[devfs] Use before initialisation in devfs_mk_cdev()

[Gergely Nagy <algernon@gandalph.mad.hu>]

Hi!

While playing around with implementing my first linux 2.5 module, I
stumbled upon a buglet in devfs (though, if used properly, it probably
won't surface ever). The problem - as I see it - is that
devfs_mk_cdev() first checks the mode passed to it, and if it thinks
it is not a char device, it prints a warning and aborts. Now, this
printing involves the local variable `buf' (char buf[64]), which is
not initialised at that point.

The problematic code is:

int devfs_mk_cdev(dev_t dev, umode_t mode, const char *fmt, ...)
{
	struct devfs_entry *dir = NULL, *de;
	char buf[64];
	va_list args;
	int error, n;

	if (!S_ISCHR(mode)) {
		printk(KERN_WARNING "%s: invalide mode (%u) for %s\n",
				__FUNCTION__, mode, buf);
		return -EINVAL;
	}

One option would be to try to initialise buf earlier, another would be
to just remove the "for %s" part, and the buf reference in the printk
(but that way, some information would be lost).

Anyways, I just noticed that when my buggy code called devfs_mk_cdev
(blah, 0, etc..) it printed garbage on module insertion, so I thought
I'd drop a notice.

Oh, this is with Linux 2.6.0-test1-mm1.

Cheers,
-- 
Gergely Nagy