linux-kernel - Re: [PATCH] coresight: ETR: Fix ETR buffer use-after-free issue

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Message-ID: <5a95ad38-0b32-4889-a8fb-af7e79c2e862@oss.qualcomm.com>
Date: Mon, 20 Oct 2025 18:18:23 +0800
From: Jie Gan <jie.gan@....qualcomm.com>
To: Xiaoqi Zhuang <xiaoqi.zhuang@....qualcomm.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Mike Leach
 <mike.leach@...aro.org>,
        James Clark <james.clark@...aro.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc: coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH] coresight: ETR: Fix ETR buffer use-after-free issue



On 10/20/2025 5:06 PM, Xiaoqi Zhuang wrote:
> When ETR is enabled as CS_MODE_SYSFS, if the buffer size is changed
> and enabled again, currently sysfs_buf will point to the newly
> allocated memory(buf_new) and free the old memory(buf_old). But the
> etr_buf that is being used by the ETR remains pointed to buf_old, not
> updated to buf_new. In this case, it will result in a memory
> use-after-free issue.
> 
> Fix this by checking ETR's mode before updating and releasing buf_old,
> if the mode is CS_MODE_SYSFS, then skip updating and releasing it.
> 

I think we need a fix tag for the fix patch:
Fixes: de5461970b3e ("coresight: tmc: allocating memory when needed")

minor comment:
Since ETR is enabled, we can't switch the sysfs buffer, can we exit 
earlier by checking the CS_MODE to avoid allocating memory unnecessarily?

Besides,
Looks good to me.

Thanks,
Jie

> Signed-off-by: Xiaoqi Zhuang <xiaoqi.zhuang@....qualcomm.com>
> ---
>   drivers/hwtracing/coresight/coresight-tmc-etr.c | 7 +++++++
>   1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-tmc-etr.c b/drivers/hwtracing/coresight/coresight-tmc-etr.c
> index b07fcdb3fe1a..3e73cf2c38a3 100644
> --- a/drivers/hwtracing/coresight/coresight-tmc-etr.c
> +++ b/drivers/hwtracing/coresight/coresight-tmc-etr.c
> @@ -1268,6 +1268,13 @@ static struct etr_buf *tmc_etr_get_sysfs_buffer(struct coresight_device *csdev)
>   		goto out;
>   	}
>   
> +	/*
> +	 * Since this sink is already enabled, the existing buffer should not
> +	 * be released even if the buffer size has changed.
> +	 */
> +	if (coresight_get_mode(csdev) == CS_MODE_SYSFS)
> +		goto out;
> +
>   	/*
>   	 * If we don't have a buffer or it doesn't match the requested size,
>   	 * use the buffer allocated above. Otherwise reuse the existing buffer.
> 
> ---
> base-commit: 98ac9cc4b4452ed7e714eddc8c90ac4ae5da1a09
> change-id: 20251020-fix_etr_issue-02c706dbc899
> 
> Best regards,