linux-kernel - Re: [PATCH v1] Fix NULL pointer dereference in cn

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Message-ID: <20231017080210.GG1751252@kernel.org>
Date:   Tue, 17 Oct 2023 10:02:10 +0200
From:   Simon Horman <horms@...nel.org>
To:     Anjali Kulkarni <anjali.k.kulkarni@...cle.com>
Cc:     linux-kernel@...r.kernel.org, davem@...emloft.net,
        Liam.Howlett@...cle.com, netdev@...r.kernel.org,
        oliver.sang@...el.com, kuba@...nel.org
Subject: Re: [PATCH v1] Fix NULL pointer dereference in cn_filter()

On Fri, Oct 13, 2023 at 03:56:19PM -0700, Anjali Kulkarni wrote:
> Check that sk_user_data is not NULL, else return from cn_filter().

Thanks,

I agree that this change seems likely to address the problem at the link
below. And I also think cn_filter() is a good place to fix this [1].
But I am wondering if you could add some commentary to the patch
description, describing under what circumstances this problem can occur.

[1] https://lore.kernel.org/all/20231013120105.GH29570@kernel.org/

> Fixes: 2aa1f7a1f47c ("connector/cn_proc: Add filtering to fix some bugs")
> Reported-by: kernel test robot <oliver.sang@...el.com>
> Closes: https://lore.kernel.org/oe-lkp/202309201456.84c19e27-oliver.sang@intel.com/
> Signed-off-by: Anjali Kulkarni <anjali.k.kulkarni@...cle.com>
> ---
>  drivers/connector/cn_proc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/connector/cn_proc.c b/drivers/connector/cn_proc.c
> index 05d562e9c8b1..a8e55569e4f5 100644
> --- a/drivers/connector/cn_proc.c
> +++ b/drivers/connector/cn_proc.c
> @@ -54,7 +54,7 @@ static int cn_filter(struct sock *dsk, struct sk_buff *skb, void *data)
>  	enum proc_cn_mcast_op mc_op;
>  	uintptr_t val;
>  
> -	if (!dsk || !data)
> +	if (!dsk || !data || !dsk->sk_user_data)
>  		return 0;
>  
>  	ptr = (__u32 *)data;
> -- 
> 2.42.0
>