Re: [PATCH] powerpc/fadump: reject empty bootargs_append writes

[Sourabh Jain <sourabhjain@linux.ibm.com>]

On 17/04/26 13:09, Pengpeng Hou wrote:
> bootargs_append_store() indexes params[count - 1] when stripping a
> trailing newline from the sysfs write buffer.
>
> kernfs passes zero-length writes through to the store callback, so an
> empty write makes that newline check read before the start of params.
>
> Reject empty writes before looking at the last input byte.
>
> Fixes: 683eab94da75 ("powerpc/fadump: setup additional parameters for dump capture kernel")
> Cc: stable@vger.kernel.org
>
> Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn>
> ---
>   arch/powerpc/kernel/fadump.c | 3 +++
>   1 file changed, 3 insertions(+)
>
> diff --git a/arch/powerpc/kernel/fadump.c b/arch/powerpc/kernel/fadump.c
> index 4ebc333dd786..03ab5565e420 100644
> --- a/arch/powerpc/kernel/fadump.c
> +++ b/arch/powerpc/kernel/fadump.c
> @@ -1479,6 +1479,9 @@ static ssize_t bootargs_append_store(struct kobject *kobj,
>   	if (!fw_dump.fadump_enabled || fw_dump.dump_active)
>   		return -EPERM;
>   
> +	if (!count)
> +		return -EINVAL;

How you manage to call this function with count as 0?

> +
>   	if (count >= COMMAND_LINE_SIZE)
>   		return -EINVAL;
>