commit 399317ede45340eebc035ba204b6201b6d62dd66
author Paul Lawrence <paullawrence@google.com> Mon Mar 10 13:20:50 2014 -0700
committer Paul Lawrence <paullawrence@google.com> Fri Mar 21 11:15:39 2014 -0700
tree 94a1ad57be778aaa5fafa5b6f60405cf29327f33
parent f8e9569507a641ece6713cb4be072d1d9cfd2dcd

Store password in vold

If we are not to double prompt, we need to pass the password from
CryptKeeper to KeyStore. Since the entire framework is taken down
and restarted, we must store the password in a secure system daemon.
There seems no better way than holding it in vold.

Change-Id: Ia60f2f051fc3f87c4b6468465f17b655f43f97de

cryptfs.c

diff --git a/cryptfs.c b/cryptfs.c
index f8d14cf..e472800 100644
--- a/cryptfs.c
+++ b/cryptfs.c
@@ -79,11 +79,23 @@
 static int  master_key_saved = 0;
 static struct crypt_persist_data *persist_data = NULL;
 
-/* Set when userdata is successfully decrypted and mounted.
- * Reset whenever read (via cryptfs_just_decrypted)
- * (Read by keyguard to avoid a double prompt.)
+/* Store password when userdata is successfully decrypted and mounted.
+ * Cleared by cryptfs_clear_password
+ *
+ * To avoid a double prompt at boot, we need to store the CryptKeeper
+ * password and pass it to KeyGuard, which uses it to unlock KeyStore.
+ * Since the entire framework is torn down and rebuilt after encryption,
+ * we have to use a daemon or similar to store the password. Since vold
+ * is secured against IPC except from system processes, it seems a reasonable
+ * place to store this.
+ *
+ * password should be cleared once it has been used.
+ *
+ * password is aged out after password_max_age_seconds seconds.
  */
-static int just_decrypted = 0;
+static char* password = 0;
+static int password_expiry_time = 0;
+static const int password_max_age_seconds = 60;
 
 extern struct fstab *fstab;
 
@@ -1472,7 +1484,11 @@
                                  DATA_MNT_POINT, "userdata");
 
     if (rc == 0 && crypt_ftr.crypt_type != CRYPT_TYPE_DEFAULT) {
-        just_decrypted = 1;
+        cryptfs_clear_password();
+        password = strdup(passwd);
+        struct timespec now;
+        clock_gettime(CLOCK_BOOTTIME, &now);
+        password_expiry_time = now.tv_sec + password_max_age_seconds;
     }
 
     return rc;
@@ -2493,9 +2509,25 @@
     return crypt_ftr.crypt_type;
 }
 
-int cryptfs_just_decrypted(void)
+char* cryptfs_get_password()
 {
-    int rc = just_decrypted;
-    just_decrypted = 0;
-    return rc;
+    struct timespec now;
+    clock_gettime(CLOCK_MONOTONIC, &now);
+    if (now.tv_sec < password_expiry_time) {
+        return password;
+    } else {
+        cryptfs_clear_password();
+        return 0;
+    }
+}
+
+void cryptfs_clear_password()
+{
+    if (password) {
+        size_t len = strlen(password);
+        memset(password, 0, len);
+        free(password);
+        password = 0;
+        password_expiry_time = 0;
+    }
 }