Refactor HMAC implementations

Similarly to the cryptohash implementations, this refactors the existing
HMAC code into a single set of APIs that can be plugged with any crypto
libraries PostgreSQL is built with (only OpenSSL currently).  If there
is no such libraries, a fallback implementation is available.  Those new
APIs are designed similarly to the existing cryptohash layer, so there
is no real new design here, with the same logic around buffer bound
checks and memory handling.

HMAC has a dependency on cryptohashes, so all the cryptohash types
supported by cryptohash{_openssl}.c can be used with HMAC.  This
refactoring is an advantage mainly for SCRAM, that included its own
implementation of HMAC with SHA256 without relying on the existing
crypto libraries even if PostgreSQL was built with their support.

This code has been tested on Windows and Linux, with and without
OpenSSL, across all the versions supported on HEAD from 1.1.1 down to
1.0.1.  I have also checked that the implementations are working fine
using some sample results, a custom extension of my own, and doing
cross-checks across different major versions with SCRAM with the client
and the backend.

Author: Michael Paquier
Reviewed-by: Bruce Momjian
Discussion: https://postgr.es/m/X9m0nkEJEzIPXjeZ@paquier.xyz

1 files changed, 256 insertions, 0 deletions

diff --git a/src/common/hmac_openssl.c b/src/common/hmac_openssl.c
new file mode 100644
index 00000000000..b5e3065d1a9
--- /dev/null
+++ b/src/common/hmac_openssl.c
@@ -0,0 +1,256 @@
+/*-------------------------------------------------------------------------
+ *
+ * hmac_openssl.c
+ *	  Implementation of HMAC with OpenSSL.
+ *
+ * This should only be used if code is compiled with OpenSSL support.
+ *
+ * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *	  src/common/hmac_openssl.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#ifndef FRONTEND
+#include "postgres.h"
+#else
+#include "postgres_fe.h"
+#endif
+
+#include <openssl/hmac.h>
+
+#include "common/hmac.h"
+#include "common/md5.h"
+#include "common/sha1.h"
+#include "common/sha2.h"
+#ifndef FRONTEND
+#include "utils/memutils.h"
+#include "utils/resowner.h"
+#include "utils/resowner_private.h"
+#endif
+
+/*
+ * In backend, use an allocation in TopMemoryContext to count for resowner
+ * cleanup handling if necesary.  For versions of OpenSSL where HMAC_CTX is
+ * known, just use palloc().  In frontend, use malloc to be able to return
+ * a failure status back to the caller.
+ */
+#ifndef FRONTEND
+#ifdef HAVE_HMAC_CTX_NEW
+#define ALLOC(size) MemoryContextAlloc(TopMemoryContext, size)
+#else
+#define ALLOC(size) palloc(size)
+#endif
+#define FREE(ptr) pfree(ptr)
+#else							/* FRONTEND */
+#define ALLOC(size) malloc(size)
+#define FREE(ptr) free(ptr)
+#endif							/* FRONTEND */
+
+/*
+ * Internal structure for pg_hmac_ctx->data with this implementation.
+ */
+struct pg_hmac_ctx
+{
+	HMAC_CTX   *hmacctx;
+	pg_cryptohash_type type;
+
+#ifndef FRONTEND
+	ResourceOwner resowner;
+#endif
+};
+
+/*
+ * pg_hmac_create
+ *
+ * Allocate a hash context.  Returns NULL on failure for an OOM.  The
+ * backend issues an error, without returning.
+ */
+pg_hmac_ctx *
+pg_hmac_create(pg_cryptohash_type type)
+{
+	pg_hmac_ctx *ctx;
+
+	ctx = ALLOC(sizeof(pg_hmac_ctx));
+	if (ctx == NULL)
+		return NULL;
+	memset(ctx, 0, sizeof(pg_hmac_ctx));
+
+	ctx->type = type;
+
+	/*
+	 * Initialization takes care of assigning the correct type for OpenSSL.
