Add result size as argument of pg_cryptohash_final() for overflow checks

With its current design, a careless use of pg_cryptohash_final() could
would result in an out-of-bound write in memory as the size of the
destination buffer to store the result digest is not known to the
cryptohash internals, without the caller knowing about that.  This
commit adds a new argument to pg_cryptohash_final() to allow such sanity
checks, and implements such defenses.

The internals of SCRAM for HMAC could be tightened a bit more, but as
everything is based on SCRAM_KEY_LEN with uses particular to this code
there is no need to complicate its interface more than necessary, and
this comes back to the refactoring of HMAC in core.  Except that, this
minimizes the uses of the existing DIGEST_LENGTH variables, relying
instead on sizeof() for the result sizes.  In ossp-uuid, this also makes
the code more defensive, as it already relied on dce_uuid_t being at
least the size of a MD5 digest.

This is in philosophy similar to cfc40d38 for base64.c and aef8948f for
hex.c.

Reported-by: Ranier Vilela
Author: Michael Paquier, Ranier Vilela
Reviewed-by: Kyotaro Horiguchi
Discussion: https://postgr.es/m/CAEudQAoqEGmcff3J4sTSV-R_16Monuz-UpJFbf_dnVH=APr02Q@mail.gmail.com

contrib/pgcrypto/internal-sha2.c

@@ -118,7 +118,7 @@ int_sha2_finish(PX_MD *h, uint8 *dst)
 {
 	pg_cryptohash_ctx *ctx = (pg_cryptohash_ctx *) h->p.ptr;
 
-	if (pg_cryptohash_final(ctx, dst) < 0)
+	if (pg_cryptohash_final(ctx, dst, h->result_size(h)) < 0)
 		elog(ERROR, "could not finalize %s context", "SHA2");
 }
 

contrib/pgcrypto/internal.c

@@ -106,7 +106,7 @@ int_md5_finish(PX_MD *h, uint8 *dst)
 {
 	pg_cryptohash_ctx *ctx = (pg_cryptohash_ctx *) h->p.ptr;
 
-	if (pg_cryptohash_final(ctx, dst) < 0)
+	if (pg_cryptohash_final(ctx, dst, h->result_size(h)) < 0)
 		elog(ERROR, "could not finalize %s context", "MD5");
 }
 
@@ -156,7 +156,7 @@ int_sha1_finish(PX_MD *h, uint8 *dst)
 {
 	pg_cryptohash_ctx *ctx = (pg_cryptohash_ctx *) h->p.ptr;
 
-	if (pg_cryptohash_final(ctx, dst) < 0)
+	if (pg_cryptohash_final(ctx, dst, h->result_size(h)) < 0)
 		elog(ERROR, "could not finalize %s context", "SHA1");
 }
 

contrib/uuid-ossp/uuid-ossp.c

@@ -324,7 +324,8 @@ uuid_generate_internal(int v, unsigned char *ns, const char *ptr, int len)
 						pg_cryptohash_update(ctx, (unsigned char *) ptr, len) < 0)
 						elog(ERROR, "could not update %s context", "MD5");
 					/* we assume sizeof MD5 result is 16, same as UUID size */
-					if (pg_cryptohash_final(ctx, (unsigned char *) &uu) < 0)
+					if (pg_cryptohash_final(ctx, (unsigned char *) &uu,
+											sizeof(uu)) < 0)
 						elog(ERROR, "could not finalize %s context", "MD5");
 					pg_cryptohash_free(ctx);
 				}
@@ -338,7 +339,7 @@ uuid_generate_internal(int v, unsigned char *ns, const char *ptr, int len)
 					if (pg_cryptohash_update(ctx, ns, sizeof(uu)) < 0 ||
 						pg_cryptohash_update(ctx, (unsigned char *) ptr, len) < 0)
 						elog(ERROR, "could not update %s context", "SHA1");
-					if (pg_cryptohash_final(ctx, sha1result) < 0)
+					if (pg_cryptohash_final(ctx, sha1result, sizeof(sha1result)) < 0)
 						elog(ERROR, "could not finalize %s context", "SHA1");
 					pg_cryptohash_free(ctx);
 

