Re: [PATCH] binder: fix race that allows malicious free of live buffer

[Greg KH]

On Tue, Nov 06, 2018 at 03:55:32PM -0800, Todd Kjos wrote:
> Malicious code can attempt to free buffers using the
> BC_FREE_BUFFER ioctl to binder. There are protections
> against a user freeing a buffer while in use by the
> kernel, however there was a window where BC_FREE_BUFFER
> could be used to free a recently allocated buffer that
> was not completely initialized. This resulted in a
> use-after-free detected by KASAN with a malicious
> test program.
> 
> This window is closed by setting the buffer's
> allow_user_free attribute to 0 when the buffer
> is allocated or when the user has previously
> freed it instead of waiting for the caller
> to set it. The problem was that when the struct
> buffer was recycled, allow_user_free was stale
> and set to 1 allowing a free to go through.
> 
> Signed-off-by: Todd Kjos <tkjos@xxxxxxxxxx>
> Acked-by: Arve Hjønnevåg <arve@xxxxxxxxxxx>

No "stable" tag here?  Any idea how far back the stable backporting
should go, if any?

thanks,

greg k-h