linux-kernel - Re: [PATCH 1/2] kasan: fix crashes on access to memory mapped by vm_map

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Date:   Wed, 4 Dec 2019 23:40:37 +0100
From:   Uladzislau Rezki <urezki@...il.com>
To:     Andrey Ryabinin <aryabinin@...tuozzo.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>, kasan-dev@...glegroups.com,
        Daniel Axtens <dja@...ens.net>, Qian Cai <cai@....pw>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        syzbot+82e323920b78d54aaed5@...kaller.appspotmail.com
Subject: Re: [PATCH 1/2] kasan: fix crashes on access to memory mapped by
 vm_map_ram()

> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 4d3b3d60d893..a5412f14f57f 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -1073,6 +1073,7 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
>  	struct vmap_area *va, *pva;
>  	unsigned long addr;
>  	int purged = 0;
> +	int ret = -EBUSY;
>  
>  	BUG_ON(!size);
>  	BUG_ON(offset_in_page(size));
> @@ -1139,6 +1140,10 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
>  	va->va_end = addr + size;
>  	va->vm = NULL;
>  
> +	ret = kasan_populate_vmalloc(addr, size);
> +	if (ret)
> +		goto out;
> +
But it introduces another issues when is CONFIG_KASAN_VMALLOC=y. If
the kasan_populate_vmalloc() gets failed for some reason it just
leaves the function, that will lead to waste of vmap space.

>  	spin_lock(&vmap_area_lock);
>  	insert_vmap_area(va, &vmap_area_root, &vmap_area_list);
>  	spin_unlock(&vmap_area_lock);
>
     ret = kasan_populate_vmalloc(addr, size);
     if (ret) {
         free_vmap_area(va);
         return ERR_PTR(-EBUSY);;
     }

> @@ -1169,8 +1174,9 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
>  		pr_warn("vmap allocation for size %lu failed: use vmalloc=<size> to increase size\n",
>  			size);
>  
> +out:
>  	kmem_cache_free(vmap_area_cachep, va);
> -	return ERR_PTR(-EBUSY);
> +	return ERR_PTR(ret);
>  }
>