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Date: Sat, 8 Jun 2019 06:15:51 +0000
From: Martin Lau <kafai@...com>
To: Stefano Brivio <sbrivio@...hat.com>
CC: David Miller <davem@...emloft.net>, Jianlin Shi <jishi@...hat.com>,
"Wei Wang" <weiwan@...gle.com>, David Ahern <dsahern@...il.com>,
Eric Dumazet <edumazet@...gle.com>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net v2 1/2] ipv6: Dump route exceptions too in
rt6_dump_route()
On Fri, Jun 07, 2019 at 04:14:56AM +0200, Stefano Brivio wrote:
> Since commit 2b760fcf5cfb ("ipv6: hook up exception table to store dst
> cache"), route exceptions reside in a separate hash table, and won't be
> found by walking the FIB, so they won't be dumped to userspace on a
> RTM_GETROUTE message.
>
> This causes 'ip -6 route list cache' and 'ip -6 route flush cache' to
> have no function anymore:
>
> # ip -6 route get fc00:3::1
> fc00:3::1 via fc00:1::2 dev veth_A-R1 src fc00:1::1 metric 1024 expires 539sec mtu 1400 pref medium
> # ip -6 route get fc00:4::1
> fc00:4::1 via fc00:2::2 dev veth_A-R2 src fc00:2::1 metric 1024 expires 536sec mtu 1500 pref medium
> # ip -6 route list cache
> # ip -6 route flush cache
> # ip -6 route get fc00:3::1
> fc00:3::1 via fc00:1::2 dev veth_A-R1 src fc00:1::1 metric 1024 expires 520sec mtu 1400 pref medium
> # ip -6 route get fc00:4::1
> fc00:4::1 via fc00:2::2 dev veth_A-R2 src fc00:2::1 metric 1024 expires 519sec mtu 1500 pref medium
>
> because iproute2 lists cached routes using RTM_GETROUTE, and flushes them
> by listing all the routes, and deleting them with RTM_DELROUTE one by one.
>
> Look up exceptions in the hash table associated with the current fib6_info
> in rt6_dump_route(), and, if present and not expired, add them to the
> dump.
>
> We might be unable to dump all the entries for a given node in a single
> message, so keep track of how many entries were handled for the current
> node in fib6_walker, and skip that amount in case we start from the same
> partially dumped node.
>
> Re-allow userspace to get FIB results by passing the RTM_F_CLONED flag as
> filter, by reverting commit 08e814c9e8eb ("net/ipv6: Bail early if user
> only wants cloned entries").
>
> As we do this, we also have to honour this flag while filtering routes in
> rt6_dump_route() and, if this filter effectively causes some results to be
> discarded, by passing the NLM_F_DUMP_FILTERED flag back.
>
> To flush cached routes, a procfs entry could be introduced instead: that's
> how it works for IPv4. We already have a rt6_flush_exception() function
> ready to be wired to it. However, this would not solve the issue for
> listing, and wouldn't fix the issue with current and previous versions of
> iproute2.
>
> v2: Add tracking of number of entries to be skipped in current node after
> a partial dump. As we restart from the same node, if not all the
> exceptions for a given node fit in a single message, the dump will
> not terminate, as suggested by Martin Lau. This is a concrete
> possibility, setting up a big number of exceptions for the same route
> actually causes the issue, suggested by David Ahern.
>
> Reported-by: Jianlin Shi <jishi@...hat.com>
> Fixes: 2b760fcf5cfb ("ipv6: hook up exception table to store dst cache")
> Signed-off-by: Stefano Brivio <sbrivio@...hat.com>
> ---
> This will cause a non-trivial conflict with commit cc5c073a693f
> ("ipv6: Move exception bucket to fib6_nh") on net-next. I can submit
> an equivalent patch against net-next, if it helps.
