verifiers: Add possibility to defer verification to other verifiers

This way if a verifier requires verification of a given file it can defer task
to another verifier (another authority) 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>
Reviewed-by: Ross Philipson <ross.philipson@oracle.com>

diff --git a/grub-core/commands/verifiers.c b/grub-core/commands/verifiers.c
index 59ea418a2d9741968cd1bfcc0e260f159e15bde2..c638d5f43e08545738f7cb1bebebb709828af7d1 100644 (file)
--- a/grub-core/commands/verifiers.c
+++ b/grub-core/commands/verifiers.c
@@ -83,6 +83,7 @@ grub_verifiers_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_verifiers_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_AUTH)
+       {
+         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_verifiers_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_AUTH)
        continue;
       err = ver->write (context, verified->buf, ret->size);
       if (err)

diff --git a/include/grub/verify.h b/include/grub/verify.h
index 9f892d8fedb3347955961fafaa3996e7a0993237..79022b42258243128eebc1bf55f27700a14f876c 100644 (file)
--- a/include/grub/verify.h
+++ b/include/grub/verify.h
@@ -22,7 +22,9 @@
 enum grub_verify_flags
   {
     GRUB_VERIFY_FLAGS_SKIP_VERIFICATION        = 1,
-    GRUB_VERIFY_FLAGS_SINGLE_CHUNK     = 2
+    GRUB_VERIFY_FLAGS_SINGLE_CHUNK     = 2,
+    /* Defer verification to another authority. */
+    GRUB_VERIFY_FLAGS_DEFER_AUTH       = 4
   };
 
 enum grub_verify_string_type