src/backend/libpq/auth-scram.c

@@ -1429,7 +1429,7 @@ scram_mock_salt(const char *username)
 	if (pg_cryptohash_init(ctx) < 0 ||
 		pg_cryptohash_update(ctx, (uint8 *) username, strlen(username)) < 0 ||
 		pg_cryptohash_update(ctx, (uint8 *) mock_auth_nonce, MOCK_AUTH_NONCE_LEN) < 0 ||
-		pg_cryptohash_final(ctx, sha_digest) < 0)
+		pg_cryptohash_final(ctx, sha_digest, sizeof(sha_digest)) < 0)
 	{
 		pg_cryptohash_free(ctx);
 		return NULL;

src/backend/replication/backup_manifest.c

@@ -330,12 +330,13 @@ SendBackupManifest(backup_manifest_info *manifest)
 	 * twice.
 	 */
 	manifest->still_checksumming = false;
-	if (pg_cryptohash_final(manifest->manifest_ctx, checksumbuf) < 0)
+	if (pg_cryptohash_final(manifest->manifest_ctx, checksumbuf,
+							sizeof(checksumbuf)) < 0)
 		elog(ERROR, "failed to finalize checksum of backup manifest");
 	AppendStringToManifest(manifest, "\"Manifest-Checksum\": \"");
-	dstlen = pg_hex_enc_len(PG_SHA256_DIGEST_LENGTH);
+	dstlen = pg_hex_enc_len(sizeof(checksumbuf));
 	checksumstringbuf = palloc0(dstlen + 1);	/* includes \0 */
-	pg_hex_encode((char *) checksumbuf, sizeof checksumbuf,
+	pg_hex_encode((char *) checksumbuf, sizeof(checksumbuf),
 				  checksumstringbuf, dstlen);
 	checksumstringbuf[dstlen] = '\0';
 	AppendStringToManifest(manifest, checksumstringbuf);

src/backend/utils/adt/cryptohashfuncs.c

@@ -114,7 +114,8 @@ cryptohash_internal(pg_cryptohash_type type, bytea *input)
 		elog(ERROR, "could not initialize %s context", typestr);
 	if (pg_cryptohash_update(ctx, data, len) < 0)
 		elog(ERROR, "could not update %s context", typestr);
-	if (pg_cryptohash_final(ctx, (unsigned char *) VARDATA(result)) < 0)
+	if (pg_cryptohash_final(ctx, (unsigned char *) VARDATA(result),
+							digest_len) < 0)
 		elog(ERROR, "could not finalize %s context", typestr);
 	pg_cryptohash_free(ctx);
 

src/bin/pg_verifybackup/parse_manifest.c

@@ -659,7 +659,8 @@ verify_manifest_checksum(JsonManifestParseState *parse, char *buffer,
 		context->error_cb(context, "could not initialize checksum of manifest");
 	if (pg_cryptohash_update(manifest_ctx, (uint8 *) buffer, penultimate_newline + 1) < 0)
 		context->error_cb(context, "could not update checksum of manifest");
-	if (pg_cryptohash_final(manifest_ctx, manifest_checksum_actual) < 0)
+	if (pg_cryptohash_final(manifest_ctx, manifest_checksum_actual,
+							sizeof(manifest_checksum_actual)) < 0)
 		context->error_cb(context, "could not finalize checksum of manifest");
 