>
> include/net/ip6_fib.h | 1 +
> include/net/ip6_route.h | 2 +-
> net/ipv6/ip6_fib.c | 24 ++++++++++-----
> net/ipv6/route.c | 65 +++++++++++++++++++++++++++++++++++++----
> 4 files changed, 78 insertions(+), 14 deletions(-)
>
> diff --git a/include/net/ip6_fib.h b/include/net/ip6_fib.h
> index d6d936cbf6b3..fcac02a8ba74 100644
> --- a/include/net/ip6_fib.h
> +++ b/include/net/ip6_fib.h
> @@ -316,6 +316,7 @@ struct fib6_walker {
> enum fib6_walk_state state;
> unsigned int skip;
> unsigned int count;
> + unsigned int skip_in_node;
> int (*func)(struct fib6_walker *);
> void *args;
> };
> diff --git a/include/net/ip6_route.h b/include/net/ip6_route.h
> index 4790beaa86e0..b66c4aac56ab 100644
> --- a/include/net/ip6_route.h
> +++ b/include/net/ip6_route.h
> @@ -178,7 +178,7 @@ struct rt6_rtnl_dump_arg {
> struct fib_dump_filter filter;
> };
>
> -int rt6_dump_route(struct fib6_info *f6i, void *p_arg);
> +int rt6_dump_route(struct fib6_info *f6i, void *p_arg, unsigned int skip);
> void rt6_mtu_change(struct net_device *dev, unsigned int mtu);
> void rt6_remove_prefsrc(struct inet6_ifaddr *ifp);
> void rt6_clean_tohost(struct net *net, struct in6_addr *gateway);
> diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
> index 008421b550c6..f468fa9b5da6 100644
> --- a/net/ipv6/ip6_fib.c
> +++ b/net/ipv6/ip6_fib.c
> @@ -473,12 +473,22 @@ static int fib6_dump_node(struct fib6_walker *w)
> struct fib6_info *rt;
>
> for_each_fib6_walker_rt(w) {
> - res = rt6_dump_route(rt, w->args);
> - if (res < 0) {
> + res = rt6_dump_route(rt, w->args, w->skip_in_node);
> + if (res) {
> /* Frame is full, suspend walking */
> w->leaf = rt;
> +
> + /* We'll restart from this node, so if some routes were
> + * already dumped, skip them next time.
> + */
> + if (res > 0)
> + w->skip_in_node += res;
> + else
> + w->skip_in_node = 0;
I am likely missing something. It is not obvious to me why skip_in_node
can go backward to 0 here when res < 0.
Should skip_in_node be strictly increasing to ensure forward progress?
Would it be more intuitive to change the return value of
rt6_dump_route() such that
-1: done with this node
>=0: number of routes filled in this round but still some more to be done?
then:
if (res >= 0) {
w->leaf = rt;
w->skip_in_node += res;
return 1;
}
> +
> return 1;
> }
> + w->skip_in_node = 0;
>
> /* Multipath routes are dumped in one route with the
> * RTA_MULTIPATH attribute. Jump 'rt' to point to the
> @@ -530,6 +540,7 @@ static int fib6_dump_table(struct fib6_table *table, struct sk_buff *skb,
> if (cb->args[4] == 0) {
> w->count = 0;
> w->skip = 0;
> + w->skip_in_node = 0;
>
> spin_lock_bh(&table->tb6_lock);
> res = fib6_walk(net, w);
> @@ -545,6 +556,7 @@ static int fib6_dump_table(struct fib6_table *table, struct sk_buff *skb,
> w->state = FWS_INIT;
> w->node = w->root;
> w->skip = w->count;
> + w->skip_in_node = 0;
> } else
> w->skip = 0;
>
> @@ -581,13 +593,10 @@ static int inet6_dump_fib(struct sk_buff *skb, struct netlink_callback *cb)
> } else if (nlmsg_len(nlh) >= sizeof(struct rtmsg)) {
> struct rtmsg *rtm = nlmsg_data(nlh);
>
> - arg.filter.flags = rtm->rtm_flags & (RTM_F_PREFIX|RTM_F_CLONED);
> + if (rtm->rtm_flags & RTM_F_PREFIX)
> + arg.filter.flags = RTM_F_PREFIX;
> }
>
> - /* fib entries are never clones */
> - if (arg.filter.flags & RTM_F_CLONED)
> - goto out;
