Re: [PATCH] thunderbolt: Fix use-after-free in remove_unplugged_switch()

[Greg KH <gregkh@linuxfoundation.org>]

On Wed, Nov 18, 2020 at 04:37:45PM +0300, Mika Westerberg wrote:
> Paulian reported a crash that happens when a dock is unplugged during
> hibernation:
> 
> [78436.228217] thunderbolt 0-1: device disconnected
> [78436.228365] BUG: kernel NULL pointer dereference, address: 00000000000001e0
> ...
> [78436.228397] RIP: 0010:icm_free_unplugged_children+0x109/0x1a0
> ...
> [78436.228432] Call Trace:
> [78436.228439]  icm_rescan_work+0x24/0x30
> [78436.228444]  process_one_work+0x1a3/0x3a0
> [78436.228449]  worker_thread+0x30/0x370
> [78436.228454]  ? process_one_work+0x3a0/0x3a0
> [78436.228457]  kthread+0x13d/0x160
> [78436.228461]  ? kthread_park+0x90/0x90
> [78436.228465]  ret_from_fork+0x1f/0x30
> 
> This happens because remove_unplugged_switch() calls tb_switch_remove()
> that releases the memory pointed by sw so the following lines reference
> to a memory that might be released already.
> 
> Fix this by saving pointer to the parent device before calling
> tb_switch_remove().
> 
> Reported-by: Paulian Bogdan Marinca <paulian@marinca.net>
> Fixes: 4f7c2e0d8765 ("thunderbolt: Make sure device runtime resume completes before taking domain lock")
> Cc: stable@vger.kernel.org
> Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
> ---
>  drivers/thunderbolt/icm.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/thunderbolt/icm.c b/drivers/thunderbolt/icm.c
> index b51fc3f62b1f..05323c442b56 100644
> --- a/drivers/thunderbolt/icm.c
> +++ b/drivers/thunderbolt/icm.c
> @@ -1976,7 +1976,9 @@ static int complete_rpm(struct device *dev, void *data)
>  
>  static void remove_unplugged_switch(struct tb_switch *sw)
>  {
> -	pm_runtime_get_sync(sw->dev.parent);
> +	struct device *parent = sw->dev.parent;
> +
> +	pm_runtime_get_sync(parent);

If you are saving a pointer to a structure, shouldn't you increment the
reference count?

	struct device *parent = get_device(sw->dev.parent);

Then you know it is valid when you use it later on.

Just remember to call put_device() when you are done.

thanks,

greg k-h