Subject: Re: [PATCH v2] netfilter: release skbuf when nlmsg put fail

From: Florian Westphal <[email-masked]>
Date: Tue, 14 Oct 2014 19:27:46 +0200

Houcheng Lin <[email-masked]> wrote:
> 2014-10-14 18:49 GMT+08:00 Florian Westphal <[email-masked]>:
> > Houcheng Lin <[email-masked]> 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.
> >
> > Could you please try this patch on top of this one and see if the
> > WARN_ON goes away?
> >
> > Thanks
> >
> > diff --git a/net/netfilter/nfnetlink_log.c b/net/netfilter/nfnetlink_log.c
> > --- a/net/netfilter/nfnetlink_log.c
> > +++ b/net/netfilter/nfnetlink_log.c
> > @@ -649,7 +649,8 @@ nfulnl_log_packet(struct net *net,
> >                 + nla_total_size(sizeof(u_int32_t))     /* gid */
> >                 + nla_total_size(plen)                  /* prefix */
> >                 + nla_total_size(sizeof(struct nfulnl_msg_packet_hw))
> > -               + nla_total_size(sizeof(struct nfulnl_msg_packet_timestamp));
> > +               + nla_total_size(sizeof(struct nfulnl_msg_packet_timestamp))
> > +               + nla_total_size(sizeof(struct nfgenmsg));      /* NLMSG_DONE */
> >
> >         if (in && skb_mac_header_was_set(skb)) {
> >                 size +=   nla_total_size(skb->dev->hard_header_len)
> > @@ -692,8 +693,7 @@ nfulnl_log_packet(struct net *net,
> >                 goto unlock_and_release;
> >         }
> >
> > -       if (inst->skb &&
> > -           size > skb_tailroom(inst->skb) - sizeof(struct nfgenmsg)) {
> > +       if (inst->skb && size > skb_tailroom(inst->skb)) {
> >                 /* either the queue len is too high or we don't have
> >                  * enough room in the skb left. flush to userspace. */
> >                 __nfulnl_flush(inst);
> Hi Florian,
> The modified code seems won't affect the program flow: Size is add a
> extra value,
> sizeof(struct nfgenmsg), during initialization. comparison size with tailroom
> space, the right-side value also add the same value.

There are two changes:

sizeof(struct nfgenmsg) is not the same as nla_total_size(sizeof(struct
nfgenmsg)).

Also, adding it means we consider the DONE space when allocationg the
skb.