beaab1cbbbe68271f4bc4b6670d69985157 Mon Sep 17 00:00:00 2001
From: William Roberts <william.c.roberts@intel.com>
Date: Wed, 21 Jun 2017 09:32:32 -0700
Subject: [PATCH] kdfa: use openssl for hmac not tpm
While not reachable in the current code base tools, a potential
security bug lurked in tpm_kdfa().
If using that routine for an hmac authorization, the hmac was
calculated using the tpm. A user of an object wishing to
authenticate via hmac, would expect that the password is never
sent to the tpm. However, since the hmac calculation relies on
password, and is performed by the tpm, the password ends up
being sent in plain text to the tpm.
The fix is to use openssl to generate the hmac on the host.
Fixes: CVE-2017-7524
Signed-off-by: William Roberts <william.c.roberts@intel.com>
---
Makefile.am | 4 +--
configure.ac | 3 ++-
lib/tpm_kdfa.c | 76 +++++++++++++++++++++++++++++++++++++++++++++++--------
lib/tpm_kdfa.h | 2 +-
lib/tpm_session.c | 2 +-
5 files changed, 72 insertions(+), 15 deletions(-)
Index: tpm2.0-tools-2.0.0/Makefile.am
===================================================================
--- tpm2.0-tools-2.0.0.orig/Makefile.am
+++ tpm2.0-tools-2.0.0/Makefile.am
@@ -35,10 +35,10 @@ ACLOCAL_AMFLAGS = -I m4
INCLUDE_DIRS = -I$(srcdir)/src -I$(srcdir)/lib
LIB_COMMON := lib/libcommon.a
-AM_CFLAGS := $(INCLUDE_DIRS) $(TPM20_TSS_CFLAGS) $(EXTRA_CFLAGS)
+AM_CFLAGS := $(INCLUDE_DIRS) $(TPM20_TSS_CFLAGS) $(EXTRA_CFLAGS) $(CRYPTO_FLAGS)
AM_LDFLAGS := $(EXTRA_LDFLAGS)
-LDADD = $(LIB_COMMON) $(TPM20_TSS_LIBS) $(TCTI_SOCK_LIBS) $(TCTI_DEV_LIBS)
+LDADD = $(LIB_COMMON) $(TPM20_TSS_LIBS) $(TCTI_SOCK_LIBS) $(TCTI_DEV_LIBS) $(CRYPTO_LIBS)
sbin_PROGRAMS = \
tools/tpm2_create \
Index: tpm2.0-tools-2.0.0/configure.ac
===================================================================
--- tpm2.0-tools-2.0.0.orig/configure.ac
+++ tpm2.0-tools-2.0.0/configure.ac
@@ -49,7 +49,8 @@ AS_IF(
[AC_MSG_ERROR(
[no TCTIs: at least one TCTI library must be enabled],
[1])])
-PKG_CHECK_MODULES([CURL],[libcurl libcrypto])
+PKG_CHECK_MODULES([CRYPTO],[libcrypto])
+PKG_CHECK_MODULES([CURL],[libcurl])
AC_ARG_ENABLE([unit],
[AS_HELP_STRING([--enable-unit],
[build cmocka unit tests (default is no)])],
Index: tpm2.0-tools-2.0.0/lib/tpm_kdfa.c
===================================================================
--- tpm2.0-tools-2.0.0.orig/lib/tpm_kdfa.c
+++ tpm2.0-tools-2.0.0/lib/tpm_kdfa.c
@@ -27,20 +27,40 @@
#include <sapi/tpm20.h>
+ #include <openssl/err.h>
+#include <openssl/hmac.h>
+
#include "string-bytes.h"
#include "tpm_hmac.h"
+#include "log.h"
+
+static const EVP_MD *tpm_algorithm_to_openssl_digest(TPMI_ALG_HASH algorithm) {
-TPM_RC tpm_kdfa(TSS2_SYS_CONTEXT *sapi_context, TPMI_ALG_HASH hashAlg,
+ switch(algorithm) {
+ case TPM_ALG_SHA1:
+ return EVP_sha1();
+ case ALG_SHA256_VALUE:
+ return EVP_sha256();
+ case TPM_ALG_SHA384:
+ return EVP_sha384();
+ case TPM_ALG_SHA512:
+ return EVP_sha512();
+ default:
+ return NULL;
+ }
+ /* no return, not possible */
+}
+
+TPM_RC tpm_kdfa(TPMI_ALG_HASH hashAlg,
TPM2B *key, char *label, TPM2B *contextU, TPM2B *contextV, UINT16 bits,
TPM2B_MAX_BUFFER *resultKey )
{
- TPM2B_DIGEST tmpResult;
TPM2B_DIGEST tpm2bLabel, tpm2bBits, tpm2b_i_2;
UINT8 *tpm2bBitsPtr = &tpm2bBits.t.buffer[0];
UINT8 *tpm2b_i_2Ptr = &tpm2b_i_2.t.buffer[0];
TPM2B_DIGEST *bufferList[8];
UINT32 bitsSwizzled, i_Swizzled;
- TPM_RC rval;
+ TPM_RC rval = TPM_RC_SUCCESS;
int i, j;
UINT16 bytes = bits / 8;
@@ -64,8 +84,24 @@ TPM_RC tpm_kdfa(TSS2_SYS_CONTEXT *sapi_c
i = 1;
+ const EVP_MD *md = tpm_algorithm_to_openssl_digest(hashAlg);
+ if (!md) {
+ LOG_ERR("Algorithm not supported for hmac: %x", hashAlg);
+ return TPM_RC_HASH;
+ }
+
+ HMAC_CTX ctx;
+ HMAC_CTX_init(&ctx);
+ int rc = HMAC_Init_ex(&ctx, key->buffer, key->size, md, NULL);
+ if (!rc) {
+ LOG_ERR("HMAC Init failed: %s", ERR_error_string(rc, NULL));
+ return TPM_RC_MEMORY;
+ }
+
+ // TODO Why is this a loop? It appears to only execute once.
