linux-kernel - Re: [PATCH v3] iio: backend: fix out-of-bound write

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Message-ID: <aa7f18ce-9330-4a30-93e5-85489f507a42@baylibre.com>
Date: Tue, 6 May 2025 12:00:19 -0500
From: David Lechner <dlechner@...libre.com>
To: Markus Burri <markus.burri@...com>, linux-kernel@...r.kernel.org
Cc: Nuno Sa <nuno.sa@...log.com>, Olivier Moysan
 <olivier.moysan@...s.st.com>, Jonathan Cameron <jic23@...nel.org>,
 Lars-Peter Clausen <lars@...afoo.de>, linux-iio@...r.kernel.org,
 Markus Burri <markus.burri@....ch>
Subject: Re: [PATCH v3] iio: backend: fix out-of-bound write

On 5/5/25 3:38 PM, Markus Burri wrote:
> The buffer is set to 80 character. If a caller write more characters,
> count is truncated to the max available space in "simple_write_to_buffer".
> But afterwards a string terminator is written to the buffer at offset count
> without boundary check. The zero termination is written OUT-OF-BOUND.
> 
> Add a check that the given buffer is smaller then the buffer to prevent.
> 
> Fixes: 035b4989211d ("iio: backend: make sure to NULL terminate stack buffer")
> Signed-off-by: Markus Burri <markus.burri@...com>
> ---
>  drivers/iio/industrialio-backend.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iio/industrialio-backend.c b/drivers/iio/industrialio-backend.c
> index a43c8d1bb3d0..4a364e038449 100644
> --- a/drivers/iio/industrialio-backend.c
> +++ b/drivers/iio/industrialio-backend.c
> @@ -155,11 +155,14 @@ static ssize_t iio_backend_debugfs_write_reg(struct file *file,
>  	ssize_t rc;
>  	int ret;
>  
> +	if (count >= sizeof(buf) - 1)

Isn't it OK if count == sizeof(buf) - 1? In other words, should be:

	if (count >= sizeof(buf))

> +		return -ENOSPC;
> +
>  	rc = simple_write_to_buffer(buf, sizeof(buf) - 1, ppos, userbuf, count);
>  	if (rc < 0)
>  		return rc;
>  
> -	buf[count] = '\0';
> +	buf[rc] = '\0';
>  
>  	ret = sscanf(buf, "%i %i", &back->cached_reg_addr, &val);
>  
> 
> base-commit: b4432656b36e5cc1d50a1f2dc15357543add530e

It looks like we have the same or similar bugs in:

drivers/accel/ivpu/ivpu_debugfs.c
drivers/gpio/gpio-virtuser.c
drivers/iio/industrialio-core.c
drivers/iio/dac/ad3552r-hs.c

Do you plan to fix these as well?