linux-kernel - Re: [PATCH v6] i3c: Add NULL pointer check in i3c_master_queue

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Message-ID: <Z+ReM0MYKuIz06De@lizhi-Precision-Tower-5810>
Date: Wed, 26 Mar 2025 16:06:11 -0400
From: Frank Li <Frank.li@....com>
To: Manjunatha Venkatesh <manjunatha.venkatesh@....com>
Cc: alexandre.belloni@...tlin.com, arnd@...db.de,
	gregkh@...uxfoundation.org, bbrezillon@...nel.org,
	linux-i3c@...ts.infradead.org, linux-kernel@...r.kernel.org,
	rvmanjumce@...il.com, stable@...r.kernel.org
Subject: Re: [PATCH v6] i3c: Add NULL pointer check in i3c_master_queue_ibi()

On Wed, Mar 26, 2025 at 06:00:46PM +0530, Manjunatha Venkatesh wrote:
> The I3C master driver may receive an IBI from a target device that has not
> been probed yet. In such cases, the master calls `i3c_master_queue_ibi()`
> to queue an IBI work task, leading to "Unable to handle kernel read from
> unreadable memory" and resulting in a kernel panic.
>
> Typical IBI handling flow:
> 1. The I3C master scans target devices and probes their respective drivers.
> 2. The target device driver calls `i3c_device_request_ibi()` to enable IBI
>    and assigns `dev->ibi = ibi`.
> 3. The I3C master receives an IBI from the target device and calls
>    `i3c_master_queue_ibi()` to queue the target device driver’s IBI
>    handler task.
>
> However, since target device events are asynchronous to the I3C probe
> sequence, step 3 may occur before step 2, causing `dev->ibi` to be `NULL`,
> leading to a kernel panic.
>
> Add a NULL pointer check in `i3c_master_queue_ibi()` to prevent accessing
> an uninitialized `dev->ibi`, ensuring stability.
>
> Fixes: 3a379bbcea0af ("i3c: Add core I3C infrastructure")
> Cc: stable@...r.kernel.org
> Link: https://lore.kernel.org/lkml/Z9gjGYudiYyl3bSe@lizhi-Precision-Tower-5810/
> Signed-off-by: Manjunatha Venkatesh <manjunatha.venkatesh@....com>
> ---

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

> Changes since v5:
>   - Updated subject and commit message  with some more information.
>
>  drivers/i3c/master.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/drivers/i3c/master.c b/drivers/i3c/master.c
> index d5dc4180afbc..c65006aa0684 100644
> --- a/drivers/i3c/master.c
> +++ b/drivers/i3c/master.c
> @@ -2561,6 +2561,9 @@ static void i3c_master_unregister_i3c_devs(struct i3c_master_controller *master)
>   */
>  void i3c_master_queue_ibi(struct i3c_dev_desc *dev, struct i3c_ibi_slot *slot)
>  {
> +	if (!dev->ibi || !slot)
> +		return;
> +
>  	atomic_inc(&dev->ibi->pending_ibis);
>  	queue_work(dev->ibi->wq, &slot->work);
>  }
> --
> 2.46.1
>