Re: [PATCH] netfilter: release skbuf when nlmsg put fail

From: Florian Westphal
Date: Mon Oct 13 2014 - 07:43:32 EST

Houcheng Lin <houcheng@xxxxxxxxx> wrote:
> When system is under heavy loading, the __nfulnl_send() may may failed
> to put nlmsg into skbuf of nfulnl_instance. If not clear the skbuff on failed,
> the __nfulnl_send() will still try to put next nlmsg onto this half-full skbuf
> and cause the user program can never receive packet.
> This patch fix this issue by releasing skbuf immediately after nlmst put
> failed.

Did you observe such problem or is this based on code reading?
I ask because nflog should make sure we always have enough room left in
skb to append a done message, see nfulnl_log_packet():

if (inst->skb &&
size > skb_tailroom(inst->skb) - sizeof(struct nfgenmsg)) {
/* flush skb */

Your patch fixes such 'can never send' skb condition by leaking the
skb. So at the very least you would need to call kfree_skb(), and
perhaps also add WARN_ON() so we catch this and can fix up the size
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