If the user provides a pre-allocated buffer for the hash result,
we must use that rather than re-allocating a new buffer.

Reported-by: Dorjoy Chowdhury <dorjoychy111@gmail.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
---
 crypto/hash-gcrypt.c | 15 ++++++++++++---
 crypto/hash-glib.c   | 11 +++++++++--
 crypto/hash-gnutls.c | 16 +++++++++++++---
 crypto/hash-nettle.c | 14 +++++++++++---
 4 files changed, 45 insertions(+), 11 deletions(-)

diff --git a/crypto/hash-gcrypt.c b/crypto/hash-gcrypt.c
index ccc3cce3f8..73533a4949 100644
--- a/crypto/hash-gcrypt.c
+++ b/crypto/hash-gcrypt.c
@@ -103,16 +103,25 @@ int qcrypto_gcrypt_hash_finalize(QCryptoHash *hash,
                                  size_t *result_len,
                                  Error **errp)
 {
+    int ret;
     unsigned char *digest;
     gcry_md_hd_t *ctx = hash->opaque;
 
-    *result_len = gcry_md_get_algo_dlen(qcrypto_hash_alg_map[hash->alg]);
-    if (*result_len == 0) {
+    ret = gcry_md_get_algo_dlen(qcrypto_hash_alg_map[hash->alg]);
+    if (ret == 0) {
         error_setg(errp, "Unable to get hash length");
         return -1;
     }
 
-    *result = g_new(uint8_t, *result_len);
+    if (*result_len == 0) {
+        *result_len = ret;
+        *result = g_new(uint8_t, *result_len);
+    } else if (*result_len != ret) {
+        error_setg(errp,
+                   "Result buffer size %zu is smaller than hash %d",
+                   *result_len, ret);
+        return -1;
+    }
 
     /* Digest is freed by gcry_md_close(), copy it */
     digest = gcry_md_read(*ctx, 0);
diff --git a/crypto/hash-glib.c b/crypto/hash-glib.c
index 02a6ec1edf..809cef98ae 100644
--- a/crypto/hash-glib.c
+++ b/crypto/hash-glib.c
@@ -99,8 +99,15 @@ int qcrypto_glib_hash_finalize(QCryptoHash *hash,
         return -1;
     }
 
-    *result_len = ret;
-    *result = g_new(uint8_t, *result_len);
+    if (*result_len == 0) {
+        *result_len = ret;
+        *result = g_new(uint8_t, *result_len);
+    } else if (*result_len != ret) {
+        error_setg(errp,
+                   "Result buffer size %zu is smaller than hash %d",
+                   *result_len, ret);
+        return -1;
+    }
 
     g_checksum_get_digest(ctx, *result, result_len);
     return 0;
diff --git a/crypto/hash-gnutls.c b/crypto/hash-gnutls.c
index 34a63994c9..99fbe824ea 100644
--- a/crypto/hash-gnutls.c
+++ b/crypto/hash-gnutls.c
@@ -115,14 +115,24 @@ int qcrypto_gnutls_hash_finalize(QCryptoHash *hash,
                                  Error **errp)
 {
     gnutls_hash_hd_t *ctx = hash->opaque;
+    int ret;
 
-    *result_len = gnutls_hash_get_len(qcrypto_hash_alg_map[hash->alg]);
-    if (*result_len == 0) {
+    ret = gnutls_hash_get_len(qcrypto_hash_alg_map[hash->alg]);
+    if (ret == 0) {
         error_setg(errp, "Unable to get hash length");
         return -1;
     }
 
-    *result = g_new(uint8_t, *result_len);
+    if (*result_len == 0) {
+        *result_len = ret;
+        *result = g_new(uint8_t, *result_len);
+    } else if (*result_len != ret) {
+        error_setg(errp,
+                   "Result buffer size %zu is smaller than hash %d",
+                   *result_len, ret);
+        return -1;
+    }
+
     gnutls_hash_output(*ctx, *result);
     return 0;
 }
diff --git a/crypto/hash-nettle.c b/crypto/hash-nettle.c
index 3b847aa60e..c78624b347 100644
--- a/crypto/hash-nettle.c
+++ b/crypto/hash-nettle.c
@@ -150,9 +150,17 @@ int qcrypto_nettle_hash_finalize(QCryptoHash *hash,
                                  Error **errp)
 {
     union qcrypto_hash_ctx *ctx = hash->opaque;
-
-    *result_len = qcrypto_hash_alg_map[hash->alg].len;
-    *result = g_new(uint8_t, *result_len);
+    int ret = qcrypto_hash_alg_map[hash->alg].len;
+
+    if (*result_len == 0) {
+        *result_len = ret;
+        *result = g_new(uint8_t, *result_len);
+    } else if (*result_len != ret) {
+        error_setg(errp,
+                   "Result buffer size %zu is smaller than hash %d",
+                   *result_len, ret);
+        return -1;
+    }
 
     qcrypto_hash_alg_map[hash->alg].result(ctx, *result_len, *result);
 
-- 
2.46.0