Re: [PATCH] memstick: rtsx_usb_ms: fix UAF

[Ulf Hansson <ulf.hansson@linaro.org>]

On Sun, 9 May 2021 at 23:54, Tong Zhang <ztong0001@gmail.com> wrote:
>
> This patch fixes the following issues:
> 1. memstick_free_host() will free the host, so the use of ms_dev(host) after
> it will be a problem. To fix this, move memstick_free_host() after when we
> are done with ms_dev(host).
> 2. if something bad happens in memstick_add_host() and we end up taking
> err_out in rtsx_usb_ms_drv_probe(), we'd better avoid running rtsx_usb_ms_drv_remove()

If the ->probe() function returns a negative error code, the driver
core will not invoke the corresponding ->remove() callback.

Looks like you may want to double check that ->probe() doesn't return
0, even in case of failure.

> 3. In rtsx_usb_ms_drv_remove(), pm need to be disabled before we remove
> and free host otherwise memstick_check will be called and UAF will
> happen.
>
> [   11.351173] BUG: KASAN: use-after-free in rtsx_usb_ms_drv_remove+0x94/0x140 [rtsx_usb_ms]
> [   11.357077]  rtsx_usb_ms_drv_remove+0x94/0x140 [rtsx_usb_ms]
> [   11.357376]  platform_remove+0x2a/0x50
> [   11.367531] Freed by task 298:
> [   11.368537]  kfree+0xa4/0x2a0
> [   11.368711]  device_release+0x51/0xe0
> [   11.368905]  kobject_put+0xa2/0x120
> [   11.369090]  rtsx_usb_ms_drv_remove+0x8c/0x140 [rtsx_usb_ms]
> [   11.369386]  platform_remove+0x2a/0x50
>
> [   12.038408] BUG: KASAN: use-after-free in __mutex_lock.isra.0+0x3ec/0x7c0
> [   12.045432]  mutex_lock+0xc9/0xd0
> [   12.046080]  memstick_check+0x6a/0x578 [memstick]
> [   12.046509]  process_one_work+0x46d/0x750
> [   12.052107] Freed by task 297:
> [   12.053115]  kfree+0xa4/0x2a0
> [   12.053272]  device_release+0x51/0xe0
> [   12.053463]  kobject_put+0xa2/0x120
> [   12.053647]  rtsx_usb_ms_drv_remove+0xc4/0x140 [rtsx_usb_ms]
> [   12.053939]  platform_remove+0x2a/0x50
>
> Signed-off-by: Tong Zhang <ztong0001@gmail.com>
> ---
>  drivers/memstick/host/rtsx_usb_ms.c | 13 +++++++------
>  1 file changed, 7 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/memstick/host/rtsx_usb_ms.c b/drivers/memstick/host/rtsx_usb_ms.c
> index 102dbb8080da..851643d007b7 100644
> --- a/drivers/memstick/host/rtsx_usb_ms.c
> +++ b/drivers/memstick/host/rtsx_usb_ms.c
> @@ -799,9 +799,10 @@ static int rtsx_usb_ms_drv_probe(struct platform_device *pdev)
>
>         return 0;
>  err_out:
> -       memstick_free_host(msh);
>         pm_runtime_disable(ms_dev(host));
>         pm_runtime_put_noidle(ms_dev(host));
> +       memstick_free_host(msh);
> +       platform_set_drvdata(pdev, NULL);
>         return err;
>  }
>
> @@ -811,6 +812,8 @@ static int rtsx_usb_ms_drv_remove(struct platform_device *pdev)
>         struct memstick_host *msh = host->msh;
>         int err;
>
> +       if (!host)
> +               return 0;

According to my comment above. You should not reach this point, unless
->probe() was successful and returned 0.

>         host->eject = true;
>         cancel_work_sync(&host->handle_req);
>
> @@ -828,9 +831,6 @@ static int rtsx_usb_ms_drv_remove(struct platform_device *pdev)
>         }
>         mutex_unlock(&host->host_mutex);
>
> -       memstick_remove_host(msh);
> -       memstick_free_host(msh);
> -
>         /* Balance possible unbalanced usage count
>          * e.g. unconditional module removal
>          */
> @@ -838,10 +838,11 @@ static int rtsx_usb_ms_drv_remove(struct platform_device *pdev)
>                 pm_runtime_put(ms_dev(host));
>
>         pm_runtime_disable(ms_dev(host));
> -       platform_set_drvdata(pdev, NULL);
> -
> +       memstick_remove_host(msh);
>         dev_dbg(ms_dev(host),
>                 ": Realtek USB Memstick controller has been removed\n");
> +       memstick_free_host(msh);
> +       platform_set_drvdata(pdev, NULL);
>
>         return 0;
>  }
> --
> 2.25.1
>

Besides the above, the change looks reasonable to me.

Kind regards
Uffe