[PATCH v4 5/9] verifiers: Add possibility to defer verification to other verifiers

[Daniel Kiper]

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 <address@hidden>
---
v4 - suggestions/fixes:
   - s/GRUB_VERIFY_FLAGS_DEFER/GRUB_VERIFY_FLAGS_DEFER_AUTH/,
   - improve comments
     (suggested by Ross Philipson),
   - improve commit message
     (suggested by Ross Philipson).
---
 grub-core/commands/verifiers.c |   23 ++++++++++++++++++++---
 include/grub/verify.h          |    4 +++-
 2 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/grub-core/commands/verifiers.c b/grub-core/commands/verifiers.c
index 59ea418..c638d5f 100644
--- 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 9f892d8..79022b4 100644
--- 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
-- 
1.7.10.4