[PATCH v5 19/20] cryptodisk: wipe out the cached keys from protectors

[Gary Lin]

An attacker may insert a malicious disk with the same crypto UUID and
trick grub2 to mount the fake root. Even though the key from the key
protector fails to unlock the fake root, it's not wiped out cleanly so
the attacker could dump the memory to retrieve the secret key. To defend
such attack, wipe out the cached key when we don't need it.

Signed-off-by: Gary Lin <glin@suse.com>
Cc: Fabian Vogt <fvogt@suse.com>
---
 grub-core/disk/cryptodisk.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/grub-core/disk/cryptodisk.c b/grub-core/disk/cryptodisk.c
index cf37a0934..f42437f4e 100644
--- a/grub-core/disk/cryptodisk.c
+++ b/grub-core/disk/cryptodisk.c
@@ -1348,7 +1348,11 @@ grub_cryptodisk_clear_key_cache (struct 
grub_cryptomount_args *cargs)
     return;
 
   for (i = 0; cargs->protectors[i]; i++)
-    grub_free (cargs->key_cache[i].key);
+    {
+      if (cargs->key_cache[i].key)
+       grub_memset (cargs->key_cache[i].key, 0, cargs->key_cache[i].key_len);
+      grub_free (cargs->key_cache[i].key);
+    }
 
   grub_free (cargs->key_cache);
 }
-- 
2.35.3