[PATCH v3 4/8] verifiers: Add possibility to defer verification to other verifiers

[Daniel Kiper <daniel.kiper@oracle.com>]

This way if a verifier requires verification of a given file it can
defer task to other verifier if it is not able to do it itself. E.g.
shim_lock verifier, posted as a subsequent patch, is able to verify
only PE files. This means that it is not able to verify any of GRUB2
modules which have to be trusted on UEFI systems with secure boot
enabled. So, it can defer verification to other verifier, e.g. PGP one.

I silently assume that other verifiers are trusted and will do good
job for us. Or at least they will not do any harm.

Signed-off-by: Daniel Kiper <daniel.kiper@oracle.com>
---
 grub-core/commands/verify_helper.c |   23 ++++++++++++++++++++---
 include/grub/verify.h              |    3 ++-
 2 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/grub-core/commands/verify_helper.c b/grub-core/commands/verify_helper.c
index 7effc5f..ba8b03d 100644
--- a/grub-core/commands/verify_helper.c
+++ b/grub-core/commands/verify_helper.c
@@ -83,6 +83,7 @@ grub_verify_helper_open (grub_file_t io, enum grub_file_type type)
   void *context;
   grub_file_t ret = 0;
   grub_err_t err;
+  int defer = 0;
 
   grub_dprintf ("verify", "file: %s type: %d\n", io->name, type);
 
@@ -102,13 +103,27 @@ grub_verify_helper_open (grub_file_t io, enum grub_file_type type)
       err = ver->init (io, type, &context, &flags);
       if (err)
 	goto fail_noclose;
+      if (flags & GRUB_VERIFY_FLAGS_DEFER)
+	{
+	  defer = 1;
+	  continue;
+	}
       if (!(flags & GRUB_VERIFY_FLAGS_SKIP_VERIFICATION))
 	break;
     }
 
   if (!ver)
-    /* No verifiers wanted to verify. Just return underlying file.  */
-    return io;
+    {
+      if (defer)
+	{
+	  grub_error (GRUB_ERR_ACCESS_DENIED,
+		      N_("verification requested but nobody cares: %s"), io->name);
+	  goto fail_noclose;
+	}
+
+      /* No verifiers wanted to verify. Just return underlying file. */
+      return io;
+    }
 
   ret = grub_malloc (sizeof (*ret));
   if (!ret)
@@ -160,7 +175,9 @@ grub_verify_helper_open (grub_file_t io, enum grub_file_type type)
       err = ver->init (io, type, &context, &flags);
       if (err)
 	goto fail_noclose;
-      if (flags & GRUB_VERIFY_FLAGS_SKIP_VERIFICATION)
+      if (flags & GRUB_VERIFY_FLAGS_SKIP_VERIFICATION ||
+	  /* Verification done earlier. So, we are happy here. */
+	  flags & GRUB_VERIFY_FLAGS_DEFER)
 	continue;
       err = ver->write (context, verified->buf, ret->size);
       if (err)
diff --git a/include/grub/verify.h b/include/grub/verify.h
index 9f892d8..c385e3d 100644
--- a/include/grub/verify.h
+++ b/include/grub/verify.h
@@ -22,7 +22,8 @@
 enum grub_verify_flags
   {
     GRUB_VERIFY_FLAGS_SKIP_VERIFICATION	= 1,
-    GRUB_VERIFY_FLAGS_SINGLE_CHUNK	= 2
+    GRUB_VERIFY_FLAGS_SINGLE_CHUNK	= 2,
+    GRUB_VERIFY_FLAGS_DEFER		= 4
   };
 
 enum grub_verify_string_type
-- 
1.7.10.4