linux-kernel - [PATCH 2/2] coresight: etb10: Fix possible NULL ptr dereference in etb_enable

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Message-Id: <6f10c09e130ff241c728c40840f7aa67fdc1b737.1602074787.git.saiprakash.ranjan@codeaurora.org>
Date:   Wed,  7 Oct 2020 18:30:25 +0530
From:   Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
To:     Mathieu Poirier <mathieu.poirier@...aro.org>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Mike Leach <mike.leach@...aro.org>
Cc:     coresight@...ts.linaro.org, Stephen Boyd <swboyd@...omium.org>,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, denik@...gle.com,
        leo.yan@...aro.org, peterz@...radead.org,
        Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
Subject: [PATCH 2/2] coresight: etb10: Fix possible NULL ptr dereference in etb_enable_perf()

There was a report of NULL pointer dereference in ETF enable
path for perf CS mode with PID monitoring. It is almost 100%
reproducible when the process to monitor is something very
active such as chrome and with ETF as the sink, not ETR.

But code path shows that ETB has a similar path as ETF, so
there could be possible NULL pointer dereference crash in
ETB as well. Currently in a bid to find the pid, the owner
is dereferenced via task_pid_nr() call in etb_enable_perf()
and with owner being NULL, we can get a NULL pointer
dereference, so have a similar fix as ETF where we cache PID
in alloc_buffer() callback which is called as the part of
etm_setup_aux().

Fixes: 75d7dbd38824 ("coresight: etb10: Add support for CPU-wide trace scenarios")
Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
---
 drivers/hwtracing/coresight/coresight-etb10.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/hwtracing/coresight/coresight-etb10.c b/drivers/hwtracing/coresight/coresight-etb10.c
index 248cc82c838e..1b320ab581ca 100644
--- a/drivers/hwtracing/coresight/coresight-etb10.c
+++ b/drivers/hwtracing/coresight/coresight-etb10.c
@@ -176,6 +176,7 @@ static int etb_enable_perf(struct coresight_device *csdev, void *data)
 	unsigned long flags;
 	struct etb_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
 	struct perf_output_handle *handle = data;
+	struct cs_buffers *buf = etm_perf_sink_config(handle);
 
 	spin_lock_irqsave(&drvdata->spinlock, flags);
 
@@ -186,7 +187,7 @@ static int etb_enable_perf(struct coresight_device *csdev, void *data)
 	}
 
 	/* Get a handle on the pid of the process to monitor */
-	pid = task_pid_nr(handle->event->owner);
+	pid = buf->pid;
 
 	if (drvdata->pid != -1 && drvdata->pid != pid) {
 		ret = -EBUSY;
@@ -383,6 +384,7 @@ static void *etb_alloc_buffer(struct coresight_device *csdev,
 	if (!buf)
 		return NULL;
 
+	buf->pid = task_pid_nr(event->owner);
 	buf->snapshot = overwrite;
 	buf->nr_pages = nr_pages;
 	buf->data_pages = pages;
-- 
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