Re: [PATCH] staging: greybus: timesync: validate platform state callback

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Hi Johan,
On Mon, Jan 23, 2017 at 04:28:08PM +0100, Johan Hovold wrote:
On Mon, Jan 23, 2017 at 02:22:44PM +0000, Rui Miguel Silva wrote:
When tearingdown timesync, and not in arche platform, the state platform
callback is not initialized. That will trigger the following NULL
dereferencing.
CallTrace:

 ? gb_timesync_platform_unlock_bus+0x11/0x20 [greybus]
 gb_timesync_teardown+0x85/0xc0 [greybus]
 gb_timesync_svc_remove+0xab/0x190 [greybus]
 gb_svc_del+0x29/0x110 [greybus]
 gb_hd_del+0x14/0x20 [greybus]
 ap_disconnect+0x24/0x60 [gb_es2]
 usb_unbind_interface+0x7a/0x2c0
 __device_release_driver+0x96/0x150
 device_release_driver+0x1e/0x30
 bus_remove_device+0xe7/0x130
 device_del+0x116/0x230
 usb_disable_device+0x97/0x1f0
 usb_disconnect+0x80/0x260
 hub_event+0x5ca/0x10e0
 process_one_work+0x126/0x3b0
 worker_thread+0x55/0x4c0
 ? process_one_work+0x3b0/0x3b0
 kthread+0xc4/0xe0
 ? kthread_park+0xb0/0xb0
 ret_from_fork+0x22/0x30

So, fix that by adding checks before use the callback.

Cc: <stable@xxxxxxxxxxxxxxx> # 4.9.x
Signed-off-by: Rui Miguel Silva <rmfrfs@xxxxxxxxx>
---
Greg,
This patch does not contain the "commit <sha> upstream" snippet since you
already removed the timesync code from the -next tree. So, It would never get
there. However this will affect the greybus users of 4.9.x.

This code is still in Linus tree and 4.10-rc so this is just a normal
fix even if this is no longer an issue in -next.


Yeah, but this code is not in staging-next anymore, It was mainly an
headsup for that, this patch will not apply to that tree.


 drivers/staging/greybus/timesync_platform.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/staging/greybus/timesync_platform.c b/drivers/staging/greybus/timesync_platform.c
index 113f3d6c4b3a..7d3ccc2bc98c 100644
--- a/drivers/staging/greybus/timesync_platform.c
+++ b/drivers/staging/greybus/timesync_platform.c
@@ -45,13 +45,18 @@ u32 gb_timesync_platform_get_clock_rate(void)

 int gb_timesync_platform_lock_bus(struct gb_timesync_svc *pdata)
 {
+	if (!arche_platform_change_state_cb)
+		return 0;
+
 	return arche_platform_change_state_cb(ARCHE_PLATFORM_STATE_TIME_SYNC,
 					      pdata);
 }

 void gb_timesync_platform_unlock_bus(void)
 {
-	arche_platform_change_state_cb(ARCHE_PLATFORM_STATE_ACTIVE, NULL);
+	if (arche_platform_change_state_cb)
+		arche_platform_change_state_cb(ARCHE_PLATFORM_STATE_ACTIVE,
+					       NULL);

I'd use the same pattern here:

	if (!arche_platform_change_state_cb)
		return;

	arche_platform_change_state_cb(ARCHE_PLATFORM_STATE_ACTIVE, NULL);


I also notice I forgot the Fixes: tag, so I will add your suggestion
to my v2.

Thanks Johan,
Cheers,
  Rui
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