Re: use-after-free in srpt_enable_tpg()

[Jason Gunthorpe]

On Mon, Jul 04, 2022 at 09:34:07PM -0700, Bart Van Assche wrote:
> On 7/3/22 17:11, Hillf Danton wrote:
> > On Sun, 3 Jul 2022 07:55:05 -0700 Bart Van Assche wrote:
> > > However, I'm not sure that would make a
> > > significant difference since there is a similar while-loop in one of the
> > > callers of srpt_remove_one() (disable_device() in the RDMA core).
> > 
> > Hehe... feel free to shed light on how the loop in RDMA core is currently
> > making the loop in srpt more prone to uaf?
> 
> In my email I was referring to the following code in disable_device():
> 
>        wait_for_completion(&device->unreg_completion);
> 
> I think that code shows that device removal by the RDMA core is synchronous
> in nature. Even if the ib_srpt source code would be modified such that the
> objects referred by that code live longer, the wait loop in disable_device()
> would wait for the ib_device reference counts to drop to zero.

That is not really the "ib_device" reference count it is the
"registration" reference count.

IB has a system where drivers/ulp can create critical regions where
the ib device must be registered using the ib_device_try_get()/put
calls. "Must be registered" is useful in a number of places but should
not be held for a long period.

This is distinct from the normal struct device refcount that simply
keeps the ib_device memory alive.

Jason