* [PATCH net] l2tp: remove skb_dst_set() from l2tp_xmit_skb()
@ 2020-07-06 18:02 Xin Long
2020-07-07 17:24 ` James Chapman
2020-07-08 22:25 ` David Miller
0 siblings, 2 replies; 5+ messages in thread
From: Xin Long @ 2020-07-06 18:02 UTC (permalink / raw)
To: network dev; +Cc: davem, James Chapman, Guillaume Nault
In the tx path of l2tp, l2tp_xmit_skb() calls skb_dst_set() to set
skb's dst. However, it will eventually call inet6_csk_xmit() or
ip_queue_xmit() where skb's dst will be overwritten by:
skb_dst_set_noref(skb, dst);
without releasing the old dst in skb. Then it causes dst/dev refcnt leak:
unregister_netdevice: waiting for eth0 to become free. Usage count = 1
This can be reproduced by simply running:
# modprobe l2tp_eth && modprobe l2tp_ip
# sh ./tools/testing/selftests/net/l2tp.sh
So before going to inet6_csk_xmit() or ip_queue_xmit(), skb's dst
should be dropped. This patch is to fix it by removing skb_dst_set()
from l2tp_xmit_skb() and moving skb_dst_drop() into l2tp_xmit_core().
Fixes: 3557baabf280 ("[L2TP]: PPP over L2TP driver core")
Reported-by: Hangbin Liu <liuhangbin@gmail.com>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
---
net/l2tp/l2tp_core.c | 5 +----
1 file changed, 1 insertion(+), 4 deletions(-)
diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
index fcb53ed..df133c24 100644
--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -1028,6 +1028,7 @@ static void l2tp_xmit_core(struct l2tp_session *session, struct sk_buff *skb,
/* Queue the packet to IP for output */
skb->ignore_df = 1;
+ skb_dst_drop(skb);
#if IS_ENABLED(CONFIG_IPV6)
if (l2tp_sk_is_v6(tunnel->sock))
error = inet6_csk_xmit(tunnel->sock, skb, NULL);
@@ -1099,10 +1100,6 @@ int l2tp_xmit_skb(struct l2tp_session *session, struct sk_buff *skb, int hdr_len
goto out_unlock;
}
- /* Get routing info from the tunnel socket */
- skb_dst_drop(skb);
- skb_dst_set(skb, sk_dst_check(sk, 0));
-
inet = inet_sk(sk);
fl = &inet->cork.fl;
switch (tunnel->encap) {
--
2.1.0
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH net] l2tp: remove skb_dst_set() from l2tp_xmit_skb()
2020-07-06 18:02 [PATCH net] l2tp: remove skb_dst_set() from l2tp_xmit_skb() Xin Long
@ 2020-07-07 17:24 ` James Chapman
2020-07-07 20:08 ` Xin Long
2020-07-08 22:25 ` David Miller
1 sibling, 1 reply; 5+ messages in thread
From: James Chapman @ 2020-07-07 17:24 UTC (permalink / raw)
To: Xin Long; +Cc: network dev, davem, Guillaume Nault
On Tue, Jul 07, 2020 at 02:02:32 +0800, Xin Long wrote:
> In the tx path of l2tp, l2tp_xmit_skb() calls skb_dst_set() to set
> skb's dst. However, it will eventually call inet6_csk_xmit() or
> ip_queue_xmit() where skb's dst will be overwritten by:
>
> skb_dst_set_noref(skb, dst);
>
> without releasing the old dst in skb. Then it causes dst/dev refcnt leak:
>
> unregister_netdevice: waiting for eth0 to become free. Usage count = 1
>
> This can be reproduced by simply running:
>
> # modprobe l2tp_eth && modprobe l2tp_ip
> # sh ./tools/testing/selftests/net/l2tp.sh
>
> So before going to inet6_csk_xmit() or ip_queue_xmit(), skb's dst
> should be dropped. This patch is to fix it by removing skb_dst_set()
> from l2tp_xmit_skb() and moving skb_dst_drop() into l2tp_xmit_core().
