[PATCH 4.9 082/118] intel_th: Dont reference unassigned outputs

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>

commit 9ed3f22223c33347ed963e7c7019cf2956dd4e37 upstream.

When an output port driver is removed, also remove references to it from
any masters. Failing to do this causes a NULL ptr dereference when
configuring another output port:

> BUG: unable to handle kernel NULL pointer dereference at 000000000000000d
> RIP: 0010:master_attr_store+0x9d/0x160 [intel_th_gth]
> Call Trace:
> dev_attr_store+0x1b/0x30
> sysfs_kf_write+0x3c/0x50
> kernfs_fop_write+0x125/0x1a0
> __vfs_write+0x3a/0x190
> ? __vfs_write+0x5/0x190
> ? _cond_resched+0x1a/0x50
> ? rcu_all_qs+0x5/0xb0
> ? __vfs_write+0x5/0x190
> vfs_write+0xb8/0x1b0
> ksys_write+0x55/0xc0
> __x64_sys_write+0x1a/0x20
> do_syscall_64+0x5a/0x140
> entry_SYSCALL_64_after_hwframe+0x44/0xa9

Signed-off-by: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Fixes: b27a6a3f97b9 ("intel_th: Add Global Trace Hub driver")
CC: stable@xxxxxxxxxxxxxxx # v4.4+
Reported-by: Ammy Yi <ammy.yi@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/hwtracing/intel_th/gth.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/drivers/hwtracing/intel_th/gth.c
+++ b/drivers/hwtracing/intel_th/gth.c
@@ -599,11 +599,15 @@ static void intel_th_gth_unassign(struct
 {
 	struct gth_device *gth = dev_get_drvdata(&thdev->dev);
 	int port = othdev->output.port;
+	int master;
 
 	spin_lock(&gth->gth_lock);
 	othdev->output.port = -1;
 	othdev->output.active = false;
 	gth->output[port].output = NULL;
+	for (master = 0; master < TH_CONFIGURABLE_MASTERS; master++)
+		if (gth->master[master] == port)
+			gth->master[master] = -1;
 	spin_unlock(&gth->gth_lock);
 }