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Re: [PATCH] Fix hang if $OLDPWD points to inaccessible directory


From: Mikulas Patocka
Subject: Re: [PATCH] Fix hang if $OLDPWD points to inaccessible directory
Date: Fri, 29 Sep 2017 11:12:59 +0200 (CEST)
User-agent: Alpine 2.02 (DEB 1266 2009-07-14)


On Thu, 28 Sep 2017, Eduardo A. Bustamante López wrote:

> On Thu, Sep 28, 2017 at 11:44:02AM +0200, Mikulas Patocka wrote:
> [...]
> > +++ bash/variables.c
> > @@ -899,7 +899,7 @@ set_pwd ()
> >       don't find OLDPWD in the environment, or it doesn't name a directory,
> >       make a dummy invisible variable for OLDPWD, and mark it as exported. 
> > */
> >    temp_var = find_variable ("OLDPWD");
> > -  if (temp_var == 0 || value_cell (temp_var) == 0 || file_isdir 
> > (value_cell (temp_var)) == 0)
> > +  if (temp_var == 0 || value_cell (temp_var) == 0)
> >      {
> >        temp_var = bind_variable ("OLDPWD", (char *)NULL, 0);
> 
> This patch would revert the change introduced in:
>   
> http://git.savannah.gnu.org/cgit/bash.git/commit/?h=devel&id=e6f5e0c858b7c0839d346d7d55e56894648c5a33

This patch doesn't revert the above change. It only removes a test if 
$OLDPWD is a directory. With this patch, if $OLDPWD points to a directory, 
there will be no change, and if $OLDPWD points to non-directory, it will 
not be cleared.

> Which was prompted by the following bug report from John Wiersba:
>   https://lists.gnu.org/archive/html/bug-bash/2015-11/msg00115.html
> 
> Correct me if I'm wrong, but a hanged sshfs mount will cause many more
> issues, not only with OLDPWD.

Hung mount shouldn't cause problems unless someone is accessing it.

What happened to me - I use the autofs filesystem to automatically mount 
filesystems on various machines. I was on some autofs-mounted directory, I 
moved to the home directory (which is not on autofs) and I typed startx. 
Some times after that I shut down the remote machine that provided the 
autofs mount.

The whole X session started to severely mibehave, starting various 
programs caused hangs, I couldn't even start an xterm with the shell, I 
couldn't even start the chome browser - the reason for the hangs was, that 
the OLDPWD variable pointing to the autofs directory ended up being 
propagated to the Xserver, to the desktop environment and to any program 
that was running within the X session. I caused serious trouble and I 
think it should be fixed.

If I started Xwindow on the non-functioning autofs directory, it would be 
expected that I get hangs. However, I started Xwindow in the home 
directory that has nothing to do with autofs - and I got hangs.

Mikulas


> I tried the following:
> 
> address@hidden:~/test$ ls -l
> total 4
> drwxr-xr-x 2 dualbus dualbus 4096 sep 28 10:05 host
> address@hidden:~/test$ sshfs $host: host
> address@hidden:~/test$ ls -ld host
> drwxr-xr-x 1 dualbus dualbus 20480 sep 28 08:15 host
> address@hidden:~/test$ cd host
> address@hidden:~/test/host$ pwd
> /home/dualbus/test/host
> address@hidden:~/test/host$ cd ..
> address@hidden:~/test$ df host | sed "s/$host/<host>/"
> Filesystem     1K-blocks     Used Available Use% Mounted on
> <host>:     20511592 13003368   6452528  67% /home/dualbus/test/host
> address@hidden:~/test$ sudo iptables -A OUTPUT -p tcp -d $host -j DROP
> address@hidden:~/test$ ls
> ^C^C^C^C^C
> 
> Also tried:
> 
> cd ho<TAB> # hangs
> cd host # hangs
> ls -l host # hangs
> 
> So in my opinion, it's not worth to revert this change given that you'll have
> many more troubles with a hanged network filesystem.
> 


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