Re: [PATCH] dm: introduce spinlocks to prevent concurrent usage and release of device_metadata and hash

[Mikulas Patocka <mpatocka@redhat.com>]

On Thu, 17 Jul 2025, Hou Tao wrote:

> Hi,
> 
> On 7/17/2025 10:07 PM, Li Lingfeng wrote:
> > There is a window between freeing md->ima.active_table.hash and setting
> > md->ima.active_table.hash to NULL in dm_ima_measure_on_device_resume().
> > If dm_ima_measure_on_device_remove() accesses md->ima.active_table.hash
> > concurrently during this window, it could lead to a double free or UAF,
> > as shown below:
> 
> The UAF is a problem. However, I think the order of
> dm_ima_measure_on_device_remove() and dm_ima_measure_on_device_resume is
> bigger problem. Is it possible to order these two invocations properly
> by using suspend_lock ?

That's a good point. The patch just papers over the problem. It will fix 
the UAF warning, but it won't fix the fact that 
dm_ima_measure_on_device_resume can race with 
dm_ima_measure_on_device_remove.

The real fix would be to make sure that dm_ima_measure_* calls are never 
called concurrently on the same table - we should use existing device 
mapper locks for that.

Mikukas