[PATCH 5.10.y] iio: adc: spear: Initialize completion before requesting IRQ

[Maxwell Doose <m32285159@gmail.com>]

In the report from Jaeyoung Chung:

"spear_adc_probe() in drivers/iio/adc/spear_adc.c registers its
interrupt handler with devm_request_irq() before it initializes
st->completion with init_completion(). If an interrupt arrives after
devm_request_irq() and before init_completion(), the handler calls
complete() on an uninitialized completion, causing a kernel panic.

The probe path, in spear_adc_probe():

    iodev = devm_iio_device_alloc(&pdev->dev, sizeof(*st)); /* st kzalloc-zeroed */
    ...
    retval = devm_request_irq(&pdev->dev, irq, spear_adc_isr, 0,
                              LPC32XXAD_NAME, st);           /* register handler */
    ...
    init_completion(&st->completion);                       /* initialize completion */

spear_adc_isr() calls complete():

    complete(&st->completion);

If the device raises an interrupt before init_completion() runs,
complete() acquires the uninitialized wait.lock and walks the zeroed
task_list in swake_up_locked(). The zeroed task_list makes list_empty()
return false, so swake_up_locked() dereferences a NULL list entry,
triggering a KASAN wild-memory-access."

Fix the chance of a spurious IRQ causing an uninitialized pointer
dereference by moving init_completion() above devm_request_irq().

Fixes: b586e5d9eee0 ("staging:iio:adc:spear rename device specific state structure to _state")
Reported-by: Sangyun Kim <sangyun.kim@snu.ac.kr>
Reported-by: Kyungwook Boo <bookyungwook@gmail.com>
Reported-by: Jaeyoung Chung <jjy600901@snu.ac.kr>
Closes: https://lore.kernel.org/linux-iio/20260610115700.774689-1-jjy600901@snu.ac.kr/
Signed-off-by: Maxwell Doose <m32285159@gmail.com>
Reviewed-by: Vladimir Zapolskiy <vz@kernel.org>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
(cherry picked from commit 3ee2128b6f0eb0be7b6cb8f6e0f1f113a65201a0)
Signed-off-by: Maxwell Doose <m32285159@gmail.com>
---
 drivers/iio/adc/spear_adc.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/iio/adc/spear_adc.c b/drivers/iio/adc/spear_adc.c
index 4d4aff88aa6c..12e0811a47b7 100644
--- a/drivers/iio/adc/spear_adc.c
+++ b/drivers/iio/adc/spear_adc.c
@@ -274,6 +274,8 @@ static int spear_adc_probe(struct platform_device *pdev)
 	st = iio_priv(indio_dev);
 	st->np = np;
 
+	init_completion(&st->completion);
+
 	/*
 	 * SPEAr600 has a different register layout than other SPEAr SoC's
 	 * (e.g. SPEAr3xx). Let's provide two register base addresses
@@ -334,8 +336,6 @@ static int spear_adc_probe(struct platform_device *pdev)
 
 	platform_set_drvdata(pdev, indio_dev);
 
-	init_completion(&st->completion);
-
 	indio_dev->name = SPEAR_ADC_MOD_NAME;
 	indio_dev->info = &spear_adc_info;
 	indio_dev->modes = INDIO_DIRECT_MODE;
-- 
2.55.0