[PATCH 2/4] gpt: don't misbehave with e.g., a 9-entry partition array

[Jim Meyering]

From: Jim Meyering <address@hidden>

* libparted/labels/gpt.c (_generate_header): Correct size of
partition array entries to round up to nearest multiple of
sector size, so that we set gpt->PartitionEntryLBA correctly
also when the number of partition entries is not a multiple
of sector_size / 128.  Problem diagnosed by Robert Herndon
in http://thread.gmane.org/gmane.comp.gnu.parted.bugs/10173.
---
 NEWS                   |    5 +++++
 libparted/labels/gpt.c |    8 +++++---
 2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/NEWS b/NEWS
index b043ba1..c6e22f0 100644
--- a/NEWS
+++ b/NEWS
@@ -16,6 +16,11 @@ GNU parted NEWS                                    -*- 
outline -*-
   libparted: gpt_disk_duplicate now copies the flags over to the new
   disk object. Previously the flags would be undefined.

+  libparted can now read partition tables with a number of partition
+  array entries that is different from the default of 128.  Before,
+  it would fail to recognize them and could even read beyond the end
+  of a heap-allocated buffer.
+
   libparted: no longer aborts (failed assertion) due to a nilfs2_probe bug
   [bug introduced in parted-2.4 with the addition of nilfs2 support]

diff --git a/libparted/labels/gpt.c b/libparted/labels/gpt.c
index e239a2d..454a177 100644
--- a/libparted/labels/gpt.c
+++ b/libparted/labels/gpt.c
@@ -1137,13 +1137,15 @@ _generate_header (const PedDisk *disk, int alternate, 
uint32_t ptes_crc,

   if (alternate)
     {
-      PedSector ptes_size = gpt_disk_data->entry_count
-        * sizeof (GuidPartitionEntry_t) / disk->dev->sector_size;
+      size_t ss = disk->dev->sector_size;
+      PedSector ptes_bytes = (gpt_disk_data->entry_count
+                             * sizeof (GuidPartitionEntry_t));
+      PedSector ptes_sectors = (ptes_bytes + ss - 1) / ss;

       gpt->MyLBA = PED_CPU_TO_LE64 (disk->dev->length - 1);
       gpt->AlternateLBA = PED_CPU_TO_LE64 (1);
       gpt->PartitionEntryLBA
-        = PED_CPU_TO_LE64 (disk->dev->length - 1 - ptes_size);
+        = PED_CPU_TO_LE64 (disk->dev->length - 1 - ptes_sectors);
     }
   else
     {
-- 
1.7.8.rc0.32.g87bf9