Re: Potential regression in -git15: can't resume stopped root shell?

[Theodore Tso <tytso@mit.edu>]

On Sat, Oct 20, 2007 at 02:58:06PM -0400, Theodore Tso wrote:
> I was testing 2.6.23-git15, and I'm noticing that if I su to root, then
> suspend the root shell, and try continue it via "fg", it hangs.  The ps
> command reports:
> 
> 15806  6386  19   0  4012 wait                 Ss   pts/0    00:00:00 bash
>     0  6444  19   0  1232 finish_stop          T+   pts/0    00:00:00 /bin/su -p
>     0  6445  19   0  3696 finish_stop          T    pts/0    00:00:00 bash
> 15806  6571  19   0   776 pipe_wait            S+   pts/1    00:00:00 grep pts/0
> 
> This works under 2.6.23.  I am running Ubuntu Gutsy running in a
> gnome-terminal, with bash as my login shell.  I can suspend a zsh or
> bash shell where I haven't su'ed to root.  But if the shell is started
> using either su or sudo, when I try to resume it after suspending
> using the "suspend" command via "fg", I get a hung shell.
> 
> I haven't had time to bisect it yet, but I thought I'd throw it out
> there in case this rings a bell with anybody...

OK, I bisected, and it turns out to be a bug, but not a regression.
Turns out the responsible commit is:

commit b53767719b6cd8789392ea3e7e2eb7b8906898f0
Author: Serge E. Hallyn <serue@us.ibm.com>
Date:   Tue Oct 16 23:31:36 2007 -0700

    Implement file posix capabilities
    
    Implement file posix capabilities.  This allows programs to be given a
    subset of root's powers regardless of who runs them, without having to use
    setuid and giving the binary all of root's powers.....

Once I turned this up, I turned went back to -git15, and turned off
CONFIG_SECURITY_FILE_CAPABILITIES, and the problem went away.  Oh,
well, I had wanted to try out file capabilities, which is why I had
turned the option on, but being able to resume suspended root shells
is more important.  :-)

Serge, can you take a look at this, please?  Thanks!!

						- Ted