[libsecret/wip/dueno/memcmp] secret-file-collection: Make MAC comparison constant time
- From: Daiki Ueno <dueno src gnome org>
- To: commits-list gnome org
- Cc:
- Subject: [libsecret/wip/dueno/memcmp] secret-file-collection: Make MAC comparison constant time
- Date: Sun, 4 Oct 2020 15:27:54 +0000 (UTC)
commit 2f0df810846a9c16358fdac499a5bf394ec48eab
Author: Daiki Ueno <dueno src gnome org>
Date: Sun Oct 4 17:09:22 2020 +0200
secret-file-collection: Make MAC comparison constant time
libsecret/secret-file-collection.c | 43 +++++++++++++++++++++-----------------
1 file changed, 24 insertions(+), 19 deletions(-)
---
diff --git a/libsecret/secret-file-collection.c b/libsecret/secret-file-collection.c
index a27cf04..62847b9 100644
--- a/libsecret/secret-file-collection.c
+++ b/libsecret/secret-file-collection.c
@@ -130,6 +130,26 @@ do_calculate_mac (SecretFileCollection *self,
return ret;
}
+static gboolean
+do_verify_mac (SecretFileCollection *self,
+ const guint8 *value, gsize n_value,
+ const guint8 *data)
+{
+ guint8 buffer[MAC_SIZE];
+ guint8 status = 0;
+ gsize i;
+
+ if (!do_calculate_mac (self, value, n_value, buffer)) {
+ return FALSE;
+ }
+
+ for (i = 0; i < MAC_SIZE; i++) {
+ status |= data[i] ^ buffer[i];
+ }
+
+ return status == 0;
+}
+
static gboolean
do_decrypt (SecretFileCollection *self,
guint8 *data,
@@ -479,7 +499,6 @@ hashed_attributes_match (SecretFileCollection *self,
GVariant *hashed_attribute = NULL;
gpointer key;
gpointer value;
- guint8 buffer[MAC_SIZE];
g_hash_table_iter_init (&iter, attributes);
while (g_hash_table_iter_next (&iter, &key, &value)) {
@@ -497,12 +516,7 @@ hashed_attributes_match (SecretFileCollection *self,
return FALSE;
}
- if (!do_calculate_mac (self, value, strlen ((char *)value), buffer)) {
- g_variant_unref (hashed_attribute);
- return FALSE;
- }
-
- if (memcmp (data, buffer, MAC_SIZE) != 0) {
+ if (!do_verify_mac (self, value, strlen ((char *)value), data)) {
g_variant_unref (hashed_attribute);
return FALSE;
}
@@ -673,7 +687,6 @@ _secret_file_item_decrypt (GVariant *encrypted,
guint8 *data;
SecretFileItem *item;
GVariant *serialized_item;
- guint8 mac[MAC_SIZE];
g_variant_get (encrypted, "(a{say}@ay)", NULL, &blob);
@@ -691,9 +704,9 @@ _secret_file_item_decrypt (GVariant *encrypted,
"couldn't calculate mac");
return FALSE;
}
- n_padded -= IV_SIZE + MAC_SIZE;
- if (!do_calculate_mac (collection, data, n_padded + IV_SIZE, mac)) {
+ n_padded -= MAC_SIZE;
+ if (!do_verify_mac (collection, data, n_padded, data + n_padded)) {
egg_secure_free (data);
g_set_error (error,
SECRET_ERROR,
@@ -702,15 +715,7 @@ _secret_file_item_decrypt (GVariant *encrypted,
return FALSE;
}
- if (memcmp (data + n_padded + IV_SIZE, mac, MAC_SIZE) != 0) {
- egg_secure_free (data);
- g_set_error (error,
- SECRET_ERROR,
- SECRET_ERROR_PROTOCOL,
- "mac doesn't match");
- return FALSE;
- }
-
+ n_padded -= IV_SIZE;
if (!do_decrypt (collection, data, n_padded)) {
egg_secure_free (data);
g_set_error (error,
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