Re: [PATCH v4 5/7] binder: check vma->vm_start in binder_vma_close()

[Alice Ryhl <aliceryhl@google.com>]

On Tue, Sep 01, 2026 at 08:52:45PM +0000, Carlos Llamas wrote:
> Certain operations like a failed mremap() might trigger vm_ops->close()
> on temporary mappings. To avoid tearing-down the main binder mapping on
> these, let's verify that the VMA matches the expected starting address.
> 
> Cc: stable@vger.kernel.org
> Fixes: 457b9a6f09f0 ("Staging: android: add binder driver")
> Reported-by: Sashiko <sashiko-bot@kernel.org>
> Closes: https://sashiko.dev/#/patchset/20260831224145.169403-1-cmllamas@google.com?part=1
> Signed-off-by: Carlos Llamas <cmllamas@google.com>
> ---
>  drivers/android/binder.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/android/binder.c b/drivers/android/binder.c
> index 185128577829..3d359490436e 100644
> --- a/drivers/android/binder.c
> +++ b/drivers/android/binder.c
> @@ -6018,6 +6018,9 @@ static void binder_vma_close(struct vm_area_struct *vma)
>  {
>  	struct binder_proc *proc = vma->vm_private_data;
>  
> +	if (vma->vm_start != proc->alloc.vm_start)
> +		return;

So .. this does work in the case of mremap, but how about instead doing
this?

static int binder_mremap(struct vm_area_struct *vma)
{
	vma->vm_private_data = NULL;
	return -EINVAL;
}

and then check for NULL in binder_vma_close() instead? I think that
logic would be a bit easier to understand.

Alice