 	/* Now verify it. */

src/common/checksum_helper.c

@@ -198,28 +198,32 @@ pg_checksum_final(pg_checksum_context *context, uint8 *output)
 			memcpy(output, &context->raw_context.c_crc32c, retval);
 			break;
 		case CHECKSUM_TYPE_SHA224:
-			if (pg_cryptohash_final(context->raw_context.c_sha2, output) < 0)
+			retval = PG_SHA224_DIGEST_LENGTH;
+			if (pg_cryptohash_final(context->raw_context.c_sha2,
+									output, retval) < 0)
 				return -1;
 			pg_cryptohash_free(context->raw_context.c_sha2);
-			retval = PG_SHA224_DIGEST_LENGTH;
 			break;
 		case CHECKSUM_TYPE_SHA256:
-			if (pg_cryptohash_final(context->raw_context.c_sha2, output) < 0)
+			retval = PG_SHA256_DIGEST_LENGTH;
+			if (pg_cryptohash_final(context->raw_context.c_sha2,
+									output, retval) < 0)
 				return -1;
 			pg_cryptohash_free(context->raw_context.c_sha2);
-			retval = PG_SHA256_DIGEST_LENGTH;
 			break;
 		case CHECKSUM_TYPE_SHA384:
-			if (pg_cryptohash_final(context->raw_context.c_sha2, output) < 0)
+			retval = PG_SHA384_DIGEST_LENGTH;
+			if (pg_cryptohash_final(context->raw_context.c_sha2,
+									output, retval) < 0)
 				return -1;
 			pg_cryptohash_free(context->raw_context.c_sha2);
-			retval = PG_SHA384_DIGEST_LENGTH;
 			break;
 		case CHECKSUM_TYPE_SHA512:
-			if (pg_cryptohash_final(context->raw_context.c_sha2, output) < 0)
+			retval = PG_SHA512_DIGEST_LENGTH;
+			if (pg_cryptohash_final(context->raw_context.c_sha2,
+									output, retval) < 0)
 				return -1;
 			pg_cryptohash_free(context->raw_context.c_sha2);
-			retval = PG_SHA512_DIGEST_LENGTH;
 			break;
 	}
 

src/common/cryptohash.c

@@ -160,12 +160,12 @@ pg_cryptohash_update(pg_cryptohash_ctx *ctx, const uint8 *data, size_t len)
 /*
  * pg_cryptohash_final
  *
- * Finalize a hash context.  Note that this implementation is designed
- * to never fail, so this always returns 0 except if the caller has
- * given a NULL context.
+ * Finalize a hash context.  Note that this implementation is designed to
+ * never fail, so this always returns 0 except if the destination buffer
+ * is not large enough.
  */
 int
-pg_cryptohash_final(pg_cryptohash_ctx *ctx, uint8 *dest)
+pg_cryptohash_final(pg_cryptohash_ctx *ctx, uint8 *dest, size_t len)
 {
 	if (ctx == NULL)
 		return -1;
@@ -173,21 +173,33 @@ pg_cryptohash_final(pg_cryptohash_ctx *ctx, uint8 *dest)
 	switch (ctx->type)
 	{
 		case PG_MD5:
+			if (len < MD5_DIGEST_LENGTH)
+				return -1;
 			pg_md5_final(&ctx->data.md5, dest);
 			break;
 		case PG_SHA1:
+			if (len < SHA1_DIGEST_LENGTH)
+				return -1;
 			pg_sha1_final(&ctx->data.sha1, dest);
 			break;
 		case PG_SHA224:
+			if (len < PG_SHA224_DIGEST_LENGTH)
+				return -1;
 			pg_sha224_final(&ctx->data.sha224, dest);
 			break;
 		case PG_SHA256:
+			if (len < PG_SHA256_DIGEST_LENGTH)
+				return -1;
 			pg_sha256_final(&ctx->data.sha256, dest);
 			break;
 		case PG_SHA384:
+			if (len < PG_SHA384_DIGEST_LENGTH)
+				return -1;
 			pg_sha384_final(&ctx->data.sha384, dest);
 			break;
 		case PG_SHA512:
+			if (len < PG_SHA512_DIGEST_LENGTH)
+				return -1;
 			pg_sha512_final(&ctx->data.sha512, dest);
 			break;
 	}

src/common/cryptohash_openssl.c

@@ -24,6 +24,9 @@
 #include <openssl/evp.h>
 
 #include "common/cryptohash.h"
+#include "common/md5.h"
+#include "common/sha1.h"
+#include "common/sha2.h"
 #ifndef FRONTEND
 #include "utils/memutils.h"
 #include "utils/resowner.h"
@@ -181,13 +184,41 @@ pg_cryptohash_update(pg_cryptohash_ctx *ctx, const uint8 *data, size_t len)
  * Finalize a hash context.  Returns 0 on success, and -1 on failure.
  */
 int
-pg_cryptohash_final(pg_cryptohash_ctx *ctx, uint8 *dest)
+pg_cryptohash_final(pg_cryptohash_ctx *ctx, uint8 *dest, size_t len)
 {
 	int			status = 0;
 
 	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 = EVP_DigestFinal_ex(ctx->evpctx, dest, 0);
 
