From 5342b880f42bf6899eff352c83007b8f0e5fe69d Mon Sep 17 00:00:00 2001
From: Michael Marineau <michael.marineau@coreos.com>
Date: Wed, 21 Sep 2016 15:29:55 -0700
Subject: [PATCH] gpt: read entries table at the same time as the header

I personally think this reads easier. Also has the side effect of
directly comparing the primary and backup tables instead of presuming
they are equal if the crc32 matches.
---
 grub-core/lib/gpt.c | 69 +++++++++++++++++++++++++++------------------
 1 file changed, 41 insertions(+), 28 deletions(-)

diff --git a/grub-core/lib/gpt.c b/grub-core/lib/gpt.c
index abc96dee0..1910e0a86 100644
--- a/grub-core/lib/gpt.c
+++ b/grub-core/lib/gpt.c
@@ -32,6 +32,11 @@ GRUB_MOD_LICENSE ("GPLv3+");
 
 static grub_uint8_t grub_gpt_magic[] = GRUB_GPT_HEADER_MAGIC;
 
+static grub_err_t
+grub_gpt_read_entries (grub_disk_t disk, grub_gpt_t gpt,
+		       struct grub_gpt_header *header,
+		       void **ret_entries,
+		       grub_size_t *ret_entries_size);
 
 char *
 grub_gpt_guid_to_str (grub_gpt_guid_t *guid)
@@ -401,12 +406,21 @@ grub_gpt_read_primary (grub_disk_t disk, grub_gpt_t gpt)
     return grub_errno;
 
   gpt->status |= GRUB_GPT_PRIMARY_HEADER_VALID;
+
+  if (grub_gpt_read_entries (disk, gpt, &gpt->primary,
+			     &gpt->entries, &gpt->entries_size))
+    return grub_errno;
+
+  gpt->status |= GRUB_GPT_PRIMARY_ENTRIES_VALID;
+
   return GRUB_ERR_NONE;
 }
 
 static grub_err_t
 grub_gpt_read_backup (grub_disk_t disk, grub_gpt_t gpt)
 {
+  void *entries = NULL;
+  grub_size_t entries_size;
   grub_uint64_t sector;
   grub_disk_addr_t addr;
 
@@ -434,12 +448,35 @@ grub_gpt_read_backup (grub_disk_t disk, grub_gpt_t gpt)
     return grub_error (GRUB_ERR_BAD_PART_TABLE, "invalid backup GPT LBA");
 
   gpt->status |= GRUB_GPT_BACKUP_HEADER_VALID;
+
+  if (grub_gpt_read_entries (disk, gpt, &gpt->backup,
+			     &entries, &entries_size))
+    return grub_errno;
+
+  if (gpt->status & GRUB_GPT_PRIMARY_ENTRIES_VALID)
+    {
+      if (entries_size != gpt->entries_size ||
+	  grub_memcmp (entries, gpt->entries, entries_size) != 0)
+	return grub_error (GRUB_ERR_BAD_PART_TABLE, "backup GPT out of sync");
+
+      grub_free (entries);
+    }
+  else
+    {
+      gpt->entries = entries;
+      gpt->entries_size = entries_size;
+    }
+
+  gpt->status |= GRUB_GPT_BACKUP_ENTRIES_VALID;
+
   return GRUB_ERR_NONE;
 }
 
 static grub_err_t
 grub_gpt_read_entries (grub_disk_t disk, grub_gpt_t gpt,
-		       struct grub_gpt_header *header)
+		       struct grub_gpt_header *header,
+		       void **ret_entries,
+		       grub_size_t *ret_entries_size)
 {
   void *entries = NULL;
   grub_uint32_t count, size, crc;
@@ -481,9 +518,8 @@ grub_gpt_read_entries (grub_disk_t disk, grub_gpt_t gpt,
       goto fail;
     }
 
-  grub_free (gpt->entries);
-  gpt->entries = entries;
-  gpt->entries_size = entries_size;
+  *ret_entries = entries;
+  *ret_entries_size = entries_size;
   return GRUB_ERR_NONE;
 
 fail:
@@ -522,30 +558,7 @@ grub_gpt_read (grub_disk_t disk)
     grub_gpt_read_backup (disk, gpt);
 
   /* If either succeeded clear any possible error from the other.  */
-  if (gpt->status & GRUB_GPT_PRIMARY_HEADER_VALID ||
-      gpt->status & GRUB_GPT_BACKUP_HEADER_VALID)
-    grub_errno = GRUB_ERR_NONE;
-  else
-    goto fail;
-
-  /* Similarly, favor the value or error from the primary table.  */
-  if (gpt->status & GRUB_GPT_BACKUP_HEADER_VALID &&
-      !grub_gpt_read_entries (disk, gpt, &gpt->backup))
-    {
-      grub_dprintf ("gpt", "read valid backup GPT from %s\n", disk->name);
-      gpt->status |= GRUB_GPT_BACKUP_ENTRIES_VALID;
-    }
-
-  grub_errno = GRUB_ERR_NONE;
-  if (gpt->status & GRUB_GPT_PRIMARY_HEADER_VALID &&
-      !grub_gpt_read_entries (disk, gpt, &gpt->primary))
-    {
-      grub_dprintf ("gpt", "read valid primary GPT from %s\n", disk->name);
-      gpt->status |= GRUB_GPT_PRIMARY_ENTRIES_VALID;
-    }
-
-  if (gpt->status & GRUB_GPT_PRIMARY_ENTRIES_VALID ||
-      gpt->status & GRUB_GPT_BACKUP_ENTRIES_VALID)
+  if (grub_gpt_primary_valid (gpt) || grub_gpt_backup_valid (gpt))
     grub_errno = GRUB_ERR_NONE;
   else
     goto fail;