partitions/efi: check pmbr record's starting lba

Per the UEFI Specs 2.4, June 2013, the starting lba of the partition that
has the EFI GPT (0xEE) must be set to 0x00000001 - this is obviously the
LBA of the GPT Partition Header.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Davidlohr Bueso <davidlohr@hp.com>
Reviewed-by: Karel Zak <kzak@redhat.com>
Acked-by: Matt Fleming <matt.fleming@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

block/partitions/efi.c

@@ -151,9 +151,18 @@ static u64 last_lba(struct block_device *bdev)
 
 static inline int pmbr_part_valid(gpt_mbr_record *part)
 {
-	if (part->os_type == EFI_PMBR_OSTYPE_EFI_GPT &&
-	    le32_to_cpu(part->start_sector) == 1UL)
+	if (part->os_type != EFI_PMBR_OSTYPE_EFI_GPT)
+		goto invalid;
+
+	/* set to 0x00000001 (i.e., the LBA of the GPT Partition Header) */
+	if (le32_to_cpu(part->starting_lba) != GPT_PRIMARY_PARTITION_TABLE_LBA)
+		goto invalid;
+
+	if (le32_to_cpu(part->start_sector) != 1UL)
+		goto invalid;
+
 	return 1;
+invalid:
 	return 0;
 }