[PATCH] Ensure that the GPT header is at least the size of the structure.

[Peter Jones <pjones@redhat.com>]

UEFI 2.3.1D will include a change to the spec language mandating that a
GPT header must be greater than *or equal to* the size of the defined
structure.  While verifying that this would work on Linux, I discovered
that we're not actually checking the minimum bound at all.

The result of this is that when we verify the checksum, it's possible
that on a malformed header (with header_size of 0), we won't actually
verify any data.

Signed-off-by: Peter Jones <pjones@redhat.com>
---
 block/partitions/efi.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/block/partitions/efi.c b/block/partitions/efi.c
index b62fb88..5ad168c 100644
--- a/block/partitions/efi.c
+++ b/block/partitions/efi.c
@@ -310,15 +310,23 @@ static int is_gpt_valid(struct parsed_partitions *state, u64 lba,
 		goto fail;
 	}
 
-	/* Check the GUID Partition Table header size */
+	/* Check the GUID Partition Table header size is too big */
 	if (le32_to_cpu((*gpt)->header_size) >
 			bdev_logical_block_size(state->bdev)) {
-		pr_debug("GUID Partition Table Header size is wrong: %u > %u\n",
+		pr_debug("GUID Partition Table Header size is too large: %u > %u\n",
 			le32_to_cpu((*gpt)->header_size),
 			bdev_logical_block_size(state->bdev));
 		goto fail;
 	}
 
+	/* Check the GUID Partition Table header size is too small */
+	if (le32_to_cpu((*gpt)->header_size) < sizeof(gpt_header)) {
+		pr_debug("GUID Partition Table Header size is too small: %u < %u\n",
+			le32_to_cpu((*gpt)->header_size),
+			sizeof(gpt_header));
+		goto fail;
+	}
+
 	/* Check the GUID Partition Table CRC */
 	origcrc = le32_to_cpu((*gpt)->header_crc32);
 	(*gpt)->header_crc32 = 0;
-- 
1.8.1.2