[Rdiff-backup-bugs] [bug #26796] Hardlinked files not backed up because of UpdateError/Updated mirror temp file does not match source

[Joe Steele]

URL:
  <http://savannah.nongnu.org/bugs/?26796>

                 Summary: Hardlinked files not backed up because of
UpdateError/Updated mirror temp file does not match source
                 Project: rdiff-backup
            Submitted by: j_steele
            Submitted on: Sat 13 Jun 2009 08:23:55 PM GMT
                Category: None
                Severity: 3 - Normal
              Item Group: None
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any

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Details:

When I attempted to back up a CentOS-4 system to a CentOS-5 system using
rdiff-backup v. 1.2.8, all of the hard-linked files were omitted from the
backup with errors saying "Updated mirror temp file does not match source".

A couple specific examples of the errors:

| UpdateError bin/gzip Updated mirror temp file
/var/lib/safekeep/lan3/bin/rdiff-backup.tmp.40 does not match source
| UpdateError bin/zcat Updated mirror temp file
/var/lib/safekeep/lan3/bin/rdiff-backup.tmp.101 does not match source

Looking at the source system (CentOS-4), I see that gunzip, gzip, and zcat
are hardlinked:


| address@hidden ~]# stat /bin/{gunzip,gzip,zcat}
|   File: `/bin/gunzip'
|   Size: 56080           Blocks: 128        IO Block: 4096   regular file
| Device: fd07h/64775d    Inode: 61202       Links: 3
| Access: (0755/-rwxr-xr-x)  Uid: (    0/    root)   Gid: (    0/    root)
| Access: 2009-06-13 04:02:12.000000000 -0400
| Modify: 2007-07-14 17:37:33.000000000 -0400
| Change: 2008-12-02 17:58:06.000000000 -0500
|   File: `/bin/gzip'
|   Size: 56080           Blocks: 128        IO Block: 4096   regular file
| Device: fd07h/64775d    Inode: 61202       Links: 3
| Access: (0755/-rwxr-xr-x)  Uid: (    0/    root)   Gid: (    0/    root)
| Access: 2009-06-13 04:02:12.000000000 -0400
| Modify: 2007-07-14 17:37:33.000000000 -0400
| Change: 2008-12-02 17:58:06.000000000 -0500
|   File: `/bin/zcat'
|   Size: 56080           Blocks: 128        IO Block: 4096   regular file
| Device: fd07h/64775d    Inode: 61202       Links: 3
| Access: (0755/-rwxr-xr-x)  Uid: (    0/    root)   Gid: (    0/    root)
| Access: 2009-06-13 04:02:12.000000000 -0400
| Modify: 2007-07-14 17:37:33.000000000 -0400
| Change: 2008-12-02 17:58:06.000000000 -0500
| 


On the destination system (CentOS-5), the only file backed up (of these 3)
was /bin/gunzip.  The other 2 were omitted because of the errors above. In
all, there were 17,706 of these errors during the backup, all resulting from
hardlinked files (as best I can tell -- I didn't do an exhaustive review of
them).  The backup was made using LVM snapshot devices, so it wasn't a case of
errors caused by files being changed during the backup.

Upon further investigation, I found that this bug is triggered by a
difference in the way selinux attributes are saved under CentOS-4 vs. CentOS-5
(and yes, the backup included extended attributes and both systems use
selinux).  Here's an example of the attributes on each system:

On CentOS-4:
| address@hidden ~]# getfattr -d -m '' /bin/gunzip
| getfattr: Removing leading '/' from absolute path names
| # file: bin/gunzip
| security.selinux="system_u:object_r:bin_t\000"

On CentOS-5:
| address@hidden ~]# getfattr -d -m '' /bin/gunzip
| getfattr: Removing leading '/' from absolute path names
| # file: bin/gunzip
| security.selinux="system_u:object_r:bin_t:s0\000"

As shown, CentOS-5 adds ":s0" to all of its selinux attributes.  This was
triggering a bug in rdiff-backup, making it conclude that the source and
destination hardlinks didn't match (which technically is true, but shouldn't
matter since the attributes and other metadata are saved separately by
rdiff-backup).

I am attaching a patch for backup.py (v. 1.2.8) that seemed to fix this bug
for me.  With it, I could back up hardlinked files without error, and I could
restore them with their original attributes intact.  I am not expert in the
ways of rdiff-backup (or python in general), so this patch should be
scrutinized by others with more expertise than me.  I have not, for example,
investigated whether regressions of failed backups work properly.

This bug is triggered regardless of which direction the backup is made, and
regardless of which system is the initiator of the backup.  I have also
triggered the bug by putting phony security.selinux attributes on a couple
hardlinked files on a non-selinux system (e.g., a sysrecuecd live CD), and
then backed up the files to a selinux system (e.g., CentOS-4 or CentOS-5).




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File Attachments:


-------------------------------------------------------
Date: Sat 13 Jun 2009 08:23:55 PM GMT  Name: backup.py.patch.txt  Size: 616B 
 By: j_steele

<http://savannah.nongnu.org/bugs/download.php?file_id=18258>

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