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Message-Id: <20230107002656.b732de6750a063d07cdb8a5f@uniroma2.it>
Date: Sat, 7 Jan 2023 00:26:56 +0100
From: Andrea Mayer <andrea.mayer@...roma2.it>
To: Jonathan Maxwell <jmaxwell37@...il.com>
Cc: Paolo Abeni <pabeni@...hat.com>, davem@...emloft.net,
edumazet@...gle.com, kuba@...nel.org, yoshfuji@...ux-ipv6.org,
dsahern@...nel.org, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org,
Stefano Salsano <stefano.salsano@...roma2.it>,
Paolo Lungaroni <paolo.lungaroni@...roma2.it>,
Ahmed Abdelsalam <ahabdels.dev@...il.com>,
Andrea Mayer <andrea.mayer@...roma2.it>
Subject: Re: [net-next] ipv6: fix routing cache overflow for raw sockets
Hi Jon,
please see after, thanks.
>
> > Any chance you could test this patch based on the latest net-next
> > kernel and let me know the result?
> >
> > diff --git a/include/net/dst_ops.h b/include/net/dst_ops.h
> > index 88ff7bb2bb9b..632086b2f644 100644
> > --- a/include/net/dst_ops.h
> > +++ b/include/net/dst_ops.h
> > @@ -16,7 +16,7 @@ struct dst_ops {
> > unsigned short family;
> > unsigned int gc_thresh;
> >
> > - int (*gc)(struct dst_ops *ops);
> > + void (*gc)(struct dst_ops *ops);
> > struct dst_entry * (*check)(struct dst_entry *, __u32 cookie);
> > unsigned int (*default_advmss)(const struct dst_entry *);
> > unsigned int (*mtu)(const struct dst_entry *);
> > diff --git a/net/core/dst.c b/net/core/dst.c
> > index 6d2dd03dafa8..31c08a3386d3 100644
> > --- a/net/core/dst.c
> > +++ b/net/core/dst.c
> > @@ -82,12 +82,8 @@ void *dst_alloc(struct dst_ops *ops, struct net_device *dev,
> >
> > if (ops->gc &&
> > !(flags & DST_NOCOUNT) &&
> > - dst_entries_get_fast(ops) > ops->gc_thresh) {
> > - if (ops->gc(ops)) {
> > - pr_notice_ratelimited("Route cache is full:
> > consider increasing sysctl net.ipv6.route.max_size.\n");
> > - return NULL;
> > - }
> > - }
> > + dst_entries_get_fast(ops) > ops->gc_thresh)
> > + ops->gc(ops);
> >
> > dst = kmem_cache_alloc(ops->kmem_cachep, GFP_ATOMIC);
> > if (!dst)
> > diff --git a/net/ipv6/route.c b/net/ipv6/route.c
> > index e74e0361fd92..b643dda68d31 100644
> > --- a/net/ipv6/route.c
> > +++ b/net/ipv6/route.c
> > @@ -91,7 +91,7 @@ static struct dst_entry *ip6_negative_advice(struct
> > dst_entry *);
> > static void ip6_dst_destroy(struct dst_entry *);
> > static void ip6_dst_ifdown(struct dst_entry *,
> > struct net_device *dev, int how);
> > -static int ip6_dst_gc(struct dst_ops *ops);
> > +static void ip6_dst_gc(struct dst_ops *ops);
> >
> > static int ip6_pkt_discard(struct sk_buff *skb);
> > static int ip6_pkt_discard_out(struct net *net, struct
> > sock *sk, struct sk_buff *skb);
> > @@ -3284,11 +3284,10 @@ struct dst_entry *icmp6_dst_alloc(struct
> > net_device *dev,
> > return dst;
> > }
> >
> > -static int ip6_dst_gc(struct dst_ops *ops)
> > +static void ip6_dst_gc(struct dst_ops *ops)
> > {
> > struct net *net = container_of(ops, struct net, ipv6.ip6_dst_ops);
> > int rt_min_interval = net->ipv6.sysctl.ip6_rt_gc_min_interval;
> > - int rt_max_size = net->ipv6.sysctl.ip6_rt_max_size;
> > int rt_elasticity = net->ipv6.sysctl.ip6_rt_gc_elasticity;
> > int rt_gc_timeout = net->ipv6.sysctl.ip6_rt_gc_timeout;
> > unsigned long rt_last_gc = net->ipv6.ip6_rt_last_gc;
> > @@ -3296,11 +3295,10 @@ static int ip6_dst_gc(struct dst_ops *ops)
> > int entries;
> >
> > entries = dst_entries_get_fast(ops);
> > - if (entries > rt_max_size)
> > + if (entries > ops->gc_thresh)
> > entries = dst_entries_get_slow(ops);
> >
> > - if (time_after(rt_last_gc + rt_min_interval, jiffies) &&
> > - entries <= rt_max_size)
> > + if (time_after(rt_last_gc + rt_min_interval, jiffies))
> > goto out;
> >
> > fib6_run_gc(atomic_inc_return(&net->ipv6.ip6_rt_gc_expire), net, true);
> > @@ -3310,7 +3308,6 @@ static int ip6_dst_gc(struct dst_ops *ops)
> > out:
> > val = atomic_read(&net->ipv6.ip6_rt_gc_expire);
> > atomic_set(&net->ipv6.ip6_rt_gc_expire, val - (val >> rt_elasticity));
> > - return entries > rt_max_size;
> > }
> >
> > static int ip6_nh_lookup_table(struct net *net, struct fib6_config *cfg,
> > @@ -6512,7 +6509,7 @@ static int __net_init ip6_route_net_init(struct net *net)
> > #endif
> >
> > net->ipv6.sysctl.flush_delay = 0;
> > - net->ipv6.sysctl.ip6_rt_max_size = 4096;
> > + net->ipv6.sysctl.ip6_rt_max_size = INT_MAX;
> > net->ipv6.sysctl.ip6_rt_gc_min_interval = HZ / 2;
> > net->ipv6.sysctl.ip6_rt_gc_timeout = 60*HZ;
> > net->ipv6.sysctl.ip6_rt_gc_interval = 30*HZ;
> >
>
> Yes, I will apply this patch in the next days and check how it deals with the
> seg6 subsystem. I will keep you posted.
