Subject: Re: [PATCH v4 4/6] mm/slab: Introduce kmem_buckets_create() and family

From: Kees Cook <[email-masked]>
Date: Tue, 4 Jun 2024 17:49:20 -0700

On Tue, Jun 04, 2024 at 04:13:32PM -0600, Tycho Andersen wrote:
> On Tue, Jun 04, 2024 at 04:02:28PM +0100, Simon Horman wrote:
> > On Fri, May 31, 2024 at 12:14:56PM -0700, Kees Cook wrote:
> > > +	for (idx = 0; idx < ARRAY_SIZE(kmalloc_caches[KMALLOC_NORMAL]); idx++) {
> > > +		char *short_size, *cache_name;
> > > +		unsigned int cache_useroffset, cache_usersize;
> > > +		unsigned int size;
> > > +
> > > +		if (!kmalloc_caches[KMALLOC_NORMAL][idx])
> > > +			continue;
> > > +
> > > +		size = kmalloc_caches[KMALLOC_NORMAL][idx]->object_size;
> > > +		if (!size)
> > > +			continue;
> > > +
> > > +		short_size = strchr(kmalloc_caches[KMALLOC_NORMAL][idx]->name, '-');
> > > +		if (WARN_ON(!short_size))
> > > +			goto fail;
> > > +
> > > +		cache_name = kasprintf(GFP_KERNEL, "%s-%s", name, short_size + 1);
> > > +		if (WARN_ON(!cache_name))
> > > +			goto fail;
> > > +
> > > +		if (useroffset >= size) {
> > > +			cache_useroffset = 0;
> > > +			cache_usersize = 0;
> > > +		} else {
> > > +			cache_useroffset = useroffset;
> > > +			cache_usersize = min(size - cache_useroffset, usersize);
> > > +		}
> > > +		(*b)[idx] = kmem_cache_create_usercopy(cache_name, size,
> > > +					align, flags, cache_useroffset,
> > > +					cache_usersize, ctor);
> > > +		kfree(cache_name);
> > > +		if (WARN_ON(!(*b)[idx]))
> > > +			goto fail;
> > > +	}
> > > +
> > > +	return b;
> > > +
> > > +fail:
> > > +	for (idx = 0; idx < ARRAY_SIZE(kmalloc_caches[KMALLOC_NORMAL]); idx++) {
> > > +		if ((*b)[idx])
> > > +			kmem_cache_destroy((*b)[idx]);
> > 
> > nit: I don't think it is necessary to guard this with a check for NULL.
> 
> Isn't it? What if a kasprintf() fails halfway through the loop?

He means that kmem_cache_destroy() already checks for NULL. Quite right!

void kmem_cache_destroy(struct kmem_cache *s)
{
        int err = -EBUSY;
        bool rcu_set;

        if (unlikely(!s) || !kasan_check_byte(s))
                return;

-- 
Kees Cook