>
> Fixes: 3557baabf280 ("[L2TP]: PPP over L2TP driver core")
> Reported-by: Hangbin Liu <liuhangbin@gmail.com>
> Signed-off-by: Xin Long <lucien.xin@gmail.com>
> ---
> net/l2tp/l2tp_core.c | 5 +----
> 1 file changed, 1 insertion(+), 4 deletions(-)
>
> diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
> index fcb53ed..df133c24 100644
> --- a/net/l2tp/l2tp_core.c
> +++ b/net/l2tp/l2tp_core.c
> @@ -1028,6 +1028,7 @@ static void l2tp_xmit_core(struct l2tp_session *session, struct sk_buff *skb,
>
> /* Queue the packet to IP for output */
> skb->ignore_df = 1;
> + skb_dst_drop(skb);
> #if IS_ENABLED(CONFIG_IPV6)
> if (l2tp_sk_is_v6(tunnel->sock))
> error = inet6_csk_xmit(tunnel->sock, skb, NULL);
> @@ -1099,10 +1100,6 @@ int l2tp_xmit_skb(struct l2tp_session *session, struct sk_buff *skb, int hdr_len
> goto out_unlock;
> }
>
> - /* Get routing info from the tunnel socket */
> - skb_dst_drop(skb);
> - skb_dst_set(skb, sk_dst_check(sk, 0));
> -
> inet = inet_sk(sk);
> fl = &inet->cork.fl;
> switch (tunnel->encap) {
> --
> 2.1.0
>
This patch doesn't seem right.
For ipv4, the skb dst is used by skb_rtable. In ip_queue_xmit, if
skb_rtable returns a route, it follows the packet_routed label and
skb_dst_set_noref isn't done. Your patch is forcing every ipv4 l2tp
packet to be routed, which isn't what we want.
I ran l2tp.sh and found that the issue happens only for l2tp tests
that use IPv6 IPSec in a routed topology.
Perhaps the real problem is that l2tp shouldn't be using
inet6_csk_xmit and should instead use ip6_xmit?
Please hold off on applying this patch while I look into it.
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH net] l2tp: remove skb_dst_set() from l2tp_xmit_skb()
2020-07-07 17:24 ` James Chapman
@ 2020-07-07 20:08 ` Xin Long
2020-07-08 10:04 ` James Chapman
0 siblings, 1 reply; 5+ messages in thread
From: Xin Long @ 2020-07-07 20:08 UTC (permalink / raw)
To: James Chapman; +Cc: network dev, davem, Guillaume Nault
On Wed, Jul 8, 2020 at 1:24 AM James Chapman <jchapman@katalix.com> wrote:
>
> On Tue, Jul 07, 2020 at 02:02:32 +0800, Xin Long wrote:
> > In the tx path of l2tp, l2tp_xmit_skb() calls skb_dst_set() to set
> > skb's dst. However, it will eventually call inet6_csk_xmit() or
> > ip_queue_xmit() where skb's dst will be overwritten by:
> >
> > skb_dst_set_noref(skb, dst);
> >
> > without releasing the old dst in skb. Then it causes dst/dev refcnt leak:
> >
> > unregister_netdevice: waiting for eth0 to become free. Usage count = 1
> >
> > This can be reproduced by simply running:
> >
> > # modprobe l2tp_eth && modprobe l2tp_ip
> > # sh ./tools/testing/selftests/net/l2tp.sh
> >
> > So before going to inet6_csk_xmit() or ip_queue_xmit(), skb's dst
> > should be dropped. This patch is to fix it by removing skb_dst_set()
> > from l2tp_xmit_skb() and moving skb_dst_drop() into l2tp_xmit_core().
> >
> > Fixes: 3557baabf280 ("[L2TP]: PPP over L2TP driver core")
> > Reported-by: Hangbin Liu <liuhangbin@gmail.com>
> > Signed-off-by: Xin Long <lucien.xin@gmail.com>
> > ---
> > net/l2tp/l2tp_core.c | 5 +----
> > 1 file changed, 1 insertion(+), 4 deletions(-)
> >
> > diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
> > index fcb53ed..df133c24 100644
> > --- a/net/l2tp/l2tp_core.c
> > +++ b/net/l2tp/l2tp_core.c
> > @@ -1028,6 +1028,7 @@ static void l2tp_xmit_core(struct l2tp_session *session, struct sk_buff *skb,
> >
> > /* Queue the packet to IP for output */
> > skb->ignore_df = 1;
> > + skb_dst_drop(skb);
> > #if IS_ENABLED(CONFIG_IPV6)
> > if (l2tp_sk_is_v6(tunnel->sock))
> > error = inet6_csk_xmit(tunnel->sock, skb, NULL);
> > @@ -1099,10 +1100,6 @@ int l2tp_xmit_skb(struct l2tp_session *session, struct sk_buff *skb, int hdr_len
> > goto out_unlock;
> > }
> >
> > - /* Get routing info from the tunnel socket */
> > - skb_dst_drop(skb);
> > - skb_dst_set(skb, sk_dst_check(sk, 0));
> > -
> > inet = inet_sk(sk);
> > fl = &inet->cork.fl;
> > switch (tunnel->encap) {
> > --
> > 2.1.0
> >
>
> This patch doesn't seem right.
