[PATCH v2 2/2] drm/xe/queue: move xa_alloc to prevent UAF

[Nirmoy Das]

On 9/25/2024 11:51 AM, Matthew Auld wrote:
> On 25/09/2024 10:33, Nirmoy Das wrote:
>>
>> On 9/25/2024 9:14 AM, Matthew Auld wrote:
>>> Evil user can guess the next id of the queue before the ioctl completes
>>> and then call queue destroy ioctl to trigger UAF since create ioctl is
>>> still referencing the same queue. Move the xa_alloc all the way to the end
>>> to prevent this.
>>
>> The commit message doesn't match the diff, xa_alloc already happening at the end here.
>
> It's not at the end. It is dereferencing the q to set xef after the xa_alloc, but that needs to happen before it is visible to userspace.


Ah I see, that make sense.

I think now  we have to undo xe_file_get() if xe_alloc fails.


Regards,

Nirmoy

>
>>
>>> v2:
>>>   - Rebase
>>>
>>> Fixes: 2149ded63079 ("drm/xe: Fix use after free when client stats are captured")
>>> Signed-off-by: Matthew Auld<matthew.auld at intel.com>
>>> Cc: Matthew Brost<matthew.brost at intel.com>
>>> ---
>>>   drivers/gpu/drm/xe/xe_exec_queue.c | 4 +++-
>>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/gpu/drm/xe/xe_exec_queue.c b/drivers/gpu/drm/xe/xe_exec_queue.c
>>> index 7743ebdcbf4b..d098d2dd1b2d 100644
>>> --- a/drivers/gpu/drm/xe/xe_exec_queue.c
>>> +++ b/drivers/gpu/drm/xe/xe_exec_queue.c
>>> @@ -635,12 +635,14 @@ int xe_exec_queue_create_ioctl(struct drm_device *dev, void *data,
>>>           }
>>>       }
>>>   +    q->xef = xe_file_get(xef);
>>> +
>>> +    /* user id alloc must always be last in ioctl to prevent UAF */
>>>       err = xa_alloc(&xef->exec_queue.xa, &id, q, xa_limit_32b, GFP_KERNEL);
>>>       if (err)
>>>           goto kill_exec_queue;
>>>         args->exec_queue_id = id;
>>> -    q->xef = xe_file_get(xef);
>>>         return 0;
>>>