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")
Cc: stable@vger.kernel.org
Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Link: https://lore.kernel.org/r/20201127175256.1092685-11-mathieu.poirier@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/hwtracing/coresight/coresight-etb10.c b/drivers/hwtracing/coresight/coresight-etb10.c
index 248cc82c838e722a8d60ecb6711327ffbd6e0bef..1b320ab581caf061357edc21afb3bffe020a8862 100644 (file)
--- 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;