Re: [PATCH v2] Fix NULL pointer deref due to filtering on fork

[Simon Horman <horms@kernel.org>]

On Tue, Oct 10, 2023 at 10:12:25PM -0700, Anjali Kulkarni wrote:
> cn_netlink_send_mult() should be called with filter & filter_data only
> for EXIT case. For all other events, filter & filter_data should be
> NULL.
> 
> Fixes: 2aa1f7a1f47c ("connector/cn_proc: Add filtering to fix some bugs")
> Reported-by: kernel test robot <oliver.sang@intel.com>
> Closes: https://urldefense.com/v3/__https://lore.kernel.org/oe-lkp/202309201456.84c19e27-oliver.sang@intel.com__;!!ACWV5N9M2RV99hQ!PgqlHq_nOe_KlyKkB9Mm_S8QstTJvicjuENwskatuuQK05KPuFw-KvRZeOH8iuEAMjRhkxEMPKJJnLcaT8zrPf9aqNs$

For the record, this got a bit mangled. I believe it should be:

Closes: https://lore.kernel.org/oe-lkp/202309201456.84c19e27-oliver.sang@intel.com/

Also, there is probably no need to resend because of this,
but no blank line here, please.

> Signed-off-by: Anjali Kulkarni <anjali.k.kulkarni@oracle.com>
> ---
>  drivers/connector/cn_proc.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/connector/cn_proc.c b/drivers/connector/cn_proc.c
> index 05d562e9c8b1..01e17f18d187 100644
> --- a/drivers/connector/cn_proc.c
> +++ b/drivers/connector/cn_proc.c
> @@ -104,13 +104,13 @@ static inline void send_msg(struct cn_msg *msg)
>  	if (filter_data[0] == PROC_EVENT_EXIT) {
>  		filter_data[1] =
>  		((struct proc_event *)msg->data)->event_data.exit.exit_code;
> +		cn_netlink_send_mult(msg, msg->len, 0, CN_IDX_PROC, GFP_NOWAIT,
> +				     cn_filter, (void *)filter_data);
>  	} else {
> -		filter_data[1] = 0;
> +		cn_netlink_send_mult(msg, msg->len, 0, CN_IDX_PROC, GFP_NOWAIT,
> +				     NULL, NULL);
>  	}
>  
> -	cn_netlink_send_mult(msg, msg->len, 0, CN_IDX_PROC, GFP_NOWAIT,
> -			     cn_filter, (void *)filter_data);
> -

I am wondering if you considered making cn_filter slightly smarter.
It seems it already understands not to do very much for PROC_EVENT_ALL.

>  	local_unlock(&local_event.lock);
>  }
>  
> -- 
> 2.42.0
> 
>