Hi James,
>
> For ipv4, the skb dst is used by skb_rtable. In ip_queue_xmit, if
> skb_rtable returns a route, it follows the packet_routed label and
> skb_dst_set_noref isn't done. Your patch is forcing every ipv4 l2tp
> packet to be routed, which isn't what we want.
Without this patch,
it does skb_dst_drop() in l2tp_xmit_skb(),
then do:
skb_dst_set(skb, sk_dst_check(sk, 0));
With this patch:
it does skb_dst_drop() in l2tp_xmit_core()
then in ip_queue_xmit(), it will do:
rt = (struct rtable *)__sk_dst_check(sk, 0);
skb_dst_set_noref(skb, &rt->dst);
so I don't think this patch drops any useful dst for ipv4.
>
> I ran l2tp.sh and found that the issue happens only for l2tp tests
> that use IPv6 IPSec in a routed topology.
>
> Perhaps the real problem is that l2tp shouldn't be using
> inet6_csk_xmit and should instead use ip6_xmit?
>
> Please hold off on applying this patch while I look into it.
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH net] l2tp: remove skb_dst_set() from l2tp_xmit_skb()
2020-07-07 20:08 ` Xin Long
@ 2020-07-08 10:04 ` James Chapman
0 siblings, 0 replies; 5+ messages in thread
From: James Chapman @ 2020-07-08 10:04 UTC (permalink / raw)
To: Xin Long; +Cc: network dev, davem, Guillaume Nault
On Wed, Jul 08, 2020 at 04:08:09 +0800, Xin Long wrote:
> On Wed, Jul 8, 2020 at 1:24 AM James Chapman <jchapman@katalix.com> wrote:
> >
> > On Tue, Jul 07, 2020 at 02:02:32 +0800, Xin Long wrote:
> > > In the tx path of l2tp, l2tp_xmit_skb() calls skb_dst_set() to set
> > > skb's dst. However, it will eventually call inet6_csk_xmit() or
> > > ip_queue_xmit() where skb's dst will be overwritten by:
> > >
> > > skb_dst_set_noref(skb, dst);
> > >
> > > without releasing the old dst in skb. Then it causes dst/dev refcnt leak:
> > >
> > > unregister_netdevice: waiting for eth0 to become free. Usage count = 1
> > >
> > > This can be reproduced by simply running:
> > >
> > > # modprobe l2tp_eth && modprobe l2tp_ip
> > > # sh ./tools/testing/selftests/net/l2tp.sh
> > >
> > > So before going to inet6_csk_xmit() or ip_queue_xmit(), skb's dst
> > > should be dropped. This patch is to fix it by removing skb_dst_set()
> > > from l2tp_xmit_skb() and moving skb_dst_drop() into l2tp_xmit_core().
> > >
> > > Fixes: 3557baabf280 ("[L2TP]: PPP over L2TP driver core")
> > > Reported-by: Hangbin Liu <liuhangbin@gmail.com>
> > > Signed-off-by: Xin Long <lucien.xin@gmail.com>
> > > ---
> > > net/l2tp/l2tp_core.c | 5 +----
> > > 1 file changed, 1 insertion(+), 4 deletions(-)
> > >
> > > diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
> > > index fcb53ed..df133c24 100644
> > > --- a/net/l2tp/l2tp_core.c
> > > +++ b/net/l2tp/l2tp_core.c
> > > @@ -1028,6 +1028,7 @@ static void l2tp_xmit_core(struct l2tp_session *session, struct sk_buff *skb,
> > >
> > > /* Queue the packet to IP for output */
> > > skb->ignore_df = 1;
> > > + skb_dst_drop(skb);
> > > #if IS_ENABLED(CONFIG_IPV6)
> > > if (l2tp_sk_is_v6(tunnel->sock))
> > > error = inet6_csk_xmit(tunnel->sock, skb, NULL);
> > > @@ -1099,10 +1100,6 @@ int l2tp_xmit_skb(struct l2tp_session *session, struct sk_buff *skb, int hdr_len
> > > goto out_unlock;
> > > }
> > >
> > > - /* Get routing info from the tunnel socket */
> > > - skb_dst_drop(skb);
> > > - skb_dst_set(skb, sk_dst_check(sk, 0));
> > > -
> > > inet = inet_sk(sk);
> > > fl = &inet->cork.fl;
> > > switch (tunnel->encap) {
> > > --
> > > 2.1.0
> > >
> >
> > This patch doesn't seem right.
