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 cfc40d3 for base64.c and aef8948 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

1 files changed, 16 insertions, 4 deletions

diff --git a/src/common/cryptohash.c b/src/common/cryptohash.c
index 5b2c050d799..0dab74a094b 100644
--- a/src/common/cryptohash.c
+++ b/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;
 	}