Re: [PATCH] Input: synaptics-rmi4 - fix use after free (more completely) -- but not fully ;)

[Mathias Krause]

Hi Dan, Torsten,

On 22.02.24 09:53, Dan Carpenter wrote:
> From: Brad Spengler <spender@xxxxxxxxxxxxxx>
> 
> Grsecurity uses memory poisoning and detected a use after free in
> rmi_unregister_function().   A fix for this was merged into the
> grsecurity patchset.  I detected the user after free later using static
                                       ^^^^ use after free

> analysis and sent a partial fix as commit eb988e46da2e ("Input:
> synaptics-rmi4 - fix use after free in rmi_unregister_function()").
> However, my patch meant that the grsecurity patchset didn't apply cleanly
> and forced everyone to re-visit this issue.

Indeed. We even noticed that your patch was incomplete back then but
urgent matters kept us from following-up. Then came holidays and this
simply went forgotten :(

> 
> The bug is that we must not call device_del() until after calling
> irq_dispose_mapping().

Unfortunately, this is only half the truth. We investigated this further
and there's another bug that got introduced in commit 24d28e4f1271
("Input: synaptics-rmi4 - convert irq distribution to irq_domain"). The
IRQ domain has a UAF issue as well. I'll send the patch soon -- wanted
to do so this week, but, again, more urgent matters interrupted this.

> 
> Fixes: 24d28e4f1271 ("Input: synaptics-rmi4 - convert irq distribution to irq_domain")
> Reported-by: Torsten Hilbrich <torsten.hilbrich@xxxxxxxxxxx>
> Closes: https://lore.kernel.org/all/1932038e-2776-04ac-5fcd-b15bb3cd088d@xxxxxxxxxxx/
> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=215604
> Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
> ---
>  drivers/input/rmi4/rmi_bus.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/input/rmi4/rmi_bus.c b/drivers/input/rmi4/rmi_bus.c
> index 1b45b1d3077d..02acc81b9d3e 100644
> --- a/drivers/input/rmi4/rmi_bus.c
> +++ b/drivers/input/rmi4/rmi_bus.c
> @@ -275,12 +275,11 @@ void rmi_unregister_function(struct rmi_function *fn)
>  	rmi_dbg(RMI_DEBUG_CORE, &fn->dev, "Unregistering F%02X.\n",
>  			fn->fd.function_number);
>  
> -	device_del(&fn->dev);
> -	of_node_put(fn->dev.of_node);
> -
>  	for (i = 0; i < fn->num_of_irqs; i++)
>  		irq_dispose_mapping(fn->irq[i]);
>  
> +	device_del(&fn->dev);
> +	of_node_put(fn->dev.of_node);
>  	put_device(&fn->dev);
>  }
>  

Acked-by: Mathias Krause <minipli@xxxxxxxxxxxxxx>