Re: [sshfs] Issue mounting SSHFS'd home folder during login

[Miklos S. <mi...@sz...>]

On Tue, May 13, 2014 at 12:04 AM, IT Department <it...@om...> wrote:
> I've been using sshfs controlled by pam_mount to mount user's remote home
> folder to the local home folder on diskless terminals.  This was working
> fine using the version of ssh and sshfs included in Ubuntu 11.10, however
> using the version in 14.04 (sshfs 2.5, OpenSSH 6.6p1) the mount process
> locks up.
>
> Activating debug, and testing using the following test pattern it locks up
> after printing "executing <ssh> ...."
>
> # Test reproduction #
> Here's how I was able to test the situation, eliminating pam_mount and many
> other variables: (Caveat, I'm typing these commands into this email by hand
> - if there's typos, please correct!)
> 1. Create a test user (skip if you already have one) - for this procedure
> I'll call the username 'test'
> 2. Create the a user with the same name on a server.
> 3. Remove the test user's home folder: `rm -r /home/test`
> 4. Create an empty home folder, thus simulating what pam_mount does
> automatically: `mkdir /home/test; chown test:test /home/test`
> 5. Log in as the test user: `su - test`
> 6. Mount the user's home folder: `sshfs test@myserver:/home/test /home/test
> -o workaround=rename,nonempty,allow_other,nodev,nosuid`
> 7. Observe to see if the mount completes.
>
> The process hangs at step 7, thankfully a CTRL-C cancels it testing this
> way.  If pam_mount calls it during login...  that's another story.
>
> Note that after pressing CTL-C to cancel the process, you must execute
> `umount /home/test` to test again.
>
> # Thoughts #
> After some time of tweaking around with debug flags and other settings and
> observing the resulting behavior, it looks to me like the following is
> happening:
> 1. The mounting process gets some form of write lock on /home/test.
> 2. SSHFS then calls the SSH client with the SFTP subprotocol flag.
> 3. The SSH client then tries to get a readlock on (or even just read) some
> file in the current user's home folder: /home/test
>
> Of course, the writelock prevents all reads and readlocks in that
> mountpoint.
>
> I hope this was a clear enough description of the problem.  Thankfully it
> seems to constantly reproduce, indicating that there doesn't seem to be any
> race condition, just a sequence problem.

Please read back on the fuse-sshfs list archives, I remember having
discussed something similar some months ago...

If that doesn't help, then please get back to me.

Thanks,
Miklos