Re: [PATCH 2/2] s390/iucv: Fix vargs handling in iucv_alloc_device()

Vasily Gorbik
2024-08-13T11:50:42Z

On Tue, Aug 13, 2024 at 12:52:19PM +0200, Greg Kroah-Hartman wrote:
> On Tue, Aug 13, 2024 at 12:42:37PM +0200, Vasily Gorbik wrote:
> > From: Heiko Carstens <hca@linux.ibm.com>
> >
> > iucv_alloc_device() gets a format string and a varying number of
> > arguments. This is incorrectly forwarded by calling dev_set_name() with
> > the format string and a va_list, while dev_set_name() expects also a
> > varying number of arguments.
> >
> > Fix this and call kobject_set_name_vargs() instead which expects a
> > va_list parameter.
>
> I don't understand, why can't dev_set_name() be called here?
>
> Calling "raw" kobject functions is almost never the correct thing to be
> doing, ESPECIALLY as you have a struct device here.

struct device *iucv_alloc_device(const struct attribute_group **attrs,
void *priv, const char *fmt, ...);

va_start(vargs, fmt); initializes vargs to point to the first argument after fmt.

__printf(2, 0) int kobject_set_name_vargs(struct kobject *kobj, const char *fmt, va_list vargs);

__printf(2, 3) int dev_set_name(struct device *dev, const char *name, ...);

dev_set_name is expecting to receive individual variable arguments
directly (...), not a va_list.

The (...) in dev_set_name is meant to be expanded into individual
arguments, but when you pass a va_list to it, this expansion doesn't
happen. Instead, the va_list is just treated as a pointer or a single
argument, leading to undefined or incorrect behavior.

So, would it be okay to reuse kobject_set_name_vargs() here, or would you propose
introducing another helper just for this case? e.g.

int dev_set_name_vargs(struct device *dev, const char *fmt, va_list vargs)
{
჻·······return kobject_set_name_vargs(&dev->kobj, fmt, vargs);
}
EXPORT_SYMBOL_GPL(dev_set_name_vargs)

The bz link should be:
Link: https://bugzilla.suse.com/show_bug.cgi?id=1228425