Re: [PATCH v3 1/3] bus: mhi: ep: Add mhi_cntrl->flush_async() callback to flush the async read/write

[Frank Li]

On Wed, Jul 22, 2026 at 07:54:44AM +0200, Manivannan Sadhasivam via B4 Relay wrote:
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>
> From: Manivannan Sadhasivam <manivannan.sadhasivam@xxxxxxxxxxxxxxxx>
>
> MHI EP stack makes use of the MHI controller drivers like MHI EPF to do
> read/write to the host memory. And that driver is free to use mechanisms
> like DMA to offload the read/write operations.
>
> So if DMA is used for offload, then there is no guarantee that those DMA
> operations would be completed by the time mhi_ep_remove() gets called. This
> can lead to UAF (Use-After-Free) issues as the DMA callback can trigger
> xfer_cb() even after mhi_ep_remove() has returned.
>
> So to fix this issue, introduce the mhi_cntrl->flush_async() callback and
> call it in mhi_ep_remove() to drain all the in-flight async transfers
> before disconnecting the channels.
>
> The completion handlers keep triggering xfer_cb() as long as it is set. So
> flushing the transfers after notifying the client about the disconnect
> (-ENOTCONN) would still let a success callback slip through afterwards and
> lead to the same UAF. So disable the channels first to prevent new
> transfers, then flush the in-flight transfers so that their completions are
> delivered while xfer_cb() is still valid and only then notify the
> disconnect and clear xfer_cb().
>
> Cc: <stable+noautosel@xxxxxxxxxx> # Needs dmaengine driver fix as well
> Fixes: 2547beb00ddb ("bus: mhi: ep: Add support for async DMA read operation")
> Fixes: ee08acb58fe4 ("bus: mhi: ep: Add support for async DMA write operation")
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@xxxxxxxxxxxxxxxx>
> ---

Reviewed-by: Frank Li <Frank.Li@xxxxxxx>

>  drivers/bus/mhi/ep/main.c | 18 +++++++++++++++++-
>  include/linux/mhi_ep.h    |  2 ++
>  2 files changed, 19 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/bus/mhi/ep/main.c b/drivers/bus/mhi/ep/main.c
> index 0277e1ab1198..b94c571f01d8 100644
> --- a/drivers/bus/mhi/ep/main.c
> +++ b/drivers/bus/mhi/ep/main.c
> @@ -1612,6 +1612,7 @@ static void mhi_ep_remove(struct device *dev)
>  {
>         struct mhi_ep_device *mhi_dev = to_mhi_ep_device(dev);
>         struct mhi_ep_driver *mhi_drv = to_mhi_ep_driver(dev->driver);
> +       struct mhi_ep_cntrl *mhi_cntrl = mhi_dev->mhi_cntrl;
>         struct mhi_result result = {};
>         struct mhi_ep_chan *mhi_chan;
>         int dir;
> @@ -1620,6 +1621,22 @@ static void mhi_ep_remove(struct device *dev)
>         if (mhi_dev->dev_type == MHI_DEVICE_CONTROLLER)
>                 return;
>
> +       /* Disable the channels to prevent new transfers */
> +       for (dir = 0; dir < 2; dir++) {
> +               mhi_chan = dir ? mhi_dev->ul_chan : mhi_dev->dl_chan;
> +
> +               if (!mhi_chan)
> +                       continue;
> +
> +               mutex_lock(&mhi_chan->lock);
> +               mhi_chan->state = MHI_CH_STATE_DISABLED;
> +               mutex_unlock(&mhi_chan->lock);
> +       }
> +
> +       /* Flush in-flight transfers before notifying disconnect */
> +       if (mhi_cntrl->flush_async)
> +               mhi_cntrl->flush_async(mhi_cntrl);
> +
>         /* Disconnect the channels associated with the driver */
>         for (dir = 0; dir < 2; dir++) {
>                 mhi_chan = dir ? mhi_dev->ul_chan : mhi_dev->dl_chan;
> @@ -1635,7 +1652,6 @@ static void mhi_ep_remove(struct device *dev)
>                         mhi_chan->xfer_cb(mhi_chan->mhi_dev, &result);
>                 }
>
> -               mhi_chan->state = MHI_CH_STATE_DISABLED;
>                 mhi_chan->xfer_cb = NULL;
>                 mutex_unlock(&mhi_chan->lock);
>         }
> diff --git a/include/linux/mhi_ep.h b/include/linux/mhi_ep.h
> index 7b40fc8cbe77..f6383a57a872 100644
> --- a/include/linux/mhi_ep.h
> +++ b/include/linux/mhi_ep.h
> @@ -107,6 +107,7 @@ struct mhi_ep_buf_info {
>   * @write_sync: CB function for writing to host memory synchronously
>   * @read_async: CB function for reading from host memory asynchronously
>   * @write_async: CB function for writing to host memory asynchronously
> + * @flush_async: CB function for flushing asynchronous read/writes
>   * @mhi_state: MHI Endpoint state
>   * @max_chan: Maximum channels supported by the endpoint controller
>   * @mru: MRU (Maximum Receive Unit) value of the endpoint controller
> @@ -164,6 +165,7 @@ struct mhi_ep_cntrl {
>         int (*write_sync)(struct mhi_ep_cntrl *mhi_cntrl, struct mhi_ep_buf_info *buf_info);
>         int (*read_async)(struct mhi_ep_cntrl *mhi_cntrl, struct mhi_ep_buf_info *buf_info);
>         int (*write_async)(struct mhi_ep_cntrl *mhi_cntrl, struct mhi_ep_buf_info *buf_info);
> +       void (*flush_async)(struct mhi_ep_cntrl *mhi_cntrl);
>
>         enum mhi_state mhi_state;
>
>
> --
> 2.43.0
>
>