Re: [RFC PATCH] spi: fix use-after-free of the add_lock mutex

[Andy Shevchenko <andy.shevchenko@xxxxxxxxx>]

On Wed, Nov 10, 2021 at 6:09 PM Michael Walle <michael@xxxxxxxx> wrote:
>
> Commit 6098475d4cb4 ("spi: Fix deadlock when adding SPI controllers on
> SPI buses") introduced a per-controller mutex. But mutex_unlock() of
> said lock is called after the controller is already freed:
>
>   spi_unregister_controller(ctlr)
>    -> put_device(&ctlr->dev)
>     -> spi_controller_release(dev)
>   mutex_unlock(&ctrl->add_lock)
>
> Move the put_device() after the mutex_unlock().

I have a déjà-vu feeling about this code (Cc Lukas).

>
> Fixes: 6098475d4cb4 ("spi: Fix deadlock when adding SPI controllers on SPI buses")
> Signed-off-by: Michael Walle <michael@xxxxxxxx>
> ---
> I'm not sure if this is the correct fix. I don't know if the put_device()
> will have to be protected by the add_lock (remember before, the add_lock
> was a global lock).
>
> For reference, the kernel oops is:
> [   20.242505] Unable to handle kernel paging request at virtual address 0042a2203dc65260
> [   20.250468] Mem abort info:
> [   20.253270]   ESR = 0x96000044
> [   20.256332]   EC = 0x25: DABT (current EL), IL = 32 bits
> [   20.261662]   SET = 0, FnV = 0
> [   20.264723]   EA = 0, S1PTW = 0
> [   20.267869]   FSC = 0x04: level 0 translation fault
> [   20.272764] Data abort info:
> [   20.275646]   ISV = 0, ISS = 0x00000044
> [   20.279494]   CM = 0, WnR = 1
> [   20.282469] [0042a2203dc65260] address between user and kernel address ranges
> [   20.289632] Internal error: Oops: 96000044 [#1] SMP
> [   20.294525] Modules linked in:
> [   20.297586] CPU: 1 PID: 1546 Comm: init Not tainted 5.15.0-next-20211109+ #1307
> [   20.304919] Hardware name: Kontron KBox A-230-LS (DT)
> [   20.309983] pstate: 80000005 (Nzcv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
> [   20.316968] pc : queued_spin_lock_slowpath+0x1a8/0x3a0
> [   20.322127] lr : __mutex_unlock_slowpath.constprop.0+0x180/0x190
> [   20.328156] sp : ffff800013c23b80
> [   20.331475] x29: ffff800013c23b80 x28: ffff002003941040 x27: 0000000000000000
> [   20.338639] x26: ffff002000e49c90 x25: ffff80001167de48 x24: ffff800011f55578
> [   20.345802] x23: ffff002002b1d350 x22: 0000000000000002 x21: 0000000000000001
> [   20.352964] x20: ffff800013c23bb8 x19: ffff002002b1d350 x18: 00000000fffffffb
> [   20.360126] x17: 0000000000000001 x16: 0000000000000001 x15: 0000000000000020
> [   20.367288] x14: 0000000000000001 x13: 0000000000000000 x12: ffff002002c27938
> [   20.374450] x11: ffff002002c27908 x10: 0000000000000000 x9 : 0000000000080000
> [   20.381612] x8 : 0000000000000000 x7 : ffff00207f7b7a00 x6 : ffff8000119d1a00
> [   20.388774] x5 : ffff00207f7b7a00 x4 : 504322202c293830 x3 : ffff002002b1d358
> [   20.395936] x2 : ffff8000119d1a30 x1 : ffff8000119d1a30 x0 : ffff00207f7b7a08
> [   20.403098] Call trace:
> [   20.405546]  queued_spin_lock_slowpath+0x1a8/0x3a0
> [   20.410352]  mutex_unlock+0x5c/0x70
> [   20.413849]  spi_unregister_controller+0xf0/0x170
> [   20.418568]  dspi_remove+0x28/0xb0
> [   20.421978]  dspi_shutdown+0x1c/0x30
> [   20.425561]  platform_shutdown+0x30/0x40
> [   20.429495]  device_shutdown+0x14c/0x420
> [   20.433427]  __do_sys_reboot+0x214/0x29c
> [   20.437361]  __arm64_sys_reboot+0x30/0x40
> [   20.441380]  invoke_syscall+0x50/0x120
> [   20.445140]  el0_svc_common.constprop.0+0x58/0x190
> [   20.449944]  do_el0_svc+0x30/0x94
> [   20.453267]  el0_svc+0x20/0x90
> [   20.456327]  el0t_64_sync_handler+0x1a4/0x1b0
> [   20.460694]  el0t_64_sync+0x1a0/0x1a4
> [   20.464368] Code: 910020e0 8b0200c2 f861d884 aa0203e1 (f8246827)
> [   20.470479] ---[ end trace 9ee0c21f9e4bc5d5 ]---
> [   21.475251] Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000000
> [   21.482940] Kernel Offset: disabled
> [   21.486433] CPU features: 0x2,000001c2,40000846
> [   21.490976] Memory Limit: none
> [   21.494036] ---[ end Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000000 ]---
>
>  drivers/spi/spi.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
> index b23e675953e1..fdd530b150a7 100644
> --- a/drivers/spi/spi.c
> +++ b/drivers/spi/spi.c
> @@ -3099,12 +3099,6 @@ void spi_unregister_controller(struct spi_controller *ctlr)
>
>         device_del(&ctlr->dev);
>
> -       /* Release the last reference on the controller if its driver
> -        * has not yet been converted to devm_spi_alloc_master/slave().
> -        */
> -       if (!ctlr->devm_allocated)
> -               put_device(&ctlr->dev);
> -
>         /* free bus id */
>         mutex_lock(&board_lock);
>         if (found == ctlr)
> @@ -3113,6 +3107,12 @@ void spi_unregister_controller(struct spi_controller *ctlr)
>
>         if (IS_ENABLED(CONFIG_SPI_DYNAMIC))
>                 mutex_unlock(&ctlr->add_lock);
> +
> +       /* Release the last reference on the controller if its driver
> +        * has not yet been converted to devm_spi_alloc_master/slave().
> +        */
> +       if (!ctlr->devm_allocated)
> +               put_device(&ctlr->dev);
>  }
>  EXPORT_SYMBOL_GPL(spi_unregister_controller);
>
> --
> 2.30.2
>


-- 
With Best Regards,
Andy Shevchenko