sharing a partition betweed FC3 and FC5

[D. Hugh Redelmeier]

I installed 32-bit Fedora Core 5 on an Athlon-64 box.  I intended this
installation to co-exist with a 64-bit Fedora Core 3 installation.
The two installations share a /home ext3 partition and the swap partition.
This is often how I do upgrades: a dual boot system with both old and
new bootable.

The problem is that the FC5 installation did something to
the /home partition that prevents the FC3 from mounting it.

When I manually try a mount of /home from FC3, the useless
mount-failure message is preceded by these messages.  I think that
they are the key:

inode_doinit_with_dentry:  context_to_sid(system_u:object_r:home_root_t:s0) returned 22 for dev=hda5 ino=2
    inode_doinit_with_dentry:  context_to_sid(system_u:object_r:home_root_t:s0) returned 22 for dev=hda5 ino=2

(In dmesg, these two messages were preceded by these that might be relevant:
    kjournald starting.  Commit interval 5 seconds
    EXT3 FS on hda5, internal journal
    EXT3-fs: mounted filesystem with ordered data mode.
    SELinux: initialized (dev hda5, type ext3), uses xattr
)

(The useless mount failure message is:
  mount: wrong fs type, bad option, bad superblock on /dev/hda5
         or too many mounted file systems
 This message is disgracefully non-specific.)

I think that this is a problem with SELinux.  The following thread
looks relevant but unhelpful:
  http://www.redhat.com/archives/fedora-selinux-list/2006-April/msg00002.html
It provides a solution (I hope) for FC4 but FC3 would not have such an update.

I tried using enforcing=0 on the FC3 kernel command line, but nothing changed.

I thought ext3 was compatible between Fedora releases.  Unfortunately,
SELinux seems to have made things a lot more brittle.

==> Is there something simple that I can do to allow the existing
    /home ext3 partition to be shared between FC3 and FC5?

==> What does the error message mean?
    inode 2 is the root of the filesystem.
    It appears that kernel routine inode_doinit_with_dentry is calling context_to_sid
    and context_to_sid is returning EINVAL (because the context was invalid).
    But even knowing that, I don't know what it actually means or is caused by.

(By the way, if FC5 worked well, it might not matter.  Unfortunately,
there is some regression in xorg that prevents dual-head working
properly on FC5 where it did on FC3.)

[Andy Burns]

D. Hugh Redelmeier wrote:
> The problem is that the FC5 installation did something to
> the /home partition that prevents the FC3 from mounting it.

Does this help?
http://fedora.redhat.com/docs/selinux-faq-fc5/#id2963134

[D. Hugh Redelmeier]

| From: Andy Burns

| D. Hugh Redelmeier wrote:
| 
| > The problem is that the FC5 installation did something to
| > the /home partition that prevents the FC3 from mounting it.
| 
| Does this help?
| http://fedora.redhat.com/docs/selinux-faq-fc5/#id2963134

This particulare FAQ entry doesn't seem to match my experience.

We can log in with FC5.  So it must have relabelled /home.

On the other hand, FC3 can no longer mount /home.  It isn't just a
problem of preventing users from logging in.  In fact, users can still
log in, with the limitation that they have no home directory.

Maybe I can relabel /home in FC3.  That *might* let FC3 mount /home
(I'm not sure -- I don't actually understand the error message).  If
it does, surely FC5 will no longer like /home.

[Tony Nelson]

At 11:22 AM -0400 8/6/06, D. Hugh Redelmeier wrote:
> | From: Andy Burns
>
> | D. Hugh Redelmeier wrote:
> |
> | > The problem is that the FC5 installation did something to
> | > the /home partition that prevents the FC3 from mounting it.
> |
> | Does this help?
> | http://fedora.redhat.com/docs/selinux-faq-fc5/#id2963134
>
> This particulare FAQ entry doesn't seem to match my experience.
>
> We can log in with FC5.  So it must have relabelled /home.
>
> On the other hand, FC3 can no longer mount /home.  It isn't just a
> problem of preventing users from logging in.  In fact, users can still
> log in, with the limitation that they have no home directory.
>
> Maybe I can relabel /home in FC3.  That *might* let FC3 mount /home
> (I'm not sure -- I don't actually understand the error message).  If
> it does, surely FC5 will no longer like /home.

I expect so.  Relabeling each time would be slow.

Try booting FC3 with "enforcing=0" appended to the kernel command line.  If
that works, then you have established that it is an SELinux issue.

If it is an SELinux issue, I think you will need to either not use SELinux
on one of the installations, or use the same SELinux and SELinux Policy in
both.  That would probably require using the same kernel in both (but what
do I know?).

Even if you do manage to share /home, you might also face issues with the
shared .configuration files.  You might wish to share something lower down
inside each user's account.  I have not faced this issue yet myself; I just
have two copies of everything.  This works because I don't use FC3 anymore;
I'll blow it away soon for FC6.
____________________________________________________________________
TonyN.:'                       
      '                              http://www.georgeanelson.com/

[D. Hugh Redelmeier]

| From: D. Hugh Redelmeier

| ==> Is there something simple that I can do to allow the existing
|     /home ext3 partition to be shared between FC3 and FC5?

I also posted the query to the fedora-selinux list.  The answers I got
were quite useful.  The thread starts here:
  https://www.redhat.com/mailman/listinfo/fedora-selinux-list

Paul Howarth (well known on this list) explained that the structure
used to record file contexts in FC5 is larger than that for FC3 (or
unpatched FC4).  So that isn't easy to fix.

Stephen Smalley (one of the SELinux authors at the NSA) said that
kernel patching or turning off SELinux in FC3 were the two available
options.

I don't think that there is a patched kernel version available "off
the shelf" for FC3.  Besides, the whole reason for keeping FC3 is to
have a "known good" kernel to fall back to when something goes wrong.
Patching the kernel eliminates the "known good" classification :-)

My guess is that turning off SELinux in FC3 will result in a bit of a
mess when I'm reboot in FC5 with SELinux.  Will /home need to be
relabelled?  I will ask on the fedora-selinux.

Thanks for your help.