linux-kernel - Re: [PATCH v2] iio: accel: fxls8962af: Fix use after free in fxls8962af_fifo

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Message-ID: <5zdrnf75n2nfuk3bjzynnj2b57fkptk3lltjf4xaloxorzk27w@6qwdcn5tfynz>
Date: Tue, 03 Jun 2025 13:36:15 +0000
From: Sean Nyekjaer <sean@...nix.com>
To: David Lechner <dlechner@...libre.com>
Cc: Jonathan Cameron <jic23@...nel.org>, Nuno Sá <nuno.sa@...log.com>, Andy Shevchenko <andy@...nel.org>, Jonathan Cameron <Jonathan.Cameron@...wei.com>, linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v2] iio: accel: fxls8962af: Fix use after free in fxls8962af_fifo_flush

On Tue, Jun 03, 2025 at 08:29:51AM +0100, David Lechner wrote:
> On 6/3/25 7:25 AM, Sean Nyekjaer wrote:
> > fxls8962af_fifo_flush() uses indio_dev->active_scan_mask (with
> > iio_for_each_active_channel()) without making sure the indio_dev
> > stays in buffer mode.
> > There is a race if indio_dev exits buffer mode in the middle of the
> > interrupt that flushes the fifo. Fix this by calling
> > synchronize_irq() to ensure that no interrupt is currently running when
> > disabling buffer mode.
> >
> > Unable to handle kernel NULL pointer dereference at virtual address 00000000 when read
> > [...]
> > _find_first_bit_le from fxls8962af_fifo_flush+0x17c/0x290
> > fxls8962af_fifo_flush from fxls8962af_interrupt+0x80/0x178
> > fxls8962af_interrupt from irq_thread_fn+0x1c/0x7c
> > irq_thread_fn from irq_thread+0x110/0x1f4
> > irq_thread from kthread+0xe0/0xfc
> > kthread from ret_from_fork+0x14/0x2c
> >
> > Fixes: 79e3a5bdd9ef ("iio: accel: fxls8962af: add hw buffered sampling")
> > Cc: stable@...r.kernel.org
> > Suggested-by: David Lechner <dlechner@...libre.com>
> > Signed-off-by: Sean Nyekjaer <sean@...nix.com>
> > ---
> > Changes in v2:
> > - As per David's suggestion; switched to use synchronize_irq() instead.
> > - Link to v1: https://lore.kernel.org/r/20250524-fxlsrace-v1-1-dec506dc87ae@geanix.com
> Were you able to find a way to reproduce the bug well enough to
> test this?
> 

Yeah. Sorry I didn't included the reproducer :)

I added:
diff --git a/drivers/iio/accel/fxls8962af-core.c b/drivers/iio/accel/fxls8962af-core.c
index f2558fba491d..ce9a14245f83 100644
--- a/drivers/iio/accel/fxls8962af-core.c
+++ b/drivers/iio/accel/fxls8962af-core.c
@@ -1040,6 +1040,8 @@ static irqreturn_t fxls8962af_interrupt(int irq, void *p)
 	unsigned int reg;
 	int ret;
 
+	usleep_range(10000, 15000);
+
 	ret = regmap_read(data->regmap, FXLS8962AF_INT_STATUS, &reg);
 	if (ret)
 		return IRQ_NONE;

And it was reproduceable within 10 secs:
root@...alhost:/sys/bus/iio/devices/iio:device0/buffer0#
while true; do echo 1 > enable; sleep 1; echo 0 > enable; sleep 1; done

With synchronize_irq(data->irq); I have not been able to reproduce it.

/Sean