Revert "Change SHA2 implementation based on OpenSSL to use EVP digest routines"

This reverts commit e21cbb4b, as the switch to EVP routines requires a
more careful design where we would need to have at least our wrapper
routines return a status instead of issuing an error by themselves to
let the caller do the error handling.  The memory handling was also
incorrect and could cause leaks in the backend if a failure happened,
requiring most likely a callback to do the necessary cleanup as the only
clean way to be able to allocate an EVP context requires the use of an
allocation within OpenSSL.  The potential rework of the wrappers also
impacts the fallback implementation when not building with OpenSSL.

Originally, prairiedog has reported a compilation failure, but after
discussion with Tom Lane this needs a better design.

Discussion: https://postgr.es/m/20200928073330.GC2316@paquier.xyz

src/common/sha2_openssl.c

@@ -20,118 +20,83 @@
 #include "postgres_fe.h"
 #endif
 
-#include "common/sha2.h"
-
-#ifdef FRONTEND
-#include "common/logging.h"
-#else
-#include "miscadmin.h"
-#endif
+#include <openssl/sha.h>
 
-#ifdef FRONTEND
-#define sha2_log_and_abort(...) \
-	do { pg_log_fatal(__VA_ARGS__); exit(1); } while(0)
-#else
-#define sha2_log_and_abort(...) elog(ERROR, __VA_ARGS__)
-#endif
-
-static void
-digest_init(EVP_MD_CTX **ctx, const EVP_MD *type)
-{
-	*ctx = EVP_MD_CTX_create();
-	if (*ctx == NULL)
-		sha2_log_and_abort("could not create EVP digest context");
-	if (EVP_DigestInit_ex(*ctx, type, NULL) <= 0)
-		sha2_log_and_abort("could not initialize EVP digest context");
-}
-
-static void
-digest_update(EVP_MD_CTX **ctx, const uint8 *data, size_t len)
-{
-	if (EVP_DigestUpdate(*ctx, data, len) <= 0)
-		sha2_log_and_abort("could not update EVP digest context");
-}
+#include "common/sha2.h"
 
-static void
-digest_final(EVP_MD_CTX **ctx, uint8 *dest)
-{
-	if (EVP_DigestFinal_ex(*ctx, dest, 0) <= 0)
-		sha2_log_and_abort("could not finalize EVP digest context");
-	EVP_MD_CTX_destroy(*ctx);
-}
 
 /* Interface routines for SHA-256 */
 void
 pg_sha256_init(pg_sha256_ctx *ctx)
 {
-	digest_init(ctx, EVP_sha256());
+	SHA256_Init((SHA256_CTX *) ctx);
 }
 
 void
 pg_sha256_update(pg_sha256_ctx *ctx, const uint8 *data, size_t len)
 {
-	digest_update(ctx, data, len);
+	SHA256_Update((SHA256_CTX *) ctx, data, len);
 }
 
 void
 pg_sha256_final(pg_sha256_ctx *ctx, uint8 *dest)
 {
-	digest_final(ctx, dest);
+	SHA256_Final(dest, (SHA256_CTX *) ctx);
 }
 
 /* Interface routines for SHA-512 */
 void
 pg_sha512_init(pg_sha512_ctx *ctx)
 {
-	digest_init(ctx, EVP_sha512());
+	SHA512_Init((SHA512_CTX *) ctx);
 }
 
 void
 pg_sha512_update(pg_sha512_ctx *ctx, const uint8 *data, size_t len)
 {
-	digest_update(ctx, data, len);
+	SHA512_Update((SHA512_CTX *) ctx, data, len);
 }
 
 void
 pg_sha512_final(pg_sha512_ctx *ctx, uint8 *dest)
 {
-	digest_final(ctx, dest);
+	SHA512_Final(dest, (SHA512_CTX *) ctx);
 }
 
 /* Interface routines for SHA-384 */
 void
 pg_sha384_init(pg_sha384_ctx *ctx)
 {
-	digest_init(ctx, EVP_sha384());
+	SHA384_Init((SHA512_CTX *) ctx);
 }
 
 void
 pg_sha384_update(pg_sha384_ctx *ctx, const uint8 *data, size_t len)
 {
-	digest_update(ctx, data, len);
+	SHA384_Update((SHA512_CTX *) ctx, data, len);
 }
 
 void
 pg_sha384_final(pg_sha384_ctx *ctx, uint8 *dest)
 {
-	digest_final(ctx, dest);
+	SHA384_Final(dest, (SHA512_CTX *) ctx);
 }
 
 /* Interface routines for SHA-224 */
 void
 pg_sha224_init(pg_sha224_ctx *ctx)
 {
-	digest_init(ctx, EVP_sha224());
+	SHA224_Init((SHA256_CTX *) ctx);
 }
 
 void
 pg_sha224_update(pg_sha224_ctx *ctx, const uint8 *data, size_t len)
 {
-	digest_update(ctx, data, len);
+	SHA224_Update((SHA256_CTX *) ctx, data, len);
 }
 
 void
 pg_sha224_final(pg_sha224_ctx *ctx, uint8 *dest)
 {
-	digest_final(ctx, dest);
+	SHA224_Final(dest, (SHA256_CTX *) ctx);
 }

src/include/common/sha2.h

@@ -51,7 +51,7 @@
 #define _PG_SHA2_H_
 
 #ifdef USE_OPENSSL
-#include <openssl/evp.h>
+#include <openssl/sha.h>
 #endif
 
 /*** SHA224/256/384/512 Various Length Definitions ***********************/
@@ -70,10 +70,10 @@
 
 /* Context Structures for SHA224/256/384/512 */
 #ifdef USE_OPENSSL
-typedef EVP_MD_CTX *pg_sha256_ctx;
-typedef EVP_MD_CTX *pg_sha512_ctx;
-typedef EVP_MD_CTX *pg_sha224_ctx;
-typedef EVP_MD_CTX *pg_sha384_ctx;
+typedef SHA256_CTX pg_sha256_ctx;
+typedef SHA512_CTX pg_sha512_ctx;
+typedef SHA256_CTX pg_sha224_ctx;
+typedef SHA512_CTX pg_sha384_ctx;
 #else
 typedef struct pg_sha256_ctx
 {