+	 */
+#ifdef HAVE_HMAC_CTX_NEW
+#ifndef FRONTEND
+	ResourceOwnerEnlargeHMAC(CurrentResourceOwner);
+#endif
+	ctx->hmacctx = HMAC_CTX_new();
+#else
+	ctx->hmacctx = ALLOC(sizeof(HMAC_CTX));
+#endif
+
+	if (ctx->hmacctx == NULL)
+	{
+		explicit_bzero(ctx, sizeof(pg_hmac_ctx));
+		FREE(ctx);
+#ifndef FRONTEND
+		ereport(ERROR,
+				(errcode(ERRCODE_OUT_OF_MEMORY),
+				 errmsg("out of memory")));
+#endif
+		return NULL;
+	}
+
+#ifdef HAVE_HMAC_CTX_NEW
+#ifndef FRONTEND
+	ctx->resowner = CurrentResourceOwner;
+	ResourceOwnerRememberHMAC(CurrentResourceOwner, PointerGetDatum(ctx));
+#endif
+#else
+	memset(ctx->hmacctx, 0, sizeof(HMAC_CTX));
+#endif							/* HAVE_HMAC_CTX_NEW */
+
+	return ctx;
+}
+
+/*
+ * pg_hmac_init
+ *
+ * Initialize a HMAC context.  Returns 0 on success, -1 on failure.
+ */
+int
+pg_hmac_init(pg_hmac_ctx *ctx, const uint8 *key, size_t len)
+{
+	int			status = 0;
+
+	if (ctx == NULL)
+		return -1;
+
+	switch (ctx->type)
+	{
+		case PG_MD5:
+			status = HMAC_Init_ex(ctx->hmacctx, key, len, EVP_md5(), NULL);
+			break;
+		case PG_SHA1:
+			status = HMAC_Init_ex(ctx->hmacctx, key, len, EVP_sha1(), NULL);
+			break;
+		case PG_SHA224:
+			status = HMAC_Init_ex(ctx->hmacctx, key, len, EVP_sha224(), NULL);
+			break;
+		case PG_SHA256:
+			status = HMAC_Init_ex(ctx->hmacctx, key, len, EVP_sha256(), NULL);
+			break;
+		case PG_SHA384:
+			status = HMAC_Init_ex(ctx->hmacctx, key, len, EVP_sha384(), NULL);
+			break;
+		case PG_SHA512:
+			status = HMAC_Init_ex(ctx->hmacctx, key, len, EVP_sha512(), NULL);
+			break;
+	}
+
+	/* OpenSSL internals return 1 on success, 0 on failure */
+	if (status <= 0)
+		return -1;
+
+	return 0;
+}
+
+/*
+ * pg_hmac_update
+ *
+ * Update a HMAC context.  Returns 0 on success, -1 on failure.
+ */
+int
+pg_hmac_update(pg_hmac_ctx *ctx, const uint8 *data, size_t len)
+{
+	int			status = 0;
+
+	if (ctx == NULL)
+		return -1;
+
+	status = HMAC_Update(ctx->hmacctx, data, len);
+
+	/* OpenSSL internals return 1 on success, 0 on failure */
+	if (status <= 0)
+		return -1;
+	return 0;
+}
+
+/*
+ * pg_hmac_final
+ *
+ * Finalize a HMAC context.  Returns 0 on success, -1 on failure.
+ */
+int
+pg_hmac_final(pg_hmac_ctx *ctx, uint8 *dest, size_t len)
+{
+	int			status = 0;
+	uint32		outlen;
+
+	if (ctx == NULL)
+		return -1;
+
+	switch (ctx->type)
+	{
+		case PG_MD5:
+			if (len < MD5_DIGEST_LENGTH)
+				return -1;
+			break;
+		case PG_SHA1:
+			if (len < SHA1_DIGEST_LENGTH)
+				return -1;
+			break;
+		case PG_SHA224:
+			if (len < PG_SHA224_DIGEST_LENGTH)
+				return -1;
+			break;
+		case PG_SHA256:
+			if (len < PG_SHA256_DIGEST_LENGTH)
+				return -1;
+			break;
+		case PG_SHA384:
+			if (len < PG_SHA384_DIGEST_LENGTH)
+				return -1;
+			break;
+		case PG_SHA512:
+			if (len < PG_SHA512_DIGEST_LENGTH)
+				return -1;
+			break;
+	}
+
+	status = HMAC_Final(ctx->hmacctx, dest, &outlen);
+
+	/* OpenSSL internals return 1 on success, 0 on failure */
+	if (status <= 0)
+		return -1;
+	return 0;
+}
+
+/*
+ * pg_hmac_free
+ *
+ * Free a HMAC context.
+ */
+void
+pg_hmac_free(pg_hmac_ctx *ctx)
+{
+	if (ctx == NULL)
+		return;
+
+#ifdef HAVE_HMAC_CTX_FREE
+	HMAC_CTX_free(ctx->hmacctx);
+#ifndef FRONTEND
+	ResourceOwnerForgetHMAC(ctx->resowner, PointerGetDatum(ctx));
+#endif
+#else
+	explicit_bzero(ctx->hmacctx, sizeof(HMAC_CTX));
+	FREE(ctx->hmacctx);
+#endif
+
+	explicit_bzero(ctx, sizeof(pg_hmac_ctx));
+	FREE(ctx);
+}