From 5a690183091c2c161481123b17e1925148e516e4 Mon Sep 17 00:00:00 2001
From: Daniel Axtens <dja@axtens.net>
Date: Tue, 30 Nov 2021 15:00:57 +1100
Subject: [PATCH 23/23] x509: allow Digitial Signature plus other Key Usages

Currently the x509 certificate parser for appended signature
verification requires that the certificate have the Digitial Signature
key usage and _only_ the Digitial Signature use. This is overly strict
and becomes policy enforcement rather than a security property.

Require that the Digitial Signature usage is present, but do not
require that it is the only usage present.

Reported-by: Michal Suchanek <msuchanek@suse.com>
Signed-off-by: Daniel Axtens <dja@axtens.net>
---
 grub-core/commands/appendedsig/x509.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/grub-core/commands/appendedsig/x509.c b/grub-core/commands/appendedsig/x509.c
index 70480aa73..6ae985b30 100644
--- a/grub-core/commands/appendedsig/x509.c
+++ b/grub-core/commands/appendedsig/x509.c
@@ -547,7 +547,7 @@ cleanup:
 
 /*
  * Verify the Key Usage extension.
- * We only permit the Digital signature usage.
+ * We require the Digital signature usage.
  */
 static grub_err_t
 verify_key_usage (grub_uint8_t *value, int value_size)
@@ -586,10 +586,10 @@ verify_key_usage (grub_uint8_t *value, int value_size)
       goto cleanup;
     }
 
-  if (usage != digitalSignatureUsage)
+  if (!(usage & digitalSignatureUsage))
     {
       err =
-	grub_error (GRUB_ERR_BAD_FILE_TYPE, "Unexpected Key Usage value: %x",
+	grub_error (GRUB_ERR_BAD_FILE_TYPE, "Key Usage (0x%x) missing Digital Signature usage",
 		    usage);
       goto cleanup;
     }
-- 
2.31.1