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

[Mika Westerberg <mika.westerberg@linux.intel.com>]

On Wed, Nov 18, 2020 at 02:47:27PM +0100, Greg KH wrote:
> 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.

Indeed, I missed that.

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

Sure I'll do this in v2. Thanks!