Re: [PATCH RESEND] drivers:media:radio: Fix atomicity violation in fmc_send_cmd()

[Hans Verkuil <hverkuil-cisco@xs4all.nl>]

Hi Qiu-ji Chen,

On 30/10/2024 07:48, Qiu-ji Chen wrote:
> Atomicity violation occurs when the fmc_send_cmd() function is executed 
> simultaneously with the modification of the fmdev->resp_skb value. 
> Consider a scenario where, after passing the validity check within the 
> function, a non-null fmdev->resp_skb variable is assigned a null value. 
> This results in an invalid fmdev->resp_skb variable passing the validity 
> check. As seen in the later part of the function, skb = fmdev->resp_skb; 
> when the invalid fmdev->resp_skb passes the check, a null pointer 
> dereference error may occur at line 478, evt_hdr = (void *)skb->data;
> 
> To address this issue, it is recommended to include the validity check of 
> fmdev->resp_skb within the locked section of the function. This 
> modification ensures that the value of fmdev->resp_skb does not change 
> during the validation process, thereby maintaining its validity.
> 
> This possible bug is found by an experimental static analysis tool
> developed by our team. This tool analyzes the locking APIs
> to extract function pairs that can be concurrently executed, and then
> analyzes the instructions in the paired functions to identify possible
> concurrency bugs including data races and atomicity violations.

FYI, since this driver will be removed soon, I'm not taking this patch.

See this patch for the driver removal:

https://patchwork.linuxtv.org/project/linux-media/patch/20241028083030.26351-1-lukas.bulwahn@redhat.com/

Regards,

	Hans

> 
> Fixes: e8454ff7b9a4 ("[media] drivers:media:radio: wl128x: FM Driver Common sources")
> Cc: stable@vger.kernel.org
> Signed-off-by: Qiu-ji Chen <chenqiuji666@gmail.com>
> ---
>  drivers/media/radio/wl128x/fmdrv_common.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/media/radio/wl128x/fmdrv_common.c b/drivers/media/radio/wl128x/fmdrv_common.c
> index 3d36f323a8f8..4d032436691c 100644
> --- a/drivers/media/radio/wl128x/fmdrv_common.c
> +++ b/drivers/media/radio/wl128x/fmdrv_common.c
> @@ -466,11 +466,12 @@ int fmc_send_cmd(struct fmdev *fmdev, u8 fm_op, u16 type, void *payload,
>  			   jiffies_to_msecs(FM_DRV_TX_TIMEOUT) / 1000);
>  		return -ETIMEDOUT;
>  	}
> +	spin_lock_irqsave(&fmdev->resp_skb_lock, flags);
>  	if (!fmdev->resp_skb) {
> +		spin_unlock_irqrestore(&fmdev->resp_skb_lock, flags);
>  		fmerr("Response SKB is missing\n");
>  		return -EFAULT;
>  	}
> -	spin_lock_irqsave(&fmdev->resp_skb_lock, flags);
>  	skb = fmdev->resp_skb;
>  	fmdev->resp_skb = NULL;
>  	spin_unlock_irqrestore(&fmdev->resp_skb_lock, flags);