pem: Properly handle encrypted PEM files without DEK-Info

Since `key_size` remained zero, this caused a buffer overflow when the
derived key in `pem_decrypt()` was copied to the zero-length local
buffer.

Also fixed two potential memory leaks if hashing fails and make sure
the decryption key is wiped.

Fixes: 160f4c225d ("moved PEM parsing functionality to its own plugin")

src/libstrongswan/plugins/pem/pem_builder.c

@@ -96,6 +96,11 @@ static status_t pem_decrypt(chunk_t *blob, encryption_algorithm_t alg,
 	chunk_t key = {alloca(key_size), key_size};
 	uint8_t padding, *last_padding_pos, *first_padding_pos;
 
+	if (!key_size)
+	{
+		return FAILED;
+	}
+
 	/* build key from passphrase and IV */
 	hasher = lib->crypto->create_hasher(lib->crypto, HASH_MD5);
 	if (hasher == NULL)
@@ -108,6 +113,7 @@ static status_t pem_decrypt(chunk_t *blob, encryption_algorithm_t alg,
 	if (!hasher->get_hash(hasher, passphrase, NULL) ||
 		!hasher->get_hash(hasher, salt, hash.ptr))
 	{
+		hasher->destroy(hasher);
 		return FAILED;
 	}
 	memcpy(key.ptr, hash.ptr, hash.len);
@@ -118,6 +124,7 @@ static status_t pem_decrypt(chunk_t *blob, encryption_algorithm_t alg,
 			!hasher->get_hash(hasher, passphrase, NULL) ||
 			!hasher->get_hash(hasher, salt, hash.ptr))
 		{
+			hasher->destroy(hasher);
 			return FAILED;
 		}
 		memcpy(key.ptr + hash.len, hash.ptr, key.len - hash.len);
@@ -130,25 +137,29 @@ static status_t pem_decrypt(chunk_t *blob, encryption_algorithm_t alg,
 	{
 		DBG1(DBG_ASN, "  %N encryption algorithm not available",
 			 encryption_algorithm_names, alg);
+		memwipe(key.ptr, key.len);
 		return NOT_SUPPORTED;
 	}
 
 	if (iv.len != crypter->get_iv_size(crypter) ||
 		blob->len % crypter->get_block_size(crypter))
 	{
-		crypter->destroy(crypter);
 		DBG1(DBG_ASN, "  data size is not multiple of block size");
+		crypter->destroy(crypter);
+		memwipe(key.ptr, key.len);
 		return PARSE_ERROR;
 	}
 	if (!crypter->set_key(crypter, key) ||
 		!crypter->decrypt(crypter, *blob, iv, &decrypted))
 	{
 		crypter->destroy(crypter);
+		memwipe(key.ptr, key.len);
 		return FAILED;
 	}
 	crypter->destroy(crypter);
 	memcpy(blob->ptr, decrypted.ptr, blob->len);
 	chunk_clear(&decrypted);
+	memwipe(key.ptr, key.len);
 
 	/* determine amount of padding */
 	last_padding_pos = blob->ptr + blob->len - 1;
@@ -340,6 +351,11 @@ static status_t pem_to_bin(chunk_t *blob, bool *pgp)
 	{
 		return SUCCESS;
 	}
+	if (alg == ENCR_UNDEFINED || !key_size)
+	{
+		DBG1(DBG_ASN, "  encrypted PEM file has no valid DEK-Info");
+		return PARSE_ERROR;
+	}
 
 	enumerator = lib->credmgr->create_shared_enumerator(lib->credmgr,
 											SHARED_PRIVATE_KEY_PASS, NULL, NULL);