wincng: Added explicit clear memory feature to WinCNG backend
This re-introduces the original feature proposed during
the development of the WinCNG crypto backend. It still needs
to be added to libssh2 itself and probably other backends.
Memory is cleared using the function SecureZeroMemory which is
available on Windows systems, just like the WinCNG backend.
diff --git a/configure.ac b/configure.ac
index 563fb04..24f1067 100644
--- a/configure.ac
+++ b/configure.ac
@@ -97,6 +97,7 @@
use_libz=$withval,use_libz=auto)
found_crypto=none
+support_clear_memory=no
# Look for OpenSSL
if test "$found_crypto" = "none" && test "$use_openssl" != "no"; then
@@ -150,6 +151,7 @@
LIBS="$LIBS -lcrypt32"
fi
found_crypto="Windows Cryptography API: Next Generation"
+ support_clear_memory=yes
fi
AM_CONDITIONAL(WINCNG, test "$ac_cv_libbcrypt" = "yes")
@@ -197,6 +199,26 @@
AC_DEFINE(LIBSSH2_DH_GEX_NEW, 1, [Enable newer diffie-hellman-group-exchange-sha1 syntax])
fi
+AC_ARG_ENABLE(clear-memory,
+ AC_HELP_STRING([--disable-clear-memory],[Disable clearing of memory before being freed]),
+ [CLEAR_MEMORY=$enableval])
+if test "$CLEAR_MEMORY" != "no"; then
+ if test "$support_clear_memory" = "yes"; then
+ AC_DEFINE(LIBSSH2_CLEAR_MEMORY, 1, [Enable clearing of memory before being freed])
+ enable_clear_memory=yes
+ else
+ AC_MSG_ERROR([secure clearing/zeroing of memory is not supported by the selected crypto backend])
+ enable_clear_memory=unsupported
+ fi
+else
+ if test "$support_clear_memory" = "yes"; then
+ enable_clear_memory=no
+ else
+ AC_MSG_WARN([secure clearing/zeroing of memory is not supported by the selected crypto backend])
+ enable_clear_memory=unsupported
+ fi
+fi
+
dnl ************************************************************
dnl option to switch on compiler debug options
dnl
@@ -362,6 +384,7 @@
Compiler flags: ${CFLAGS}
Library types: Shared=${enable_shared}, Static=${enable_static}
Crypto library: ${found_crypto}
+ Clear memory: $enable_clear_memory
Debug build: $enable_debug
Build examples: $build_examples
Path to sshd: $ac_cv_path_SSHD (only for self-tests)
diff --git a/src/wincng.c b/src/wincng.c
index 0e165ed..ed6c6e9 100644
--- a/src/wincng.c
+++ b/src/wincng.c
@@ -285,6 +285,20 @@
return BCRYPT_SUCCESS(ret) ? 0 : -1;
}
+static void
+_libssh2_wincng_safe_free(void *buf, int len)
+{
+ if (!buf)
+ return;
+
+#ifdef LIBSSH2_CLEAR_MEMORY
+ if (len > 0)
+ SecureZeroMemory(buf, len);
+#endif
+
+ free(buf);
+}
+
/*******************************************************************/
/*
@@ -327,7 +341,7 @@
pbHashObject, dwHashObject,
key, keylen, 0);
