[PATCH] disk: gpt: verify alternate LBA points to last usable LBA

[Stefan Herbrechtsmeier]

From: Stefan Herbrechtsmeier <stefan.herbrechtsmeier at weidmueller.com>

The gpt command require the GPT backup header at the standard location
at the end of the device. Check the alternate LBA value before reading
the GPT backup header from the last usable LBA of the device.

Signed-off-by: Stefan Herbrechtsmeier <stefan.herbrechtsmeier at weidmueller.com>

---

 disk/part_efi.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/disk/part_efi.c b/disk/part_efi.c
index e5636ea7e6..0fb7ff0b6b 100644
--- a/disk/part_efi.c
+++ b/disk/part_efi.c
@@ -692,6 +692,15 @@ int gpt_verify_headers(struct blk_desc *dev_desc, gpt_header *gpt_head,
 	/* Free pte before allocating again */
 	free(*gpt_pte);
 
+	/*
+	 * Check that the alternate_lba entry points to the last LBA
+	 */
+	if (le64_to_cpu(gpt_head->alternate_lba) != (dev_desc->lba - 1)) {
+		printf("%s: *** ERROR: Misplaced Backup GPT ***\n",
+		       __func__);
+		return -1;
+	}
+
 	if (is_gpt_valid(dev_desc, (dev_desc->lba - 1),
 			 gpt_head, gpt_pte) != 1) {
 		printf("%s: *** ERROR: Invalid Backup GPT ***\n",
-- 
2.20.1