Re: Bug with rewriting partition table - need help

[Jim Meyering]

Jim Meyering wrote:
> 27/249 wrote:
>> Seems that attached patch fixed this bug. I tested some cases, and
>> everything works fine for me, but I'm not sure if it can break
>> something hidden, so, developers, please review this fix.
>>
>> On Sun, Feb 7, 2010 at 6:50 PM, 27/249 <address@hidden> wrote:
>>> Yes, I forgot to add that this bug is still present in latest GIT tree
>>> (checked 1 minute ago).
>>>
>>> On Sun, Feb 7, 2010 at 6:48 PM, 27/249 <address@hidden> wrote:
>>>> Few weeks ago I described this bug in
>>>> http://parted.alioth.debian.org/cgi-bin/trac.cgi/ticket/250
>>>>
>>>> This bug is very serious for me, so, since I didn't see any motion in
>>>> bugtracker, I wish to try to fix it myself. If you can help me in any
>>>> way - it will be very good :) First of all, it will be very nice to
>>>> know what piece of code can commit partition table to disk.
>
> Thanks a lot for the report.
> That appears to be a serious bug.
>
> BTW, email to this mailing list will catch my attention,
> while I rarely look at that tracker.
>
> Would you please see if the patch below solves your problem?

He confirmed (off-list) that it solved the problem.
I have written a script to exercise the bug and a NEWS entry.
Here's the patch I expect to push soon.

>From c7cf12751993474238220593168dedfbbe18fc0a Mon Sep 17 00:00:00 2001
From: Jim Meyering <address@hidden>
Date: Sun, 7 Feb 2010 20:31:11 +0100
Subject: [PATCH] gpt: read-only operation could clobber MBR part of hybrid 
GPT+MBR table

* libparted/labels/gpt.c (gpt_read): Fix a bug introduced by me in
commit 7f753b1b, "gpt: rewrite GPT header-reading code".
Set write_back=0 in one more code path.
* tests/Makefile.am (TESTS): Add t0205-gpt-list-clobbers-pmbr.sh.
* tests/t0205-gpt-list-clobbers-pmbr.sh: New test.
* NEWS (Bug fixes): Mention this.
Reported by aix27249 in
http://parted.alioth.debian.org/cgi-bin/trac.cgi/ticket/250
---
 NEWS                                  |    5 +++
 libparted/labels/gpt.c                |   10 ++++--
 tests/Makefile.am                     |    1 +
 tests/t0205-gpt-list-clobbers-pmbr.sh |   59 +++++++++++++++++++++++++++++++++
 4 files changed, 72 insertions(+), 3 deletions(-)
 create mode 100644 tests/t0205-gpt-list-clobbers-pmbr.sh

diff --git a/NEWS b/NEWS
index ea6caa1..7b4994d 100644
--- a/NEWS
+++ b/NEWS
@@ -2,6 +2,11 @@ GNU parted NEWS                                    -*- outline 
-*-

 * Noteworthy changes in release ?.? (????-??-??) [?]

+** Bug fixes
+
+  gpt: read-only operation could clobber MBR part of hybrid GPT+MBR table
+  [bug introduced in parted-2.1]
+

 * Noteworthy changes in release 2.1 (2009-12-20) [stable]

diff --git a/libparted/labels/gpt.c b/libparted/labels/gpt.c
index 9d9876c..ea96a3b 100644
--- a/libparted/labels/gpt.c
+++ b/libparted/labels/gpt.c
@@ -4,7 +4,7 @@
     original version by Matt Domsch <address@hidden>
     Disclaimed into the Public Domain

-    Portions Copyright (C) 2001-2003, 2005-2009 Free Software Foundation, Inc.
+    Portions Copyright (C) 2001-2003, 2005-2010 Free Software Foundation, Inc.

     EFI GUID Partition Table handling
     Per Intel EFI Specification v1.02
@@ -932,9 +932,9 @@ gpt_read (PedDisk *disk)
   if (primary_gpt && backup_gpt)
     {
       /* Both are valid.  */
+#ifndef DISCOVER_ONLY
       if (PED_LE64_TO_CPU (primary_gpt->AlternateLBA) < disk->dev->length - 1)
         {
-#ifndef DISCOVER_ONLY
           switch (ped_exception_throw
                   (PED_EXCEPTION_ERROR,
                    (PED_EXCEPTION_FIX | PED_EXCEPTION_CANCEL
@@ -954,8 +954,12 @@ gpt_read (PedDisk *disk)
               write_back = 0;
               break;
             }
-#endif /* !DISCOVER_ONLY */
         }
+      else
+       {
+         write_back = 0;
+       }
+#endif /* !DISCOVER_ONLY */
       gpt = primary_gpt;
       pth_free (backup_gpt);
     }
diff --git a/tests/Makefile.am b/tests/Makefile.am
index 7bfb22e..38922f6 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -9,6 +9,7 @@ TESTS = \
   t0200-gpt.sh \
   t0201-gpt.sh \
   t0202-gpt-pmbr.sh \
+  t0205-gpt-list-clobbers-pmbr.sh \
   t0220-gpt-msftres.sh \
   t0250-gpt.sh \
   t0280-gpt-corrupt.sh \
diff --git a/tests/t0205-gpt-list-clobbers-pmbr.sh 
b/tests/t0205-gpt-list-clobbers-pmbr.sh
new file mode 100644
index 0000000..979a15e
--- /dev/null
+++ b/tests/t0205-gpt-list-clobbers-pmbr.sh
@@ -0,0 +1,59 @@
+#!/bin/sh
+# Ensure that printing a GPT partition table does not modify the pMBR.
+# Due to a bug in parted-2.1, "parted /dev/... print" would do just that.
+# Not a problem for most, but if you have a hybrid, e.g., gptsync'd
+# GPT/MBR table, merely listing the table with Parted-2.1 would clobber
+# the MBR part.
+
+# Copyright (C) 2010 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+if test "$VERBOSE" = yes; then
+  set -x
+  parted --version
+fi
+
+: ${srcdir=.}
+. $srcdir/t-lib.sh
+
+fail=0
+
+ss=$sector_size_
+n_sectors=400
+dev=dev-file
+
+dd if=/dev/null of=$dev bs=$ss seek=$n_sectors || fail=1
+parted -s $dev mklabel gpt                     || fail=1
+parted -s $dev mkpart p1 101s 150s             || fail=1
+parted -s $dev mkpart p2 151s 200s             || fail=1
+parted -s $dev mkpart p3 201s 250s             || fail=1
+
+parted -m -s $dev u s p                        || fail=1
+
+# Write non-NUL bytes all over the MBR, so we're likely to see any change.
+# However, be careful to leave the type of the first partition, 0xEE,
+# as well as the final two magic bytes.
+printf '%0450d\xee%059d\x55\xaa' 0 0 | dd of=$dev count=1 conv=notrunc || 
fail=1
+
+dd if=$dev of=before count=1 || fail=1
+
+chmod a-w $dev
+parted -m -s $dev u s p || fail=1
+
+dd if=$dev of=after count=1 || fail=1
+
+cmp before after || fail=1
+
+Exit $fail
--
1.7.0.rc2.156.g2ac04