Re: [PATCH] mwifiex: Fix use-after-free bug due to race condition between main thread thread and timer thread

Zheng Hacker
2023-02-24T05:37:43Z

Hello Brain,

Thanks for your detailed review. Sorry we missed something. As you say, We are
lacking some consideration, the pointed race path could not happen. But after
diving deep into the code, we found another path.

Here is the possible path. In summary, if the execution of CPU1 is
stuck by fw_done,
the cpu0 will continue executing and free the adapter gets into
error-path. The cpu1
did not notice that and UAF happened.

If there is something else we didn't know, please feel free to let us know.

CPU0 CPU1
mwifiex_sdio_probe
mwifiex_add_card
mwifiex_init_hw_fw
request_firmware_nowait
mwifiex_fw_dpc
_mwifiex_fw_dpc
mwifiex_init_fw
mwifiex_main_process
mwifiex_exec_next_cmd
mwifiex_dnld_cmd_to_fw
mod_timer(&adapter->cmd_timer,..)
mwifiex_cmd_timeout_func

if_ops.card_reset(adapter)

mwifiex_sdio_card_reset
[*] stuck
in mwifiex_shutdown_sw
return 0 in mwifiex_dnld_cmd_to_fw
return 0 in mwifiex_exec_next_cmd
return 0 in mwifiex_main_process
return -EINPROGRESS in mwifiex_init_fw
get into error path, mwifiex_free_adapter
// free adapter
complete_all(fw_done);
[*]Go on
Use
adapter->fw_done

Best regards,
Zheng

Brian Norris <briannorris@chromium.org> 于2023年2月23日周四 05:20写道：
>
> On Wed, Feb 22, 2023 at 12:17:21PM +0800, Zheng Hacker wrote:
> > Could you please provide some advice about the fix?
>
> This entire driver's locking patterns (or lack
> thereof) need rewritten. This driver was probably written by someone
> that doesn't really understand concurrent programming. It really only
> works because the bulk of normal operation is sequentialized into the
> main loop (mwifiex_main_process()). Any time you get outside that,
> you're likely to find bugs.
>
> But now that I've looked a little further, I'm not confident you pointed
> out a real bug. How does mwifiex_sdio_card_reset_work() get past
> mwifiex_shutdown_sw() -> wait_for_completion(adapter->fw_done) ? That
> should ensure that _mwifiex_fw_dpc() is finished, and so we can't hit
> the race you point out.
>
> Note to self: ignore most "static analysis" reports of race conditions,
> unless they have thorough analysis or a runtime reproduction.
>
> Brian