Subject: Re: [PATCH] netfilter: nfnetlink: fix uninitialized local variable

From: Breno Leitao <[email-masked]>
Date: Thu, 15 Aug 2024 02:04:04 -0700

On Thu, Aug 15, 2024 at 04:27:33PM +0800, icejl wrote:
> In the nfnetlink_rcv_batch function, an uninitialized local variable
> extack is used, which results in using random stack data as a pointer.
> This pointer is then used to access the data it points to and return
> it as the request status, leading to an information leak. If the stack
> data happens to be an invalid pointer, it can cause a pointer access
> exception, triggering a kernel crash.
> 
> Signed-off-by: icejl <[email-masked]>
> ---
>  net/netfilter/nfnetlink.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/net/netfilter/nfnetlink.c b/net/netfilter/nfnetlink.c
> index 4abf660c7baf..b29b281f4b2c 100644
> --- a/net/netfilter/nfnetlink.c
> +++ b/net/netfilter/nfnetlink.c
> @@ -427,6 +427,7 @@ static void nfnetlink_rcv_batch(struct sk_buff *skb, struct nlmsghdr *nlh,
>  
>  	nfnl_unlock(subsys_id);
>  
> +	memset(&extack, 0, sizeof(extack));
>  	if (nlh->nlmsg_flags & NLM_F_ACK)
>  		nfnl_err_add(&err_list, nlh, 0, &extack);

There is a memset later in that function , inside the 
`while (skb->len >= nlmsg_total_size(0))` loop. Should that one be
removed?