>
> Hi James,
> >
> > For ipv4, the skb dst is used by skb_rtable. In ip_queue_xmit, if
> > skb_rtable returns a route, it follows the packet_routed label and
> > skb_dst_set_noref isn't done. Your patch is forcing every ipv4 l2tp
> > packet to be routed, which isn't what we want.
> Without this patch,
> it does skb_dst_drop() in l2tp_xmit_skb(),
> then do:
> skb_dst_set(skb, sk_dst_check(sk, 0));
>
> With this patch:
> it does skb_dst_drop() in l2tp_xmit_core()
>
> then in ip_queue_xmit(), it will do:
> rt = (struct rtable *)__sk_dst_check(sk, 0);
> skb_dst_set_noref(skb, &rt->dst);
>
> so I don't think this patch drops any useful dst for ipv4.
You're right. My mistake.
Thanks for reporting and fixing this!
> >
> > I ran l2tp.sh and found that the issue happens only for l2tp tests
> > that use IPv6 IPSec in a routed topology.
> >
> > Perhaps the real problem is that l2tp shouldn't be using
> > inet6_csk_xmit and should instead use ip6_xmit?
> >
> > Please hold off on applying this patch while I look into it.
Acked-by: James Chapman <jchapman@katalix.com>
Tested-by: James Chapman <jchapman@katalix.com>
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH net] l2tp: remove skb_dst_set() from l2tp_xmit_skb()
2020-07-06 18:02 [PATCH net] l2tp: remove skb_dst_set() from l2tp_xmit_skb() Xin Long
2020-07-07 17:24 ` James Chapman
@ 2020-07-08 22:25 ` David Miller
1 sibling, 0 replies; 5+ messages in thread
From: David Miller @ 2020-07-08 22:25 UTC (permalink / raw)
To: lucien.xin; +Cc: netdev, jchapman, gnault
From: Xin Long <lucien.xin@gmail.com>
Date: Tue, 7 Jul 2020 02:02:32 +0800
> In the tx path of l2tp, l2tp_xmit_skb() calls skb_dst_set() to set
> skb's dst. However, it will eventually call inet6_csk_xmit() or
> ip_queue_xmit() where skb's dst will be overwritten by:
>
> skb_dst_set_noref(skb, dst);
>
> without releasing the old dst in skb. Then it causes dst/dev refcnt leak:
>
> unregister_netdevice: waiting for eth0 to become free. Usage count = 1
>
> This can be reproduced by simply running:
>
> # modprobe l2tp_eth && modprobe l2tp_ip
> # sh ./tools/testing/selftests/net/l2tp.sh
>
> So before going to inet6_csk_xmit() or ip_queue_xmit(), skb's dst
> should be dropped. This patch is to fix it by removing skb_dst_set()
> from l2tp_xmit_skb() and moving skb_dst_drop() into l2tp_xmit_core().
>
> Fixes: 3557baabf280 ("[L2TP]: PPP over L2TP driver core")
> Reported-by: Hangbin Liu <liuhangbin@gmail.com>
> Signed-off-by: Xin Long <lucien.xin@gmail.com>
Applied and queued up for -stable, thank you.
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2020-07-08 22:25 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
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2020-07-06 18:02 [PATCH net] l2tp: remove skb_dst_set() from l2tp_xmit_skb() Xin Long
2020-07-07 17:24 ` James Chapman
2020-07-07 20:08 ` Xin Long
2020-07-08 10:04 ` James Chapman
2020-07-08 22:25 ` David Miller
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