linux-kernel - Re: [PATCH v4 1/6] iio: backend: fix out-of-bound write

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Message-ID: <20250511152707.294bc7b9@jic23-huawei>
Date: Sun, 11 May 2025 15:27:07 +0100
From: Jonathan Cameron <jic23@...nel.org>
To: Markus Burri <markus.burri@...com>
Cc: linux-kernel@...r.kernel.org, Mahesh J Salgaonkar
 <mahesh@...ux.ibm.com>, "Oliver O'Halloran" <oohall@...il.com>, Madhavan
 Srinivasan <maddy@...ux.ibm.com>, Michael Ellerman <mpe@...erman.id.au>,
 Nicholas Piggin <npiggin@...il.com>, Christophe Leroy
 <christophe.leroy@...roup.eu>, Naveen N Rao <naveen@...nel.org>, Jacek
 Lawrynowicz <jacek.lawrynowicz@...ux.intel.com>, Maciej Falkowski
 <maciej.falkowski@...ux.intel.com>, Oded Gabbay <ogabbay@...nel.org>, Linus
 Walleij <linus.walleij@...aro.org>, Bartosz Golaszewski <brgl@...ev.pl>,
 Nuno Sa <nuno.sa@...log.com>, Olivier Moysan <olivier.moysan@...s.st.com>,
 Lars-Peter Clausen <lars@...afoo.de>, linuxppc-dev@...ts.ozlabs.org,
 dri-devel@...ts.freedesktop.org, linux-gpio@...r.kernel.org,
 linux-iio@...r.kernel.org, Markus Burri <markus.burri@....ch>
Subject: Re: [PATCH v4 1/6] iio: backend: fix out-of-bound write

On Thu,  8 May 2025 15:06:07 +0200
Markus Burri <markus.burri@...com> 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>
I'm looking for a tag from Nuno on this one before applying.

J
> ---
>  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..31fe793e345e 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))
> +		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);
>