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

[Matthew Auld <matthew.auld@intel.com>]

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.

> 
>> v2:
>>   - Rebase
>>
>> Fixes: 2149ded63079 ("drm/xe: Fix use after free when client stats are captured")
>> Signed-off-by: Matthew Auld<matthew.auld@intel.com>
>> Cc: Matthew Brost<matthew.brost@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;
>>