[PATCH] intel_th: core: fix null pointer dereference in intel_th_irq

[David Arcari <darcari@redhat.com>]

In certain cases intel_th_irq can reference a null entry in
the th->thdev array.  This results in the splat shown below.
The problem is that intel_th_output_enable() can modify the
thdev[] array at the same time intel_th_irq is referencing
the same array.  This can be fixed by disabling interrupts
during the call to intel_th_output_enable().

BUG: kernel NULL pointer dereference, address: 0000000000000304
Oops: Oops: 0000 [#1] SMP NOPTI
RIP: 0010:intel_th_irq+0x26/0x70 [intel_th]
Call Trace:
 <IRQ>
 ? show_trace_log_lvl+0x1b0/0x2f0
 ? show_trace_log_lvl+0x1b0/0x2f0
 ? __handle_irq_event_percpu+0x4a/0x180
 ? __die_body.cold+0x8/0x12
 ? page_fault_oops+0x148/0x160
 ? exc_page_fault+0x73/0x160
 ? asm_exc_page_fault+0x26/0x30
 ? intel_th_irq+0x26/0x70 [intel_th]
 __handle_irq_event_percpu+0x4a/0x180
 handle_irq_event+0x38/0x80
handle_fasteoi_irq+0x78/0x200
__common_interrupt+0x3e/0x90
common_interrupt+0x80/0xa0
</IRQ>

Fixes: a753bfcfdb1f ("intel_th: Make the switch allocate its subdevices")
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: linux-kernel@vger.kernel.org
Cc: Jerry Hoemann <jerry.hoemann@hpe.com>
Signed-off-by: David Arcari <darcari@redhat.com>
---
 drivers/hwtracing/intel_th/core.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/drivers/hwtracing/intel_th/core.c b/drivers/hwtracing/intel_th/core.c
index 47d9e6c3bac0..c6f6153fcc88 100644
--- a/drivers/hwtracing/intel_th/core.c
+++ b/drivers/hwtracing/intel_th/core.c
@@ -715,7 +715,9 @@ intel_th_subdevice_alloc(struct intel_th *th,
 int intel_th_output_enable(struct intel_th *th, unsigned int otype)
 {
 	struct intel_th_device *thdev;
-	int src = 0, dst = 0;
+	int src = 0, dst = 0, ret = 0;
+
+	disable_irq(th->irq);
 
 	for (src = 0, dst = 0; dst <= th->num_thdevs; src++, dst++) {
 		for (; src < ARRAY_SIZE(intel_th_subdevices); src++) {
@@ -730,7 +732,7 @@ int intel_th_output_enable(struct intel_th *th, unsigned int otype)
 
 		/* no unallocated matching subdevices */
 		if (src == ARRAY_SIZE(intel_th_subdevices))
-			return -ENODEV;
+			goto nodev;
 
 		for (; dst < th->num_thdevs; dst++) {
 			if (th->thdev[dst]->type != INTEL_TH_OUTPUT)
@@ -750,16 +752,19 @@ int intel_th_output_enable(struct intel_th *th, unsigned int otype)
 			goto found;
 	}
 
+nodev:
+	enable_irq(th->irq);
 	return -ENODEV;
 
 found:
 	thdev = intel_th_subdevice_alloc(th, &intel_th_subdevices[src]);
 	if (IS_ERR(thdev))
-		return PTR_ERR(thdev);
-
-	th->thdev[th->num_thdevs++] = thdev;
+		ret = PTR_ERR(thdev);
+	else
+		th->thdev[th->num_thdevs++] = thdev;
 
-	return 0;
+	enable_irq(th->irq);
+	return ret;
 }
 EXPORT_SYMBOL_GPL(intel_th_output_enable);
 
-- 
2.50.1