Re: Interesting race condition...

[Roger Luethi <rl@hellgate.ch>]

On Thu, 22 Jul 2004 22:04:46 -0500, Rob Landley wrote:
> I just saw a funky thing.  Here's the cut and past from the xterm...
> 
> [root@(none) root]# ps ax | grep hack
>  9964 pts/1    R      0:00 grep hack HOSTNAME= SHELL=/bin/bash TERM=xterm HISTSIZE=1000 USER=root LS_COLORS=no=00:fi=00:di=00;34:ln=00;36:pi=40;33:so=00;35:bd=40;33;01:cd=40;33;01:or=01;05;37;41:mi=01;05;37;41:ex=00;32:*.cmd=00;32:*.exe=00;32:*.com=00;32:*.btm=00;32:*.bat=00;32:*.sh=00;32:*.csh=00;32:*.tar=00;31:*.tgz=
> [root@(none) root]# ps ax | grep hack
>  9966 pts/1    S      0:00 grep hack
> 
> Seems like some kind of race condition, dunno if it's in Fedore Core 1's ps
> or the 2.6.7 kernel or what...

If somebody posted a solution for this, I didn't see it. There's a race in
the kernel, and considering the permissions on /proc/PID/{cmdline,environ}
a security bug as well: If you win the race with a starting process, you
can read its environment.

This should plug the hole. Can you give it a spin?

Roger

--- linux-2.6.8-rc2-bk1/fs/proc/base.c.orig	2004-07-30 01:43:23.535967505 +0200
+++ linux-2.6.8-rc2-bk1/fs/proc/base.c	2004-07-30 01:43:27.428303752 +0200
@@ -329,6 +329,8 @@ static int proc_pid_cmdline(struct task_
 	struct mm_struct *mm = get_task_mm(task);
 	if (!mm)
 		goto out;
+	if (!mm->arg_end)
+		goto out;	/* Shh! No looking before we're done */
 
  	len = mm->arg_end - mm->arg_start;