libfdisk: (gpt) cleanup header size usage

Kay reported that Windows 8.1 installed does not recognize GPT created
by libfdisk, but parted works as expected.

It seems (according to the header hexdump) that the problem is
HeaderSize GPT field where libfdisk uses 512 (header + reserved area),
but parted uses 92. The both is pretty valid according to the current
EFI standard, but 92 is probably more backwardly compatible.

I also found places in code where libfdisk gpt driver is inconsistent
and uses sometimes all sector and simetimes sizeof(gpt_header) only.
The right solution is to read all sector (into zeroized memory) and
later write again all sector to the device.

Reported-by: Kay Sievers <kay@vrfy.org>
Signed-off-by: Karel Zak <kzak@redhat.com>

1 files changed, 26 insertions, 7 deletions

diff --git a/libfdisk/src/gpt.c b/libfdisk/src/gpt.c
index 8c1c96c37..f6e1741e2 100644
--- a/libfdisk/src/gpt.c
+++ b/libfdisk/src/gpt.c
@@ -484,7 +484,9 @@ static struct gpt_header *gpt_copy_header(struct fdisk_context *cxt,
 	if (!cxt || !src)
 		return NULL;
 
-	res = calloc(1, sizeof(*res));
+	assert(cxt->sector_size >= sizeof(struct gpt_header));
+
+	res = calloc(1, cxt->sector_size);
 	if (!res) {
 		fdisk_warn(cxt, _("failed to allocate GPT header"));
 		return NULL;
@@ -551,7 +553,14 @@ static int gpt_mknew_header(struct fdisk_context *cxt,
 
 	header->signature = cpu_to_le64(GPT_HEADER_SIGNATURE);
 	header->revision  = cpu_to_le32(GPT_HEADER_REVISION_V1_00);
-	header->size      = cpu_to_le32(sizeof(struct gpt_header));
+
+	/* According to EFI standard it's valid to count all the first
+	 * sector into header size, but some tools may have a problem
+	 * to accept it, so use the header without the zerozied area.
+	 * This does not have any impact to CRC, etc.   --kzak Jan-2015
+	 */
+	header->size = cpu_to_le32(sizeof(struct gpt_header)
+				- sizeof(header->reserved2));
 
 	/*
 	 * 128 partitions are the default. It can go beyond that, but
@@ -863,12 +872,16 @@ static struct gpt_header *gpt_read_header(struct fdisk_context *cxt,
 	if (!cxt)
 		return NULL;
 
-	header = calloc(1, sizeof(*header));
+	/* always allocate all sector, the area after GPT header
+	 * has to be fill by zeros */
+	assert(cxt->sector_size >= sizeof(struct gpt_header));
+
+	header = calloc(1, cxt->sector_size);
 	if (!header)
 		return NULL;
 
 	/* read and verify header */
-	if (read_lba(cxt, lba, header, sizeof(struct gpt_header)) != 0)
+	if (read_lba(cxt, lba, header, cxt->sector_size) != 0)
 		goto invalid;
 
 	if (!gpt_check_signature(header))
@@ -1630,7 +1643,11 @@ fail:
 }
 
 /*
- * Write a GPT header to a specified LBA
+ * Write a GPT header to a specified LBA.
+ *
+ * We read all sector, so we have to write all sector back
+ * to the device -- never ever rely on sizeof(struct gpt_header)!
+ *
  * Returns 0 on success, or corresponding error otherwise.
  */
 static int gpt_write_header(struct fdisk_context *cxt,
@@ -2182,8 +2199,10 @@ static int gpt_create_disklabel(struct fdisk_context *cxt)
 	if (rc < 0)
 		goto done;
 
+	assert(cxt->sector_size >= sizeof(struct gpt_header));
+
 	/* primary */
-	gpt->pheader = calloc(1, sizeof(*gpt->pheader));
+	gpt->pheader = calloc(1, cxt->sector_size);
 	if (!gpt->pheader) {
 		rc = -ENOMEM;
 		goto done;
@@ -2193,7 +2212,7 @@ static int gpt_create_disklabel(struct fdisk_context *cxt)
 		goto done;
 
 	/* backup ("copy" primary) */
-	gpt->bheader = calloc(1, sizeof(*gpt->bheader));
+	gpt->bheader = calloc(1, cxt->sector_size);
 	if (!gpt->bheader) {
 		rc = -ENOMEM;
 		goto done;