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Subject[PATCH] coresight: access conn->child_name only if it's initialised
Date
If the addition of the coresight devices get deferred, then there's a
window before child_name is populated by of_get_coresight_platform_data
from the respective component driver's probe and the attempted to access
the same from coresight_orphan_match resulting in kernel NULL pointer
dereference as below:

Unable to handle kernel NULL pointer dereference at virtual address 0x0
Internal error: Oops: 96000004 [#1] PREEMPT SMP
Modules linked in:
CPU: 0 PID: 1038 Comm: kworker/0:1 Not tainted 4.7.0-rc3 #124
Hardware name: ARM Juno development board (r2) (DT)
Workqueue: events amba_deferred_retry_func
PC is at strcmp+0x1c/0x160
LR is at coresight_orphan_match+0x7c/0xd0
Call trace:
strcmp+0x1c/0x160
bus_for_each_dev+0x60/0xa0
coresight_register+0x264/0x2e0
tmc_probe+0x130/0x310
amba_probe+0xd4/0x1c8
driver_probe_device+0x22c/0x418
__device_attach_driver+0xbc/0x158
bus_for_each_drv+0x58/0x98
__device_attach+0xc4/0x160
device_initial_probe+0x10/0x18
bus_probe_device+0x94/0xa0
device_add+0x344/0x580
amba_device_try_add+0x194/0x238
amba_deferred_retry_func+0x48/0xd0
process_one_work+0x118/0x378
worker_thread+0x48/0x498
kthread+0xd0/0xe8
ret_from_fork+0x10/0x40

This patch adds a check for non-NULL conn->child_name before accessing
the same.

Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
---
drivers/hwtracing/coresight/coresight.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/hwtracing/coresight/coresight.c b/drivers/hwtracing/coresight/coresight.c
index 5443d03a1eec..12ca4cd97f5b 100644
--- a/drivers/hwtracing/coresight/coresight.c
+++ b/drivers/hwtracing/coresight/coresight.c
@@ -722,7 +722,8 @@ static int coresight_orphan_match(struct device *dev, void *data)
/* We have found at least one orphan connection */
if (conn->child_dev == NULL) {
/* Does it match this newly added device? */
- if (!strcmp(dev_name(&csdev->dev), conn->child_name)) {
+ if (conn->child_name &&
+ !strcmp(dev_name(&csdev->dev), conn->child_name)) {
conn->child_dev = csdev;
} else {
/* This component still has an orphan */
--
2.7.4
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