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

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Message-Id: <20251020-fix_etr_issue-v1-1-902ab51770b4@oss.qualcomm.com>
Date: Mon, 20 Oct 2025 17:06:46 +0800
From: Xiaoqi Zhuang <xiaoqi.zhuang@....qualcomm.com>
To: 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,
        Xiaoqi Zhuang <xiaoqi.zhuang@....qualcomm.com>
Subject: [PATCH] coresight: ETR: Fix ETR buffer use-after-free issue

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.

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,
-- 
Xiaoqi Zhuang <xiaoqi.zhuang@....qualcomm.com>