Re: [RFC PATCH net-next] ipvs: add missing lock in ip_vs_ftp_init_conn()

[Xiaotian Feng <xtfeng@gmail.com>]

On Fri, Jun 29, 2012 at 5:04 PM, Julian Anastasov <ja@ssi.bg> wrote:
>
>         Hello,
>
> On Fri, 29 Jun 2012, Xiaotian Feng wrote:
>
>> > On Thu, 28 Jun 2012, Xiaotian Feng wrote:
>> >
>> >> We met a kernel panic in 2.6.32.43 kernel:
>> >>
>> >> [2680191.848044] IPVS: ip_vs_conn_hash(): request for already hashed, called from run_timer_softirq+0x175/0x1d0
>> >> <snip>
>> >> [2680311.849009] general protection fault: 0000 [#1] SMP
>
>         What we see here is 120 seconds between 2680191 and
> 2680311. It can mean 2 things:
>
> - some state timeout, it depends on your forwarding method.
> What is it? NAT? DR?
>
> - 60 seconds for ip_vs_conn_expire retries
>
>> >> After code review, the only chance that kernel change connection flag without protection is
>> >> in ip_vs_ftp_init_conn().
>> >
>> >        Hm, ip_vs_ftp_init_conn is called before 1st hashing,
>> > from ip_vs_bind_app() in ip_vs_conn_new() before
>> > ip_vs_conn_hash(). It should be another problem with
>> > the flags. How different is IPVS in 2.6.32.43 compared to
>> > recent kernels? If commit aea9d711 is present, I'm not
>> > aware of other similar problems.
>>
>> ip_vs_bind_app() is also called by ip_vs_try_bind_dest(), which can be
>> traced to ip_vs_proc_conn().
>> I've checked the changes in upstream, but nothing helps since aea9d711
>> has been taken into 2.6.32.28 kernel.
>
>         OK, this fix should make it safe for master-backup
> sync and it should be applied but I suspect you are not
> using sync, right? And then this fix will not solve the oops.
>

We're using sync.

>         There are no many places that rehash conn:
>
> ip_vs_conn_fill_cport
>         - used for FTP
>
> ip_vs_check_template:
>         - do you have persistence configured?

No.

>
>         After you provide details for the used forwarding
> method, persistence and sync we should think how such races
> with rehashing can lead to double hlist_del. May be
> you can modify the debug message in ip_vs_conn_hash, so
> that we can see cp->flags and ntohs of cp->cport, cp->dport
> and cp->vport when oops happens again.

I just found 2.6.32.34 kernel differ from upstream kernel,  2.6.32
kernel doesn't have ip_vs_try_bind_dest(), but ip_vs_process_message()
kernel might change conn flags without lock protection. This is fixed in
commit f73181c, following changes:

@@ -834,6 +843,7 @@ static void ip_vs_proc_conn(struct net *net,
struct ip_vs_conn_param *param,
                kfree(param->pe_data);

                dest = cp->dest;
+               spin_lock(&cp->lock);
                if ((cp->flags ^ flags) & IP_VS_CONN_F_INACTIVE &&
                    !(flags & IP_VS_CONN_F_TEMPLATE) && dest) {
                        if (flags & IP_VS_CONN_F_INACTIVE) {
@@ -847,6 +857,7 @@ static void ip_vs_proc_conn(struct net *net,
struct ip_vs_conn_param *param,
                flags &= IP_VS_CONN_F_BACKUP_UPD_MASK;
                flags |= cp->flags & ~IP_VS_CONN_F_BACKUP_UPD_MASK;
                cp->flags = flags;
+               spin_unlock(&cp->lock);
                if (!dest) {
                        dest = ip_vs_try_bind_dest(cp);
                        if (dest)

So I took this part into 2.6.32 kernel. But I still think the patch I
posted is required for upstream kernel. Even though there are no many
places that rehash conn, this is potential race as cp->flags is not
protected.

Thanks.

>
> Regards
>
> --
> Julian Anastasov <ja@ssi.bg>