while( resultKey->t.size < bytes )
{
+ TPM2B_DIGEST tmpResult;
// Inner loop
i_Swizzled = string_bytes_endian_convert_32( i );
@@ -77,21 +113,41 @@ TPM_RC tpm_kdfa(TSS2_SYS_CONTEXT *sapi_c
bufferList[j++] = (TPM2B_DIGEST *)contextU;
bufferList[j++] = (TPM2B_DIGEST *)contextV;
bufferList[j++] = (TPM2B_DIGEST *)&(tpm2bBits.b);
- bufferList[j++] = (TPM2B_DIGEST *)0;
- rval = tpm_hmac(sapi_context, hashAlg, key, (TPM2B **)&( bufferList[0] ), &tmpResult );
- if( rval != TPM_RC_SUCCESS )
- {
- return( rval );
+ bufferList[j] = (TPM2B_DIGEST *)0;
+
+ int c;
+ for(c=0; c < j; c++) {
+ TPM2B_DIGEST *digest = bufferList[c];
+ int rc = HMAC_Update(&ctx, digest->b.buffer, digest->b.size);
+ if (!rc) {
+ LOG_ERR("HMAC Update failed: %s", ERR_error_string(rc, NULL));
+ rval = TPM_RC_MEMORY;
+ goto err;
+ }
}
+ unsigned size = sizeof(tmpResult.t.buffer);
+ int rc = HMAC_Final(&ctx, tmpResult.t.buffer, &size);
+ if (!rc) {
+ LOG_ERR("HMAC Final failed: %s", ERR_error_string(rc, NULL));
+ rval = TPM_RC_MEMORY;
+ goto err;
+ }
+
+ tmpResult.t.size = size;
+
bool res = string_bytes_concat_buffer(resultKey, &(tmpResult.b));
if (!res) {
- return TSS2_SYS_RC_BAD_VALUE;
+ rval = TSS2_SYS_RC_BAD_VALUE;
+ goto err;
}
}
// Truncate the result to the desired size.
resultKey->t.size = bytes;
- return TPM_RC_SUCCESS;
+err:
+ HMAC_CTX_cleanup(&ctx);
+
+ return rval;
}
Index: tpm2.0-tools-2.0.0/lib/tpm_kdfa.h
===================================================================
--- tpm2.0-tools-2.0.0.orig/lib/tpm_kdfa.h
+++ tpm2.0-tools-2.0.0/lib/tpm_kdfa.h
@@ -42,7 +42,7 @@
* @param resultKey
* @return
*/
-TPM_RC tpm_kdfa(TSS2_SYS_CONTEXT *sapi_context, TPMI_ALG_HASH hashAlg,
+TPM_RC tpm_kdfa(TPMI_ALG_HASH hashAlg,
TPM2B *key, char *label, TPM2B *contextU, TPM2B *contextV,
UINT16 bits, TPM2B_MAX_BUFFER *resultKey );
Index: tpm2.0-tools-2.0.0/lib/tpm_session.c
===================================================================
--- tpm2.0-tools-2.0.0.orig/lib/tpm_session.c
+++ tpm2.0-tools-2.0.0/lib/tpm_session.c
@@ -198,7 +198,7 @@ static TPM_RC StartAuthSession(TSS2_SYS_
}
else
{
- rval = tpm_kdfa(sapi_context, session->authHash, &(key.b), label, &( session->nonceNewer.b ),
+ rval = tpm_kdfa(session->authHash, &(key.b), label, &( session->nonceNewer.b ),
&( session->nonceOlder.b ), bytes * 8, (TPM2B_MAX_BUFFER *)&( session->sessionKey ) );
}
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