Re: [PATCH v2] iio: dac: ad3552r-hs: fix out-of-bound write in ad3552r_hs_write_data_source

[Nuno Sá]

On Wed, 2026-01-07 at 22:35 +0800, Miaoqian Lin wrote:
> When simple_write_to_buffer() succeeds, it returns the number of bytes
> actually copied to the buffer. The code incorrectly uses 'count'
> as the index for null termination instead of the actual bytes copied.
> If count exceeds the buffer size, this leads to out-of-bounds write.
> Add a check for the count and use the return value as the index.
> 
> The bug was validated using a demo module that mirrors the original
> code and was tested under QEMU.
> 
> Pattern of the bug:
> - A fixed 64-byte stack buffer is filled using count.
> - If count > 64, the code still does buf[count] = '\0', causing an
> - out-of-bounds write on the stack.
> 
> Steps for reproduce:
> - Opens the device node.
> - Writes 128 bytes of A to it.
> - This overflows the 64-byte stack buffer and KASAN reports the OOB.
> 
> Found via static analysis. This is similar to the
> commit da9374819eb3 ("iio: backend: fix out-of-bound write")
> 
> Fixes: b1c5d68ea66e ("iio: dac: ad3552r-hs: add support for internal ramp")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Miaoqian Lin <linmq006@xxxxxxxxx>
> ---

Reviewed-by: Nuno Sá <nuno.sa@xxxxxxxxxx>

> changes in v2:
> - update commit message
> - v1 link: https://lore.kernel.org/all/20251027150713.59067-1-linmq006@xxxxxxxxx/
> ---
>  drivers/iio/dac/ad3552r-hs.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iio/dac/ad3552r-hs.c b/drivers/iio/dac/ad3552r-hs.c
> index 41b96b48ba98..a9578afa7015 100644
> --- a/drivers/iio/dac/ad3552r-hs.c
> +++ b/drivers/iio/dac/ad3552r-hs.c
> @@ -549,12 +549,15 @@ static ssize_t ad3552r_hs_write_data_source(struct file *f,
>  
>  	guard(mutex)(&st->lock);
>  
> +	if (count >= sizeof(buf))
> +		return -ENOSPC;
> +
>  	ret = simple_write_to_buffer(buf, sizeof(buf) - 1, ppos, userbuf,
>  				     count);
>  	if (ret < 0)
>  		return ret;
>  
> -	buf[count] = '\0';
> +	buf[ret] = '\0';
>  
>  	ret = match_string(dbgfs_attr_source, ARRAY_SIZE(dbgfs_attr_source),
>  			   buf);