Re: [PATCH] uprobes: use vm_special_mapping close() functionality

[Oleg Nesterov <oleg@redhat.com>]

On 09/03, Sven Schnelle wrote:
>
> [   44.505448] ==================================================================                                                                      20:37:27 [3421/145075]
> [   44.505455] BUG: KASAN: slab-use-after-free in special_mapping_close+0x9c/0xc8
> [   44.505471] Read of size 8 at addr 00000000868dac48 by task sh/1384
> [   44.505479]
> [   44.505486] CPU: 51 UID: 0 PID: 1384 Comm: sh Not tainted 6.11.0-rc6-next-20240902-dirty #1496
> [   44.505503] Hardware name: IBM 3931 A01 704 (z/VM 7.3.0)
> [   44.505508] Call Trace:
> [   44.505511]  [<000b0324d2f78080>] dump_stack_lvl+0xd0/0x108
> [   44.505521]  [<000b0324d2f5435c>] print_address_description.constprop.0+0x34/0x2e0
> [   44.505529]  [<000b0324d2f5464c>] print_report+0x44/0x138
> [   44.505536]  [<000b0324d1383192>] kasan_report+0xc2/0x140
> [   44.505543]  [<000b0324d2f52904>] special_mapping_close+0x9c/0xc8
                                       ^^^^^^^^^^^^^^^^^^^^^
Caused by

	[PATCH v2 1/4] mm: Add optional close() to struct vm_special_mapping
	https://lore.kernel.org/all/20240812082605.743814-1-mpe@ellerman.id.au/

?

> +static void uprobe_clear_state(const struct vm_special_mapping *sm, struct vm_area_struct *vma)
> +{
> +	struct xol_area *area = container_of(vma->vm_private_data, struct xol_area, xol_mapping);
> +
> +	mutex_lock(&delayed_uprobe_lock);
> +	delayed_uprobe_remove(NULL, vma->vm_mm);
> +	mutex_unlock(&delayed_uprobe_lock);
> +
> +	if (!area)
> +		return;
> +
> +	put_page(area->pages[0]);
> +	kfree(area->bitmap);
> +	kfree(area);
> +}
> +
>  static struct xol_area *__create_xol_area(unsigned long vaddr)
>  {
>  	struct mm_struct *mm = current->mm;
> @@ -1481,6 +1500,7 @@ static struct xol_area *__create_xol_area(unsigned long vaddr)
>
>  	area->xol_mapping.name = "[uprobes]";
>  	area->xol_mapping.fault = NULL;
> +	area->xol_mapping.close = uprobe_clear_state;

LGTM.

but with or without this fix __create_xol_area() also needs

	area->xol_mapping.mremap = NULL;

?

And in the longer term I think we should probably add a single instance
of "struct vm_special_mapping uprobe_special_mapping with ->fault != NULL
but this is another issue.

Oleg.