if (!BCRYPT_SUCCESS(ret)) {
- free(pbHashObject);
+ _libssh2_wincng_safe_free(pbHashObject, dwHashObject);
return -1;
}
@@ -360,11 +374,11 @@
ret = BCryptFinishHash(ctx->hHash, hash, ctx->cbHash, 0);
BCryptDestroyHash(ctx->hHash);
+ ctx->hHash = NULL;
- if (ctx->pbHashObject)
- free(ctx->pbHashObject);
-
- memset(ctx, 0, sizeof(_libssh2_wincng_hash_ctx));
+ _libssh2_wincng_safe_free(ctx->pbHashObject, ctx->dwHashObject);
+ ctx->pbHashObject = NULL;
+ ctx->dwHashObject = 0;
return ret;
}
@@ -408,11 +422,11 @@
_libssh2_wincng_hmac_cleanup(_libssh2_wincng_hash_ctx *ctx)
{
BCryptDestroyHash(ctx->hHash);
+ ctx->hHash = NULL;
- if (ctx->pbHashObject)
- free(ctx->pbHashObject);
-
- memset(ctx, 0, sizeof(_libssh2_wincng_hash_ctx));
+ _libssh2_wincng_safe_free(ctx->pbHashObject, ctx->dwHashObject);
+ ctx->pbHashObject = NULL;
+ ctx->dwHashObject = 0;
}
@@ -454,17 +468,17 @@
_libssh2_wincng.hAlgHashSHA1,
hash, hashlen);
- free(data);
+ _libssh2_wincng_safe_free(data, datalen);
if (ret) {
- free(hash);
+ _libssh2_wincng_safe_free(hash, hashlen);
return -1;
}
datalen = sig_len;
data = malloc(datalen);
if (!data) {
- free(hash);
+ _libssh2_wincng_safe_free(hash, hashlen);
return -1;
}
@@ -479,8 +493,8 @@
ret = BCryptVerifySignature(ctx->hKey, pPaddingInfo,
hash, hashlen, data, datalen, flags);
- free(hash);
- free(data);
+ _libssh2_wincng_safe_free(hash, hashlen);
+ _libssh2_wincng_safe_free(data, datalen);
return BCRYPT_SUCCESS(ret) ? 0 : -1;
}
@@ -611,7 +625,7 @@
pbEncoded, cbEncoded, 0, NULL,
pbDecoded, &cbDecoded);
if (!ret) {
- free(pbDecoded);
+ _libssh2_wincng_safe_free(pbDecoded, cbDecoded);
return -1;
}
@@ -682,7 +696,7 @@
*ppbDecoded = pbDecoded;
*pcbDecoded = cbDecoded;
}
- free(pbInteger);
+ _libssh2_wincng_safe_free(pbInteger, cbInteger);
}
return ret;
@@ -727,10 +741,10 @@
*pcbCount = length;
} else {
for (length = 0; length < index; length++) {
- if (rpbDecoded[length]) {
- free(rpbDecoded[length]);
- rpbDecoded[length] = NULL;
- }
+ _libssh2_wincng_safe_free(rpbDecoded[length],
+ rcbDecoded[length]);
+ rpbDecoded[length] = NULL;
+ rcbDecoded[length] = 0;
}
free(rpbDecoded);
free(rcbDecoded);
@@ -743,7 +757,7 @@
ret = -1;
}
- free(pbDecoded);
+ _libssh2_wincng_safe_free(pbDecoded, cbDecoded);
}
return ret;
@@ -889,7 +903,7 @@
ret = BCryptImportKeyPair(_libssh2_wincng.hAlgRSA, NULL, lpszBlobType,
&hKey, key, keylen, 0);
if (!BCRYPT_SUCCESS(ret)) {
- free(key);
+ _libssh2_wincng_safe_free(key, keylen);
return -1;
}
@@ -897,7 +911,7 @@
*rsa = malloc(sizeof(libssh2_rsa_ctx));
if (!(*rsa)) {
BCryptDestroyKey(hKey);
- free(key);
+ _libssh2_wincng_safe_free(key, keylen);
