Re: [PATCH] crypto: qat - fix use-after-free during concurrent device start and removal

[Giovanni Cabiddu]

Hi Mingyu,

Thanks for your patches.

The ioctl interface exposed by the QAT driver is not part of any public
uAPI header and has no known users. I just sent a series that removes it
entirely [1], which also eliminates this issue.

[1] https://lore.kernel.org/all/20260508091912.206913-1-giovanni.cabiddu@xxxxxxxxx/

Regards,

-- 
Giovanni

On Mon, May 04, 2026 at 03:51:20AM +0100, w15303746062@xxxxxxx wrote:
> From: Mingyu Wang <25181214217@xxxxxxxxxxxxxxxxx>
> 
> A Use-After-Free (UAF) vulnerability was identified in the QAT driver's ioctl path. When handling commands like IOCTL_START_ACCEL_DEV, `adf_ctl_ioctl_dev_start()` retrieves the acceleration device using `adf_devmgr_get_dev_by_id()`.
> 
> Previously, this lookup function iterated over the `accel_table` under the `table_lock`. However, once the target device was found, the lock was dropped and a bare pointer was returned without incrementing the device's reference count.
> 
> This creates a critical race condition. If a concurrent thread removes the device (e.g., via device stop operations or PCIe hotplug) by calling `adf_devmgr_rm_dev()`, the device is removed from the list and its memory is subsequently freed. When the original ioctl thread resumes and attempts to acquire `accel_dev->state_lock` inside `adf_dev_up()`, it triggers a KASAN slab-out-of-bounds panic.
> 
> Fix this by properly leveraging the existing `ref_count`. Increment the device's `ref_count` via `atomic_inc()` inside `adf_devmgr_get_dev_by_id()` while the `table_lock` is still held. All callers of `adf_devmgr_get_dev_by_id()` are then updated to safely release this reference using `atomic_dec(&accel_dev->ref_count)` once they are done interacting with the device.
> 
> Signed-off-by: Mingyu Wang <25181214217@xxxxxxxxxxxxxxxxx>
> ---
>  drivers/crypto/intel/qat/qat_common/adf_ctl_drv.c | 10 ++++++++++
>  drivers/crypto/intel/qat/qat_common/adf_dev_mgr.c | 12 ++++++++++--
>  2 files changed, 20 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/crypto/intel/qat/qat_common/adf_ctl_drv.c b/drivers/crypto/intel/qat/qat_common/adf_ctl_drv.c
> index c2e6f0cb7480..4924b2bbb412 100644
> --- a/drivers/crypto/intel/qat/qat_common/adf_ctl_drv.c
> +++ b/drivers/crypto/intel/qat/qat_common/adf_ctl_drv.c
> @@ -201,6 +201,9 @@ static int adf_ctl_ioctl_dev_config(struct file *fp, unsigned int cmd,
>  	}
>  	set_bit(ADF_STATUS_CONFIGURED, &accel_dev->status);
>  out:
> +	/* Release the reference acquired by adf_devmgr_get_dev_by_id() */
> +	if (accel_dev)
> +		atomic_dec(&accel_dev->ref_count);
>  	kfree(ctl_data);
>  	return ret;
>  }
> @@ -310,6 +313,9 @@ static int adf_ctl_ioctl_dev_start(struct file *fp, unsigned int cmd,
>  		adf_dev_down(accel_dev);
>  	}
>  out:
> +	/* Release the reference acquired by adf_devmgr_get_dev_by_id() */
> +	if (accel_dev)
> +		atomic_dec(&accel_dev->ref_count);
>  	kfree(ctl_data);
>  	return ret;
>  }
> @@ -360,8 +366,12 @@ static int adf_ctl_ioctl_get_status(struct file *fp, unsigned int cmd,
>  	if (copy_to_user((void __user *)arg, &dev_info,
>  			 sizeof(struct adf_dev_status_info))) {
>  		dev_err(&GET_DEV(accel_dev), "failed to copy status.\n");
> +		atomic_dec(&accel_dev->ref_count);
>  		return -EFAULT;
>  	}
> +	
> +	/* Release the reference acquired by adf_devmgr_get_dev_by_id() */
> +	atomic_dec(&accel_dev->ref_count);
>  	return 0;
>  }
>  
> diff --git a/drivers/crypto/intel/qat/qat_common/adf_dev_mgr.c b/drivers/crypto/intel/qat/qat_common/adf_dev_mgr.c
> index e050de16ab5d..321bea3cefce 100644
> --- a/drivers/crypto/intel/qat/qat_common/adf_dev_mgr.c
> +++ b/drivers/crypto/intel/qat/qat_common/adf_dev_mgr.c
> @@ -320,6 +320,8 @@ struct adf_accel_dev *adf_devmgr_get_dev_by_id(u32 id)
>  		struct adf_accel_dev *ptr =
>  				list_entry(itr, struct adf_accel_dev, list);
>  		if (ptr->accel_id == id) {
> +			/* Increment ref_count to prevent UAF during concurrent removal */
> +			atomic_inc(&ptr->ref_count);
>  			mutex_unlock(&table_lock);
>  			return ptr;
>  		}
> @@ -331,11 +333,17 @@ struct adf_accel_dev *adf_devmgr_get_dev_by_id(u32 id)
>  
>  int adf_devmgr_verify_id(u32 id)
>  {
> +	struct adf_accel_dev *accel_dev;
> +	
>  	if (id == ADF_CFG_ALL_DEVICES)
>  		return 0;
>  
> -	if (adf_devmgr_get_dev_by_id(id))
> -		return 0;
> +	accel_dev = adf_devmgr_get_dev_by_id(id);
> +	if (accel_dev) {
> +		/* Release the reference immediately as we only verify existence */
> +		atomic_dec(&accel_dev->ref_count);
> + 		return 0;
> +	}
>  
>  	return -ENODEV;
>  }
> -- 
> 2.34.1
>