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Message-ID: <20240223170918.00006b16@Huawei.com>
Date: Fri, 23 Feb 2024 17:09:18 +0000
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: Kees Cook <keescook@...omium.org>
CC: Jonathan Cameron <jic23@...nel.org>, Lars-Peter Clausen <lars@...afoo.de>,
Uwe Kleine-König <u.kleine-koenig@...gutronix.de>, Andy
Shevchenko <andriy.shevchenko@...ux.intel.com>, Nuno Sá
<nuno.sa@...log.com>, <linux-iio@...r.kernel.org>, Nathan Chancellor
<nathan@...nel.org>, Nick Desaulniers <ndesaulniers@...gle.com>, "Bill
Wendling" <morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>,
<linux-kernel@...r.kernel.org>, <llvm@...ts.linux.dev>,
<linux-hardening@...r.kernel.org>
Subject: Re: [PATCH] [RFC] iio: pressure: dlhl60d: Check mask_width for IRQs
On Thu, 22 Feb 2024 14:23:39 -0800
Kees Cook <keescook@...omium.org> wrote:
> Clang tripped over a FORTIFY warning in this code, and while it seems it
> may be a false positive in Clang due to loop unwinding, the code in
> question seems to make a lot of assumptions.
Hi Kees,
The assumptions are mostly characteristics of how the IIO buffers work
with the scan masks defined based on indexes in the driver provided
struct iio_chan_spec arrays.
This driver is doing more work than it should need to as we long ago
moved some of the more fiddly handling into the IIO core.
> Comments added, and the
> Clang warning[1] has been worked around by growing the array size.
> Also there was an uninitialized 4th byte in the __be32 array that was
> being sent through to iio_push_to_buffers().
That is indeed not good - the buffer should have been zero initialized.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/2000 [1]
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
> Cc: Jonathan Cameron <jic23@...nel.org>
> Cc: Lars-Peter Clausen <lars@...afoo.de>
> Cc: "Uwe Kleine-König" <u.kleine-koenig@...gutronix.de>
> Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> Cc: "Nuno Sá" <nuno.sa@...log.com>
> Cc: linux-iio@...r.kernel.org
> ---
> drivers/iio/pressure/dlhl60d.c | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/iio/pressure/dlhl60d.c b/drivers/iio/pressure/dlhl60d.c
> index 28c8269ba65d..9bbecd0bfe88 100644
> --- a/drivers/iio/pressure/dlhl60d.c
> +++ b/drivers/iio/pressure/dlhl60d.c
> @@ -250,20 +250,27 @@ static irqreturn_t dlh_trigger_handler(int irq, void *private)
> struct dlh_state *st = iio_priv(indio_dev);
> int ret;
> unsigned int chn, i = 0;
> - __be32 tmp_buf[2];
> + /* This was only an array pair of 4 bytes. */
True, which is the right size as far as I can tell.
If we need this to suppress a warning then comment should say that.
> + __be32 tmp_buf[4] = { };
>
> ret = dlh_start_capture_and_read(st);
> if (ret)
> goto out;
>
> + /* Nothing was checking masklength vs ARRAY_SIZE(tmp_buf)? */
Not needed but no way a compiler could know that.
> + if (WARN_ON_ONCE(indio_dev->masklength > ARRAY_SIZE(tmp_buf)))
> + goto out;
> +
> for_each_set_bit(chn, indio_dev->active_scan_mask,
This is all a bit pointless if not 'wrong' other than the
4th byte uninitialized part. The limit can be hard coded as 2 as
that's a characteristic of this driver.
For device that always read a particular set of channels they
should provide indio_dev->available_scan_masks = { BIT(1) | BIT(0), 0 };
and then always push all the data making this always
memcpy(&tmp_buf[0], &st->rx_buf[1], 3);
mempcy(&tmp_buf[1], &st->rx_buf[1] + 3, 3);
The buffer demux code in the IIO core will deal with repacking the data
if only one channel is enabled.
> indio_dev->masklength) {
> - memcpy(tmp_buf + i,
> + /* This is copying 3 bytes. What about the 4th? */
> + memcpy(&tmp_buf[i],
> &st->rx_buf[1] + chn * DLH_NUM_DATA_BYTES,
> DLH_NUM_DATA_BYTES);
> i++;
> }
>
> + /* How do we know the iio buffer_list has only 2 items? */
Can only include items from the channels array at indexes up to the max
scan_index in there, so 0 and 1 in this case (1 might not be present if only
one channel is enabled). Sizes (and alignment) are given by storagebits so
4 bytes for each.
> iio_push_to_buffers(indio_dev, tmp_buf);
>
> out:
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