return -1;
}
@@ -926,7 +940,7 @@
PKCS_RSA_PRIVATE_KEY,
&pbStructInfo, &cbStructInfo);
- free(pbEncoded);
+ _libssh2_wincng_safe_free(pbEncoded, cbEncoded);
if (ret) {
return -1;
@@ -937,7 +951,7 @@
LEGACY_RSAPRIVATE_BLOB, &hKey,
pbStructInfo, cbStructInfo, 0);
if (!BCRYPT_SUCCESS(ret)) {
- free(pbStructInfo);
+ _libssh2_wincng_safe_free(pbStructInfo, cbStructInfo);
return -1;
}
@@ -945,7 +959,7 @@
*rsa = malloc(sizeof(libssh2_rsa_ctx));
if (!(*rsa)) {
BCryptDestroyKey(hKey);
- free(pbStructInfo);
+ _libssh2_wincng_safe_free(pbStructInfo, cbStructInfo);
return -1;
}
@@ -1079,7 +1093,7 @@
ret = STATUS_NO_MEMORY;
}
- free(data);
+ _libssh2_wincng_safe_free(data, datalen);
return BCRYPT_SUCCESS(ret) ? 0 : -1;
}
@@ -1091,12 +1105,10 @@
return;
BCryptDestroyKey(rsa->hKey);
+ rsa->hKey = NULL;
- if (rsa->pbKeyObject)
- free(rsa->pbKeyObject);
-
- memset(rsa, 0, sizeof(libssh2_rsa_ctx));
- free(rsa);
+ _libssh2_wincng_safe_free(rsa->pbKeyObject, rsa->cbKeyObject);
+ _libssh2_wincng_safe_free(rsa, sizeof(libssh2_rsa_ctx));
}
@@ -1190,7 +1202,7 @@
ret = BCryptImportKeyPair(_libssh2_wincng.hAlgDSA, NULL, lpszBlobType,
&hKey, key, keylen, 0);
if (!BCRYPT_SUCCESS(ret)) {
- free(key);
+ _libssh2_wincng_safe_free(key, keylen);
return -1;
}
@@ -1198,7 +1210,7 @@
*dsa = malloc(sizeof(libssh2_dsa_ctx));
if (!(*dsa)) {
BCryptDestroyKey(hKey);
- free(key);
+ _libssh2_wincng_safe_free(key, keylen);
return -1;
}
@@ -1225,7 +1237,7 @@
ret = _libssh2_wincng_asn_decode_bns(pbEncoded, cbEncoded,
&rpbDecoded, &rcbDecoded, &length);
- free(pbEncoded);
+ _libssh2_wincng_safe_free(pbEncoded, cbEncoded);
if (ret) {
return -1;
@@ -1244,10 +1256,9 @@
}
for (index = 0; index < length; index++) {
- if (rpbDecoded[index]) {
- free(rpbDecoded[index]);
- rpbDecoded[index] = NULL;
- }
+ _libssh2_wincng_safe_free(rpbDecoded[index], rcbDecoded[index]);
+ rpbDecoded[index] = NULL;
+ rcbDecoded[index] = 0;
}
free(rpbDecoded);
@@ -1361,14 +1372,14 @@
memcpy(sig_fixed, sig, siglen);
}
- free(sig);
+ _libssh2_wincng_safe_free(sig, siglen);
} else
ret = STATUS_NO_MEMORY;
} else
ret = STATUS_NO_MEMORY;
}
- free(data);
+ _libssh2_wincng_safe_free(data, datalen);
return BCRYPT_SUCCESS(ret) ? 0 : -1;
}
@@ -1380,12 +1391,10 @@
return;
BCryptDestroyKey(dsa->hKey);
+ dsa->hKey = NULL;
- if (dsa->pbKeyObject)
- free(dsa->pbKeyObject);
-
- memset(dsa, 0, sizeof(libssh2_dsa_ctx));
- free(dsa);
+ _libssh2_wincng_safe_free(dsa->pbKeyObject, dsa->cbKeyObject);
+ _libssh2_wincng_safe_free(dsa, sizeof(libssh2_dsa_ctx));
}
#endif
@@ -1430,7 +1439,7 @@
ret = _libssh2_wincng_asn_decode_bns(pbEncoded, cbEncoded,
