Re: [PATCH 1/2] dmaengine: idxd: Remove improper idxd_free

[Yi Sun <yi.sun@intel.com>]

On 29.05.2025 18:07, Vinicius Costa Gomes wrote:
>Yi Sun <yi.sun@intel.com> writes:
>
>> On 29.05.2025 09:56, Vinicius Costa Gomes wrote:
>>>Hi,
>>>
>>>Yi Sun <yi.sun@intel.com> writes:
>>>
>>>> The put_device() call can be asynchronous cleanup via schedule_delayed_work
>>>> when CONFIG_DEBUG_KOBJECT_RELEASE is set. This results in a use-after-free
>>>> failure during module unloading if invoking idxd_free() immediately
>>>> afterward.
>>>>
>>>
>>>I think that adding the relevant part of the log would be helpful. (I am
>>>looking at either a similar, or this exact problem, so at least to me it
>>>would be helpful)
>>>
>> The issue is easily reproducible: unloading the module with 'modprobe -r idxd'
>> can trigger the call trace so long as a idxd_free() is called immediately
>> after the put_device().
>>
>
>Most probably the same issue I am looking at then.
>
Yes, and actually, the other patch (patch 2/2: "dmaengine: idxd: Fix refcount
underflow on module unload") addresses a similar issue which is triggered in
the same function and resulting in nearly identical call traces.

There are two separate code changes in idxd/init.c that can lead to a
'refcount_t: underflow; use-after-free' issue, both caused by incorrect
use of put_device().

Thanks
    --Sun, Yi