security/keys: properly zero out sensitive key material in big_key

commit 91080180 upstream.

Error paths forgot to zero out sensitive material, so this patch changes
some kfrees into a kzfrees.
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Eric Biggers <ebiggers3@gmail.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Kirill Marinushkin <k.marinushkin@gmail.com>
Cc: security@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

security/keys/big_key.c

@@ -194,7 +194,7 @@ int big_key_preparse(struct key_preparsed_payload *prep)
 		*path = file->f_path;
 		path_get(path);
 		fput(file);
-		kfree(data);
+		kzfree(data);
 	} else {
 		/* Just store the data in a buffer */
 		void *data = kmalloc(datalen, GFP_KERNEL);
@@ -210,9 +210,9 @@ int big_key_preparse(struct key_preparsed_payload *prep)
 err_fput:
 	fput(file);
 err_enckey:
-	kfree(enckey);
+	kzfree(enckey);
 error:
-	kfree(data);
+	kzfree(data);
 	return ret;
 }
 
@@ -226,7 +226,7 @@ void big_key_free_preparse(struct key_preparsed_payload *prep)
 
 		path_put(path);
 	}
-	kfree(prep->payload.data[big_key_data]);
+	kzfree(prep->payload.data[big_key_data]);
 }
 
 /*
@@ -258,7 +258,7 @@ void big_key_destroy(struct key *key)
 		path->mnt = NULL;
 		path->dentry = NULL;
 	}
-	kfree(key->payload.data[big_key_data]);
+	kzfree(key->payload.data[big_key_data]);
 	key->payload.data[big_key_data] = NULL;
 }
 
@@ -326,7 +326,7 @@ long big_key_read(const struct key *key, char __user *buffer, size_t buflen)
 err_fput:
 		fput(file);
 error:
-		kfree(data);
+		kzfree(data);
 	} else {
 		ret = datalen;
 		if (copy_to_user(buffer, key->payload.data[big_key_data],