> -
> w = (void *)cb->args[2];
> if (!w) {
> /* New dump:
> @@ -2045,6 +2054,7 @@ static void fib6_clean_tree(struct net *net, struct fib6_node *root,
> c.w.func = fib6_clean_node;
> c.w.count = 0;
> c.w.skip = 0;
> + c.w.skip_in_node = 0;
> c.func = func;
> c.sernum = sernum;
> c.arg = arg;
> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
> index 848e944f07df..554f88bd64f3 100644
> --- a/net/ipv6/route.c
> +++ b/net/ipv6/route.c
> @@ -4858,12 +4858,16 @@ static bool fib6_info_uses_dev(const struct fib6_info *f6i,
> return false;
> }
>
> -int rt6_dump_route(struct fib6_info *rt, void *p_arg)
> +/* Return count of handled routes on failure, -1 if all failed, 0 on success */
> +int rt6_dump_route(struct fib6_info *rt, void *p_arg, unsigned int skip)
> {
> struct rt6_rtnl_dump_arg *arg = (struct rt6_rtnl_dump_arg *) p_arg;
> struct fib_dump_filter *filter = &arg->filter;
> + struct rt6_exception_bucket *bucket;
> unsigned int flags = NLM_F_MULTI;
> + struct rt6_exception *rt6_ex;
> struct net *net = arg->net;
> + int i, count = 0;
>
> if (rt == net->ipv6.fib6_null_entry)
> return 0;
> @@ -4871,20 +4875,69 @@ int rt6_dump_route(struct fib6_info *rt, void *p_arg)
> if ((filter->flags & RTM_F_PREFIX) &&
> !(rt->fib6_flags & RTF_PREFIX_RT)) {
> /* success since this is not a prefix route */
> - return 1;
> + return 0;
> }
> if (filter->filter_set) {
> if ((filter->rt_type && rt->fib6_type != filter->rt_type) ||
> (filter->dev && !fib6_info_uses_dev(rt, filter->dev)) ||
> (filter->protocol && rt->fib6_protocol != filter->protocol)) {
> - return 1;
> + return 0;
> }
> flags |= NLM_F_DUMP_FILTERED;
> }
>
> - return rt6_fill_node(net, arg->skb, rt, NULL, NULL, NULL, 0,
> - RTM_NEWROUTE, NETLINK_CB(arg->cb->skb).portid,
> - arg->cb->nlh->nlmsg_seq, flags);
> + if (!(filter->flags & RTM_F_CLONED)) {
> + if (skip) {
> + skip--;
> + } else if (rt6_fill_node(net, arg->skb, rt, NULL, NULL, NULL,
> + 0, RTM_NEWROUTE,
> + NETLINK_CB(arg->cb->skb).portid,
> + arg->cb->nlh->nlmsg_seq, flags)) {
> + return -1;
> + } else {
If the v1 email thread will be concluded to dump exceptions only when cloned
flag is set, it may need some changes in this function.
> + count++;
> + }
> + } else {
> + flags |= NLM_F_DUMP_FILTERED;
> + }
> +
> + bucket = rcu_dereference(rt->rt6i_exception_bucket);
> + if (!bucket)
> + return 0;
> +
> + for (i = 0; i < FIB6_EXCEPTION_BUCKET_SIZE; i++) {
> + hlist_for_each_entry(rt6_ex, &bucket->chain, hlist) {
> + if (skip) {
> + skip--;
> + continue;
> + }
> +
> + /* Expiration of entries doesn't bump sernum, insertion
> + * does. Removal is triggered by insertion.
> + *
> + * Count expired entries we go through as handled
> + * entries that we'll skip next time, in case of partial
> + * node dump. Otherwise, if entries expire between two
> + * partial dumps, we'll skip the wrong amount.
> + */
> + if (rt6_check_expired(rt6_ex->rt6i)) {
> + count++;
> + continue;
> + }
> +
> + if (rt6_fill_node(net, arg->skb, rt, &rt6_ex->rt6i->dst,
> + NULL, NULL, 0, RTM_NEWROUTE,
> + NETLINK_CB(arg->cb->skb).portid,
> + arg->cb->nlh->nlmsg_seq, flags)) {
> + return count ? : -1;
> + }
> +
> + count++;
> + }
> + bucket++;
> + }
> +
> + return 0;
> }
>
> static int inet6_rtm_valid_getroute_req(struct sk_buff *skb,
> --
> 2.20.1
>
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