Re: ping -I eth1 ....

[Eric Dumazet <eric.dumazet@gmail.com>]

Le mercredi 17 novembre 2010 à 10:29 +0100, Joakim Tjernlund a écrit :
> Joakim Tjernlund/Transmode wrote on 2010/11/09 20:33:37:
> >
> > Joakim Tjernlund/Transmode wrote on 2010/11/06 10:42:46:
> > > Thomas Graf <tgr@infradead.org> wrote on 2010/11/05 21:31:50:
> > > >
> > > > On Fri, Nov 05, 2010 at 04:54:18PM +0100, Joakim Tjernlund wrote:
> > > > > Eric Dumazet <eric.dumazet@gmail.com> wrote on 2010/11/05 16:06:54:
> > > > > >
> > > > > > > Hopefully most of that is legacy or just plain wrong? Unless
> > > > > > > someone can say why only test IFF_UP one should consider changing them.
> > > > > > >
> > > > > >
> > > > > > Most of the places are hot path.
> > > > > >
> > > > > > You dont want to replace one test by four tests.
> > > > > >
> > > > > > _This_ would be wrong :)
> > > > >
> > > > > Wrong is wrong, even if it is in the hot path :)
> > > > > Perhaps it is time define and internal IFF_OPERATIONAL flag
> > > > > which is the sum of IFF_UP, IFF_RUNNING etc.? Tht
> > > > > way you still get one test in the hot path and can abstract
> > > > > what defines an operational link.
> > > >
> > > > You definitely don't want to have your send() call fail simply because
> > > > the carrier was off for a few msec or the routing daemon has put a link
> > > > down temporarly. Also, the outgoing interface looked up at routing
> > > > decision is not necessarly the interface used for sending in the end.
> > > > The packet may get mangled and rerouted by netfilter or tc on the way.
> > >
> > > But do you handle the case when the link is non operational for a long time?
> > >
> > > >
> > > > Personally I'm even ok with the current behaviour of sendto() while the
> > > > socket is bound to an interface but if we choose to return an error
> > > > if the interface is down we might as well do so based on the operational
> > > > status.
> 
> > > Perhaps there is a better way. This all started when pppd hung because
> > > of ping -I <ppp interface>, then someone pulled the cable for the on the link.
> > >
> > > This is a strace where we have two ping -I,
> > > ping -I p1-2-1-2-2 .. and ping -I p1-2-3-2-4 ..
> > > Notice how pppd hangs for a long time in PPPIOCDETACH
> > > As far as I can tell this is due to ping -I has claimed the ppp interfaces
> > > and doesn't noticed that the link is down. Ideally ping should receive
> > > a ENODEV as soon as pppd calls PPPIOCDETACH.
> > >
> > >    0.000908 write(0, "Connection terminated.\n", 23) = 23
> > >      0.000481 gettimeofday({1288952770, 566048}, NULL) = 0
> > >      0.001553 ioctl(7, PPPIOCDETACH
> > > Message from syslogd@Brazil at Fri Nov  5 11:26:20 2010 ...
> > > Brazil kernel: unregister_netdevice: waiting for p1-2-1-2-2 to become free. Usage count = 3
> > > Message from syslogd@Brazil at Fri Nov  5 11:26:20 2010 ...
> > > Brazil kernel: unregister_netdevice: waiting for p1-2-3-2-4 to become free. Usage count = 3
> > > Message from syslogd@Brazil at Fri Nov  5 11:26:51 2010 ...
> > > Brazil last message repeated 3 times
> > > , 0xbfbc3398) = 0
> > >     66.559216 connect(9, {sa_family=AF_PPPOX, sa_data="\0\0\0\0\0\0\0\252\273\314\335\356hd"}, 30) = 0
> > >      0.000693 close(10)                 = 0
> > >      0.000449 close(7)                  = 0
> > >      0.009801 close(9)                  = 0
> >
> > Any comment on this last strace? It is expected that ping -I should
> > hold pppd hostage?
> >
> 
> Ping?
> 

I thought I posted a patch, is there something else ?

Could you please test with latest net-next-2.6 and following patch ?


Thanks

[PATCH net-next-2.6] ipv4: dont create a route if device is down

ip_route_output_slow() should not create a route if device is down, so
that we report -ENETUNREACH error to users.

Reported-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Reported-by: Joakim Tjernlund <joakim.tjernlund@transmode.se>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
---
 net/ipv4/route.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 66610ea..3cc4191 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -2559,8 +2559,11 @@ static int ip_route_output_slow(struct net *net, struct rtable **rp,
 			goto out;
 
 		/* RACE: Check return value of inet_select_addr instead. */
-		if (rcu_dereference(dev_out->ip_ptr) == NULL)
-			goto out;	/* Wrong error code */
+		if (!(dev_out->flags & IFF_UP) ||
+		    rcu_dereference(dev_out->ip_ptr) == NULL) {
+			err = -ENETUNREACH;
+			goto out;
+		}
 
 		if (ipv4_is_local_multicast(oldflp->fl4_dst) ||
 		    ipv4_is_lbcast(oldflp->fl4_dst)) {