[bug #24823] Partial sector disk writes are always corrupted

[David Simner]

URL:
  <http://savannah.gnu.org/bugs/?24823>

                 Summary: Partial sector disk writes are always corrupted
                 Project: GNU GRUB
            Submitted by: davidsimner
            Submitted on: Wed 12 Nov 2008 22:07:02 GMT
                Category: Disk &amp; Partition
                Severity: Major
                Priority: 5 - Normal
              Item Group: Software Error
                  Status: None
                 Privacy: Public
             Assigned to: None
         Originator Name: David Simner
        Originator Email: address@hidden
             Open/Closed: Open
         Discussion Lock: Any
                 Release: svn trunk at the time of writing
         Reproducibility: Every Time
         Planned Release: 

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Details:

In kern/disk.c if the grub_disk_write function is called to write data that
doesn't fill a whole sector [1], it will read the sector first using
grub_disk_read.

This causes a bug because grub_disk_read calls grub_disk_adjust_range, which
grub_disk_write has already called.

Therefore grub_disk_adjust_range will, for a second time, "Make sectors disk
relative from partition relative", and therefore grub_disk_read will read the
"wrong" sector, and hence grub_disk_write will subsequently corrupt the sector
it writes.

Please see the attached patch for a fix.

Cheers,

David

1. No-one seems to use this already existing feature of grub_disk_write.  I
happened to stumble upon this bug when I did.



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File Attachments:


-------------------------------------------------------
Date: Wed 12 Nov 2008 22:07:03 GMT  Name: patch  Size: 4kB   By: davidsimner

<http://savannah.gnu.org/bugs/download.php?file_id=16835>

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