Re: [PATCH] memstick: rtsx_usb_ms: fix UAF

[Tong Zhang]

On Tue, May 11, 2021 at 3:40 AM Ulf Hansson <ulf.hansson@xxxxxxxxxx> wrote:
>
> On Sun, 9 May 2021 at 23:54, Tong Zhang <ztong0001@xxxxxxxxx> 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@xxxxxxxxx>
> > ---
> >  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
Thanks Uffe!
I modified the patch as suggested and sent as v2.
Best,
- Tong