Patch "iio: adis_lib: Initialize trigger before requesting interrupt" has been added to the 4.14-stable tree

This is a note to let you know that I've just added the patch titled

iio: adis_lib: Initialize trigger before requesting interrupt

to the 4.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
iio-adis_lib-initialize-trigger-before-requesting-interrupt.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Lars-Peter Clausen <[email protected]>
Date: Wed, 14 Feb 2018 15:43:00 +0100
Subject: iio: adis_lib: Initialize trigger before requesting interrupt

From: Lars-Peter Clausen <[email protected]>

commit f027e0b3a774e10302207e91d304bbf99e3a8b36 upstream.

The adis_probe_trigger() creates a new IIO trigger and requests an interrupt associated with the trigger. The interrupt uses the generic iio_trigger_generic_data_rdy_poll() function as its interrupt handler.

Currently the driver initializes some fields of the trigger structure after the interrupt has been requested. But an interrupt can fire as soon as it has been requested. This opens up a race condition.

iio_trigger_generic_data_rdy_poll() will access the trigger data structure and dereference the ops field. If the ops field is not yet initialized this will result in a NULL pointer deref.

It is not expected that the device generates an interrupt at this point, so typically this issue did not surface unless e.g. due to a hardware misconfiguration (wrong interrupt number, wrong polarity, etc.).

But some newer devices from the ADIS family start to generate periodic interrupts in their power-on reset configuration and unfortunately the interrupt can not be masked in the device. This makes the race condition much more visible and the following crash has been observed occasionally when booting a system using the ADIS16460.

	Unable to handle kernel NULL pointer dereference at virtual address 00000008
	pgd = c0004000
	[00000008] *pgd=00000000
	Internal error: Oops: 5 [#1] PREEMPT SMP ARM
	Modules linked in:
	CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.9.0-04126-gf9739f0-dirty #257
	Hardware name: Xilinx Zynq Platform
	task: ef04f640 task.stack: ef050000
	PC is at iio_trigger_notify_done+0x30/0x68
	LR is at iio_trigger_generic_data_rdy_poll+0x18/0x20
	pc : [<c042d868>]    lr : [<c042d924>]    psr: 60000193
	sp : ef051bb8  ip : 00000000  fp : ef106400
	r10: c081d80a  r9 : ef3bfa00  r8 : 00000087
	r7 : ef051bec  r6 : 00000000  r5 : ef3bfa00  r4 : ee92ab00
	r3 : 00000000  r2 : 00000000  r1 : 00000000  r0 : ee97e400
	Flags: nZCv  IRQs off  FIQs on  Mode SVC_32  ISA ARM  Segment none
	Control: 18c5387d  Table: 0000404a  DAC: 00000051
	Process swapper/0 (pid: 1, stack limit = 0xef050210)
	[<c042d868>] (iio_trigger_notify_done) from [<c0065b10>] (__handle_irq_event_percpu+0x88/0x118)
	[<c0065b10>] (__handle_irq_event_percpu) from [<c0065bbc>] (handle_irq_event_percpu+0x1c/0x58)
	[<c0065bbc>] (handle_irq_event_percpu) from [<c0065c30>] (handle_irq_event+0x38/0x5c)
	[<c0065c30>] (handle_irq_event) from [<c0068e28>] (handle_level_irq+0xa4/0x130)
	[<c0068e28>] (handle_level_irq) from [<c0064e74>] (generic_handle_irq+0x24/0x34)
	[<c0064e74>] (generic_handle_irq) from [<c021ab7c>] (zynq_gpio_irqhandler+0xb8/0x13c)
	[<c021ab7c>] (zynq_gpio_irqhandler) from [<c0064e74>] (generic_handle_irq+0x24/0x34)
	[<c0064e74>] (generic_handle_irq) from [<c0065370>] (__handle_domain_irq+0x5c/0xb4)
	[<c0065370>] (__handle_domain_irq) from [<c000940c>] (gic_handle_irq+0x48/0x8c)
	[<c000940c>] (gic_handle_irq) from [<c0013e8c>] (__irq_svc+0x6c/0xa8)

To fix this make sure that the trigger is fully initialized before requesting the interrupt.

---
 drivers/iio/imu/adis_trigger.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

@@ -47,6 +47,10 @@ int adis_probe_trigger(struct adis *adis
 	if (adis->trig == NULL)
 		return -ENOMEM;
 
+	adis->trig->dev.parent = &adis->spi->dev;
+	adis->trig->ops = &adis_trigger_ops;
+	iio_trigger_set_drvdata(adis->trig, adis);
+
 	ret = request_irq(adis->spi->irq,
 			  &iio_trigger_generic_data_rdy_poll,
 			  IRQF_TRIGGER_RISING,

@@ -55,9 +59,6 @@ int adis_probe_trigger(struct adis *adis
 	if (ret)
 		goto error_free_trig;
 
-	adis->trig->dev.parent = &adis->spi->dev;
-	adis->trig->ops = &adis_trigger_ops;
-	iio_trigger_set_drvdata(adis->trig, adis);
 	ret = iio_trigger_register(adis->trig);
 
 	indio_dev->trig = iio_trigger_get(adis->trig);

Patches currently in stable-queue which might be from [email protected] are

queue-4.14/iio-adis_lib-initialize-trigger-before-requesting-interrupt.patch