Re: [PATCH] cxl/port: Hold port reference until decoder release

From: Ben Widawsky <ben.widawsky@intel.com>
To: Dan Williams <dan.j.williams@intel.com>
Cc: linux-cxl@vger.kernel.org
Subject: Re: [PATCH] cxl/port: Hold port reference until decoder release
Date: Thu, 17 Feb 2022 09:04:23 -0800	[thread overview]
Message-ID: <20220217170423.4x2j4aznppo5xc5i@intel.com> (raw)
In-Reply-To: <164505751190.4175768.13324905271463416712.stgit@dwillia2-desk3.amr.corp.intel.com>

On 22-02-16 16:25:11, Dan Williams wrote:
> KASAN + DEBUG_KOBJECT_RELEASE reports a potential use-after-free in
> cxl_decoder_release() where it goes to reference its parent, a cxl_port,
> to free its id back to port->decoder_ida.
> 
>  BUG: KASAN: use-after-free in to_cxl_port+0x18/0x90 [cxl_core]
>  Read of size 8 at addr ffff888119270908 by task kworker/35:2/379
> 
>  CPU: 35 PID: 379 Comm: kworker/35:2 Tainted: G           OE     5.17.0-rc2+ #198
>  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
>  Workqueue: events kobject_delayed_cleanup
>  Call Trace:
>   <TASK>
>   dump_stack_lvl+0x59/0x73
>   print_address_description.constprop.0+0x1f/0x150
>   ? to_cxl_port+0x18/0x90 [cxl_core]
>   kasan_report.cold+0x83/0xdf
>   ? to_cxl_port+0x18/0x90 [cxl_core]
>   to_cxl_port+0x18/0x90 [cxl_core]
>   cxl_decoder_release+0x2a/0x60 [cxl_core]
>   device_release+0x5f/0x100
>   kobject_cleanup+0x80/0x1c0
> 
> The device core only guarantees parent lifetime until all children are
> unregistered. If a child needs a parent to complete its ->release()
> callback that child needs to hold a reference to extend the lifetime of
> the parent.
> 
> Fixes: 40ba17afdfab ("cxl/acpi: Introduce cxl_decoder objects")
> Reported-by: Ben Widawsky <ben.widawsky@intel.com>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>

Tested-by: Ben Widawsky <ben.widawsky@intel.com>
Reviewed-by: Ben Widawsky <ben.widawsky@intel.com>