 	/* OpenSSL internals return 1 on success, 0 on failure */

src/common/md5_common.c

@@ -78,7 +78,7 @@ pg_md5_hash(const void *buff, size_t len, char *hexsum)
 
 	if (pg_cryptohash_init(ctx) < 0 ||
 		pg_cryptohash_update(ctx, buff, len) < 0 ||
-		pg_cryptohash_final(ctx, sum) < 0)
+		pg_cryptohash_final(ctx, sum, sizeof(sum)) < 0)
 	{
 		pg_cryptohash_free(ctx);
 		return false;
@@ -100,7 +100,7 @@ pg_md5_binary(const void *buff, size_t len, void *outbuf)
 
 	if (pg_cryptohash_init(ctx) < 0 ||
 		pg_cryptohash_update(ctx, buff, len) < 0 ||
-		pg_cryptohash_final(ctx, outbuf) < 0)
+		pg_cryptohash_final(ctx, outbuf, MD5_DIGEST_LENGTH) < 0)
 	{
 		pg_cryptohash_free(ctx);
 		return false;

src/common/scram-common.c

@@ -51,7 +51,7 @@ scram_HMAC_init(scram_HMAC_ctx *ctx, const uint8 *key, int keylen)
 			return -1;
 		if (pg_cryptohash_init(sha256_ctx) < 0 ||
 			pg_cryptohash_update(sha256_ctx, key, keylen) < 0 ||
-			pg_cryptohash_final(sha256_ctx, keybuf) < 0)
+			pg_cryptohash_final(sha256_ctx, keybuf, sizeof(keybuf)) < 0)
 		{
 			pg_cryptohash_free(sha256_ctx);
 			return -1;
@@ -112,7 +112,7 @@ scram_HMAC_final(uint8 *result, scram_HMAC_ctx *ctx)
 
 	Assert(ctx->sha256ctx != NULL);
 
-	if (pg_cryptohash_final(ctx->sha256ctx, h) < 0)
+	if (pg_cryptohash_final(ctx->sha256ctx, h, sizeof(h)) < 0)
 	{
 		pg_cryptohash_free(ctx->sha256ctx);
 		return -1;
@@ -122,7 +122,7 @@ scram_HMAC_final(uint8 *result, scram_HMAC_ctx *ctx)
 	if (pg_cryptohash_init(ctx->sha256ctx) < 0 ||
 		pg_cryptohash_update(ctx->sha256ctx, ctx->k_opad, SHA256_HMAC_B) < 0 ||
 		pg_cryptohash_update(ctx->sha256ctx, h, SCRAM_KEY_LEN) < 0 ||
-		pg_cryptohash_final(ctx->sha256ctx, result) < 0)
+		pg_cryptohash_final(ctx->sha256ctx, result, SCRAM_KEY_LEN) < 0)
 	{
 		pg_cryptohash_free(ctx->sha256ctx);
 		return -1;
@@ -202,7 +202,7 @@ scram_H(const uint8 *input, int len, uint8 *result)
 
 	if (pg_cryptohash_init(ctx) < 0 ||
 		pg_cryptohash_update(ctx, input, len) < 0 ||
-		pg_cryptohash_final(ctx, result) < 0)
+		pg_cryptohash_final(ctx, result, SCRAM_KEY_LEN) < 0)
 	{
 		pg_cryptohash_free(ctx);
 		return -1;

src/include/common/cryptohash.h

@@ -32,7 +32,7 @@ typedef struct pg_cryptohash_ctx pg_cryptohash_ctx;
 extern pg_cryptohash_ctx *pg_cryptohash_create(pg_cryptohash_type type);
 extern int	pg_cryptohash_init(pg_cryptohash_ctx *ctx);
 extern int	pg_cryptohash_update(pg_cryptohash_ctx *ctx, const uint8 *data, size_t len);
-extern int	pg_cryptohash_final(pg_cryptohash_ctx *ctx, uint8 *dest);
+extern int	pg_cryptohash_final(pg_cryptohash_ctx *ctx, uint8 *dest, size_t len);
 extern void pg_cryptohash_free(pg_cryptohash_ctx *ctx);
 
 #endif							/* PG_CRYPTOHASH_H */