Subject: Re: [PATCH v3] af_netlink: ensure that NLMSG_DONE never fails in dumps

From: Johannes Berg <[email-masked]>
Date: Thu, 09 Nov 2017 03:02:14 +0100

On Thu, 2017-11-09 at 10:42 +0900, Jason A. Donenfeld wrote:
> +++ b/net/netlink/af_netlink.c
> @@ -2136,7 +2136,7 @@ static int netlink_dump(struct sock *sk)
>  	struct sk_buff *skb = NULL;
>  	struct nlmsghdr *nlh;
>  	struct module *module;
> -	int len, err = -ENOBUFS;
> +	int err = -ENOBUFS;
>  	int alloc_min_size;
>  	int alloc_size;
>  
> @@ -2183,9 +2183,10 @@ static int netlink_dump(struct sock *sk)
>  	skb_reserve(skb, skb_tailroom(skb) - alloc_size);
>  	netlink_skb_set_owner_r(skb, sk);
>  
> -	len = cb->dump(skb, cb);
> +	if (nlk->dump_done_errno > 0)
> +		nlk->dump_done_errno = cb->dump(skb, cb);
>  
> -	if (len > 0) {
> +	if (nlk->dump_done_errno > 0 || skb_tailroom(skb) < nlmsg_total_size(sizeof(nlk->dump_done_errno))) {
>  		mutex_unlock(nlk->cb_mutex);

nit: I think your line got a little long here :)
 
> -	memcpy(nlmsg_data(nlh), &len, sizeof(len));
> +	memcpy(nlmsg_data(nlh), &nlk->dump_done_errno, sizeof(nlk->dump_done_errno));

and here

> +	nlk->dump_done_errno = INT_MAX;

I guess positive values aren't really returned from dump?

johannes