&rpbDecoded, &rcbDecoded, &length);
- free(pbEncoded);
+ _libssh2_wincng_safe_free(pbEncoded, cbEncoded);
if (ret) {
return -1;
@@ -1503,10 +1512,9 @@
for (index = 0; index < length; index++) {
- if (rpbDecoded[index]) {
- free(rpbDecoded[index]);
- rpbDecoded[index] = NULL;
- }
+ _libssh2_wincng_safe_free(rpbDecoded[index], rcbDecoded[index]);
+ rpbDecoded[index] = NULL;
+ rcbDecoded[index] = 0;
}
free(rpbDecoded);
@@ -1667,10 +1675,10 @@
ret = BCryptImportKey(*type.phAlg, NULL, BCRYPT_KEY_DATA_BLOB, &hKey,
pbKeyObject, dwKeyObject, key, keylen, 0);
- free(key);
+ _libssh2_wincng_safe_free(key, keylen);
if (!BCRYPT_SUCCESS(ret)) {
- free(pbKeyObject);
+ _libssh2_wincng_safe_free(pbKeyObject, dwKeyObject);
return -1;
}
@@ -1678,7 +1686,7 @@
pbIV = malloc(dwBlockLength);
if (!pbIV) {
BCryptDestroyKey(hKey);
- free(pbKeyObject);
+ _libssh2_wincng_safe_free(pbKeyObject, dwKeyObject);
return -1;
}
dwIV = dwBlockLength;
@@ -1737,7 +1745,7 @@
memcpy(block, pbOutput, cbOutput);
}
- free(pbOutput);
+ _libssh2_wincng_safe_free(pbOutput, cbOutput);
} else
ret = STATUS_NO_MEMORY;
}
@@ -1749,13 +1757,11 @@
_libssh2_wincng_cipher_dtor(_libssh2_cipher_ctx *ctx)
{
BCryptDestroyKey(ctx->hKey);
+ ctx->hKey = NULL;
- if (ctx->pbKeyObject) {
- free(ctx->pbKeyObject);
- ctx->pbKeyObject = NULL;
- }
-
- memset(ctx, 0, sizeof(_libssh2_cipher_ctx));
+ _libssh2_wincng_safe_free(ctx->pbKeyObject, ctx->dwKeyObject);
+ ctx->pbKeyObject = NULL;
+ ctx->dwKeyObject = 0;
}
@@ -1789,6 +1795,12 @@
if (length == bn->length)
return 0;
+#ifdef LIBSSH2_CLEAR_MEMORY
+ if (bn->bignum && bn->length > 0 && length < bn->length) {
+ SecureZeroMemory(bn->bignum + length, bn->length - length);
+ }
+#endif
+
bignum = realloc(bn->bignum, length);
if (!bignum)
return -1;
@@ -1896,7 +1908,7 @@
r->bignum, r->length, &offset,
BCRYPT_PAD_NONE);
- free(bignum);
+ _libssh2_wincng_safe_free(bignum, length);
if (BCRYPT_SUCCESS(ret)) {
_libssh2_wincng_bignum_resize(r, offset);
@@ -1910,7 +1922,7 @@
BCryptDestroyKey(hKey);
}
- free(key);
+ _libssh2_wincng_safe_free(key, keylen);
return BCRYPT_SUCCESS(ret) ? 0 : -1;
}
@@ -1988,6 +2000,10 @@
if (offset > 0) {
memmove(bn->bignum, bn->bignum + offset, length);
+#ifdef LIBSSH2_CLEAR_MEMORY
+ SecureZeroMemory(bn->bignum + length, offset);
+#endif
+
bignum = realloc(bn->bignum, length);
if (bignum) {
bn->bignum = bignum;
@@ -2009,11 +2025,11 @@
{
if (bn) {
if (bn->bignum) {
- free(bn->bignum);
+ _libssh2_wincng_safe_free(bn->bignum, bn->length);
bn->bignum = NULL;
}
bn->length = 0;
- free(bn);
+ _libssh2_wincng_safe_free(bn, sizeof(_libssh2_bn));
}
}
