linux-kernel - broken daemonize (COW credentials?)

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Message-ID: <496535D9.6040606@gmail.com>
Date:	Thu, 08 Jan 2009 00:08:09 +0100
From:	Jiri Slaby <jirislaby@...il.com>
To:	David Howells <dhowells@...hat.com>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	James Morris <jmorris@...ei.org>
Subject: broken daemonize (COW credentials?)

Hi,

I'm observing daemonize crashes with this code:
static struct pid *pid;
static DECLARE_COMPLETION(comp);

static int bubak(void *data)
{
        daemonize("bubak");
        while (!signal_pending(current))
                msleep_interruptible(5000);
        complete_and_exit(&comp, 0);
        return 0;
}

static int init1(void) <-- module_init function
{
        int ret;

        ret = kernel_thread(bubak, NULL, 0);
        if (ret < 0)
                return ret;
        pid = find_get_pid(ret);
	return 0;
}
----------------------- cut here -------------------

This is due to:
daemonize
 -> exit_mm
   -> tsk->mm = NULL; (i.e. current->mm)
 -> reparent_to_kthreadd
   -> commit_creds
     -> set_dumpable(task->mm, suid_dumpable); (i.e. current->mm)

The culprit is probably COW credentials. David?
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