>
I applied the patch* to the net-next (HEAD 6bd4755c7c49) and did some tests on
the seg6 subsystem, specifically running the End.X/DX6 behaviors. They seem to
work fine.
(*) I had to slightly edit the patch because of the code formatting, e.g.
some incorrect line breaks, spaces, etc.
Ciao,
Andrea
>
> > On Sat, Dec 24, 2022 at 6:38 PM Jonathan Maxwell <jmaxwell37@...il.com> wrote:
> > >
> > > On Sat, Dec 24, 2022 at 7:28 AM Andrea Mayer <andrea.mayer@...roma2.it> wrote:
> > > >
> > > > Hi Jon,
> > > > please see below, thanks.
> > > >
> > > > On Wed, 21 Dec 2022 08:48:11 +1100
> > > > Jonathan Maxwell <jmaxwell37@...il.com> wrote:
> > > >
> > > > > On Tue, Dec 20, 2022 at 11:35 PM Paolo Abeni <pabeni@...hat.com> wrote:
> > > > > >
> > > > > > On Mon, 2022-12-19 at 10:48 +1100, Jon Maxwell wrote:
> > > > > > > Sending Ipv6 packets in a loop via a raw socket triggers an issue where a
> > > > > > > route is cloned by ip6_rt_cache_alloc() for each packet sent. This quickly
> > > > > > > consumes the Ipv6 max_size threshold which defaults to 4096 resulting in
> > > > > > > these warnings:
> > > > > > >
> > > > > > > [1] 99.187805] dst_alloc: 7728 callbacks suppressed
> > > > > > > [2] Route cache is full: consider increasing sysctl net.ipv6.route.max_size.
> > > > > > > .
> > > > > > > .
> > > > > > > [300] Route cache is full: consider increasing sysctl net.ipv6.route.max_size.
> > > > > >
> > > > > > If I read correctly, the maximum number of dst that the raw socket can
> > > > > > use this way is limited by the number of packets it allows via the
> > > > > > sndbuf limit, right?
> > > > > >
> > > > >
> > > > > Yes, but in my test sndbuf limit is never hit so it clones a route for
> > > > > every packet.
> > > > >
> > > > > e.g:
> > > > >
> > > > > output from C program sending 5000000 packets via a raw socket.
> > > > >
> > > > > ip raw: total num pkts 5000000
> > > > >
> > > > > # bpftrace -e 'kprobe:dst_alloc {@...nt[comm] = count()}'
> > > > > Attaching 1 probe...
> > > > >
> > > > > @count[a.out]: 5000009
> > > > >
> > > > > > Are other FLOWI_FLAG_KNOWN_NH users affected, too? e.g. nf_dup_ipv6,
> > > > > > ipvs, seg6?
> > > > > >
> > > > >
> > > > > Any call to ip6_pol_route(s) where no res.nh->fib_nh_gw_family is 0 can do it.
> > > > > But we have only seen this for raw sockets so far.
> > > > >
> > > >
> > > > In the SRv6 subsystem, the seg6_lookup_nexthop() is used by some
> > > > cross-connecting behaviors such as End.X and End.DX6 to forward traffic to a
> > > > specified nexthop. SRv6 End.X/DX6 can specify an IPv6 DA (i.e., a nexthop)
> > > > different from the one carried by the IPv6 header. For this purpose,
> > > > seg6_lookup_nexthop() sets the FLOWI_FLAG_KNOWN_NH.
> > > >
> > > Hi Andrea,
> > >
> > > Thanks for pointing that datapath out. The more generic approach we are
> > > taking bringing Ipv6 closer to Ipv4 in this regard should fix all instances
> > > of this.
> > >
> > > > > > > [1] 99.187805] dst_alloc: 7728 callbacks suppressed
> > > > > > > [2] Route cache is full: consider increasing sysctl net.ipv6.route.max_size.
> > > > > > > .
> > > > > > > .
> > > > > > > [300] Route cache is full: consider increasing sysctl net.ipv6.route.max_size.
> > > >
> > > > I can reproduce the same warning messages reported by you, by instantiating an
> > > > End.X behavior whose nexthop is handled by a route for which there is no "via".
> > > > In this configuration, the ip6_pol_route() (called by seg6_lookup_nexthop())
> > > > triggers ip6_rt_cache_alloc() because i) the FLOWI_FLAG_KNOWN_NH is present ii)
> > > > and the res.nh->fib_nh_gw_family is 0 (as already pointed out).
> > > >
> > >
> > > Nice, when I get back after the holiday break I'll submit the next patch. It
> > > would be great if you could test the new patch and let me know how it works in
> > > your tests at that juncture. I'll keep you posted.
> > >
> > > Regards
> > >
> > > Jon
> > >
> > > > > Regards
> > > > >
> > > > > Jon
> > > >
> > > > Ciao,
> > > > Andrea
>
>
> --
> Andrea Mayer <andrea.mayer@...roma2.it>
--
Andrea Mayer <andrea.mayer@...roma2.it>
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