[devfs] Use before initialisation in devfs_mk_cdev()

From: Gergely Nagy (algernon@gandalph.mad.hu)
Date: Wed Jul 16 2003 - 18:53:42 EST


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.


Gergely Nagy
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This archive was generated by hypermail 2b29 : Wed Jul 23 2003 - 22:00:27 EST