[PATCHv2 4/4] coresight: tmc-etr: Fix possible NULL ptr dereference in get_perf_etr_buf_cpu_wide()

[Sai Prakash Ranjan]

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 but the ETR
may also be susceptible to this crash.

Currently in a bid to find the pid, the owner is dereferenced
via task_pid_nr() call in get_perf_etr_buf_cpu_wide() and
with owner being NULL and no proper validation of event->owner,
we can have a possible NULL pointer dereference, so add a check
to validate event->owner before dereferencing it to fix any
possible NULL pointer dereference crashes and also check for
kernel events.

Fixes: 3147da92a8a8 ("coresight: tmc-etr: Allocate and free ETR memory buffers for CPU-wide scenarios")
Suggested-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@xxxxxxxxxxxxxx>
---
 drivers/hwtracing/coresight/coresight-tmc-etr.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/hwtracing/coresight/coresight-tmc-etr.c b/drivers/hwtracing/coresight/coresight-tmc-etr.c
index 714f9e867e5f..305dfdd5345a 100644
--- a/drivers/hwtracing/coresight/coresight-tmc-etr.c
+++ b/drivers/hwtracing/coresight/coresight-tmc-etr.c
@@ -1381,6 +1381,10 @@ static void *tmc_alloc_etr_buffer(struct coresight_device *csdev,
 {
 	struct etr_perf_buffer *etr_perf;
 	struct tmc_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
+	struct task_struct *task = READ_ONCE(event->owner);
+
+	if (!task || is_kernel_event(event))
+		return NULL;
 
 	etr_perf = tmc_etr_setup_perf_buf(drvdata, event,
 					  nr_pages, pages, snapshot);
@@ -1389,7 +1393,7 @@ static void *tmc_alloc_etr_buffer(struct coresight_device *csdev,
 		return NULL;
 	}
 
-	etr_perf->pid = task_pid_nr(event->owner);
+	etr_perf->pid = task_pid_nr(task);
 	etr_perf->snapshot = snapshot;
 	etr_perf->nr_pages = nr_pages;
 	etr_perf->pages = pages;
-- 
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