[parted-devel] [PATCH 1/2] libparted: check PMBR before GPT partition table (#805272)

[Brian C. Lane]

From: "Brian C. Lane" <bcl at redhat.com>

The UEFI spec requires that a valid GPT disk label have a PMBR
partition. This moves the PMBR check to before the GPT check,
exiting gpt_probe with a 0 if the PMBR is not valid.

The previous behavior would cause problems in the following situation:
 1. format a disk as GPT
 2. re-format it as MSDOS using tools that don't understand GPT

Subsequent operations with parted would then complain about the invlid
PMBR, but would not allow the disk to be used as a msdos disk. This
change causes parted to tread the disk as a msdos disk.

* libparted/labels/gpt.c (gpt_probe): Move _pmbr_is_valid test
---
 libparted/labels/gpt.c |   44 +++++++++++++-------------------------------
 1 files changed, 13 insertions(+), 31 deletions(-)

diff --git a/libparted/labels/gpt.c b/libparted/labels/gpt.c
index 84bdc12..e57b3a2 100644
--- a/libparted/labels/gpt.c
+++ b/libparted/labels/gpt.c
@@ -465,6 +465,17 @@ gpt_probe (const PedDevice *dev)
   if (dev->length <= 1)
     return 0;
 
+  void *label;
+  if (!ptt_read_sector (dev, 0, &label))
+    return 0;
+
+  if (!_pmbr_is_valid ((const LegacyMBR_t *) label))
+    {
+        free (label);
+        return 0;
+    }
+  free (label);
+
   void *pth_raw = ped_malloc (pth_get_size (dev));
   if (ped_device_read (dev, pth_raw, 1, GPT_HEADER_SECTORS)
       || ped_device_read (dev, pth_raw, dev->length - 1, GPT_HEADER_SECTORS))
@@ -472,40 +483,11 @@ gpt_probe (const PedDevice *dev)
       gpt = pth_new_from_raw (dev, pth_raw);
       if (gpt->Signature == PED_CPU_TO_LE64 (GPT_HEADER_SIGNATURE))
         gpt_sig_found = 1;
+      pth_free (gpt);
     }
-
   free (pth_raw);
 
-  pth_free (gpt);
-
-  if (!gpt_sig_found)
-    return 0;
-
-  void *label;
-  if (!ptt_read_sector (dev, 0, &label))
-    return 0;
-
-  int ok = 1;
-  if (!_pmbr_is_valid ((const LegacyMBR_t *) label))
-    {
-      int ex_status = ped_exception_throw
-        (PED_EXCEPTION_WARNING,
-         PED_EXCEPTION_YES_NO,
-         _("%s contains GPT signatures, indicating that it has "
-           "a GPT table.  However, it does not have a valid "
-           "fake msdos partition table, as it should.  Perhaps "
-           "it was corrupted -- possibly by a program that "
-           "doesn't understand GPT partition tables.  Or "
-           "perhaps you deleted the GPT table, and are now "
-           "using an msdos partition table.  Is this a GPT "
-           "partition table?"),
-         dev->path);
-      if (ex_status == PED_EXCEPTION_NO)
-        ok = 0;
-    }
-
-  free (label);
-  return ok;
+  return gpt_sig_found;
 }
 
 static PedDisk *
-- 
1.7.7.6