Re: [PATCH 1/2] exec: Make do_coredump more robust and safer when using pipes in core_pattern: recursive dump detection

Neil Horman
2009-06-26T20:24:27Z

On Fri, Jun 26, 2009 at 06:59:08PM +0200, Oleg Nesterov wrote:
> On 06/26, Neil Horman wrote:
> >
> > + if (core_limit == 0) {
> > + /*
> > + * Normally core limits are irrelevant to pipes, since
> > + * we're not writing to the file system, but we use
> > + * core_limit of 0 here as a speacial value. Any
> > + * non-zero limit gets set to RLIM_INFINITY below, but
> > + * a limit of 0 skips the dump. This is a consistent
> > + * way to catch recursive crashes. We can still crash
> > + * if the core_pattern binary sets RLIM_CORE = !0
> > + * but it runs as root, and can do lots of stupid things
> > + * Note that we use task_tgid_vnr here to grab the pid of the
> > + * process group leader. That way we get the right pid if a thread
> > + * in a multi-threaded core_pattern process dies.
> > + */
> > + printk(KERN_WARNING "Process %d(%s) has RLIMIT_CORE set to 0\n",
> > + task_tgid_vnr(current), current->comm);
> > + printk(KERN_WARNING "Aborting core\n");
>
> Andrew has already pointed out this, unprivileged-user-triggerable
> printk.
>
> Doesn't look good, if core_pattern starts with "|" any user can set
> RLIMIT_CORE = 0 and then just do
>
> for (;;)
> if (pid = fork())
> kill(pid, SIGQUIT);
>
> to DOS printk/syslog, no?
>
I don't think SIGQUIT will trigger this, but SIGSEGV will. Regardless, if you
do that, I would think you have bigger problems on your system. I would be
silent about this, but I'm not sure thats a better solution

Neil

> Oleg.
>
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