From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hannes Frederic Sowa Subject: Re: [PATCH RFC] ipv6: fix route selection if kernel is not compiled with CONFIG_IPV6_ROUTER_PREF Date: Tue, 9 Jul 2013 23:57:01 +0200 Message-ID: <20130709215701.GD9763@order.stressinduktion.org> References: <20130707173031.GC9625@order.stressinduktion.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Cc: netdev@vger.kernel.org, yoshfuji@linux-ipv6.org, petrus.lt@gmail.com, davem@davemloft.net To: nicolas.dichtel@6wind.com Return-path: Received: from s15338416.onlinehome-server.info ([87.106.68.36]:35555 "EHLO order.stressinduktion.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751969Ab3GIV5E (ORCPT ); Tue, 9 Jul 2013 17:57:04 -0400 Content-Disposition: inline In-Reply-To: <20130707173031.GC9625@order.stressinduktion.org> Sender: netdev-owner@vger.kernel.org List-ID: Hello Nicolas! I am currently trying to fix the nexthop selection for kernels compiled without support for CONFIG_IPV6_ROUTER_PREF. I attached my current patch below. While testing I got the following kernel panic in ecmp code: [ 80.144667] ------------[ cut here ]------------ [ 80.145172] kernel BUG at net/ipv6/ip6_fib.c:733! [ 80.145172] invalid opcode: 0000 [#1] SMP [ 80.145172] Modules linked in: 8021q nf_conntrack_netbios_ns nf_conntrack_broadcast ipt_MASQUERADE ip6table_mangle ip6t_REJECT nf_conntrack_ipv6 nf_defrag_ipv6 iptable_nat nf_nat_ipv4 nf_nat iptable_mangle nf_conntrack_ipv4 nf_defrag_ipv4 xt_conntrack nf_conntrack ebtable_filter ebtables ip6table_filter ip6_tables snd_hda_intel snd_hda_codec snd_hwdep snd_seq snd_seq_device snd_pcm snd_page_alloc snd_timer virtio_balloon snd soundcore i2c_piix4 i2c_core virtio_net virtio_blk [ 80.145172] CPU: 1 PID: 786 Comm: ping6 Not tainted 3.10.0+ #118 [ 80.145172] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 [ 80.145172] task: ffff880117fa0000 ti: ffff880118770000 task.ti: ffff880118770000 [ 80.145172] RIP: 0010:[] [] fib6_add+0x75d/0x830 [ 80.145172] RSP: 0018:ffff880118771798 EFLAGS: 00010202 [ 80.145172] RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffff88011350e480 [ 80.145172] RDX: ffff88011350e238 RSI: 0000000000000004 RDI: ffff88011350f738 [ 80.145172] RBP: ffff880118771848 R08: ffff880117903280 R09: 0000000000000001 [ 80.145172] R10: 0000000000000000 R11: 0000000000000000 R12: ffff88011350f680 [ 80.145172] R13: ffff880117903280 R14: ffff880118771890 R15: ffff88011350ef90 [ 80.145172] FS: 00007f02b5127740(0000) GS:ffff88011fd00000(0000) knlGS:0000000000000000 [ 80.145172] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b [ 80.145172] CR2: 00007f981322a000 CR3: 00000001181b1000 CR4: 00000000000006e0 [ 80.145172] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 80.145172] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 [ 80.145172] Stack: [ 80.145172] 0000000000000001 ffff880100000000 ffff880100000000 ffff880117903280 [ 80.145172] 0000000000000000 ffff880119a4cf00 0000000000000400 00000000000007fa [ 80.145172] 0000000000000000 0000000000000000 0000000000000000 ffff88011350f680 [ 80.145172] Call Trace: [ 80.145172] [] ? rt6_bind_peer+0x4b/0x90 [ 80.145172] [] __ip6_ins_rt+0x45/0x70 [ 80.145172] [] ip6_ins_rt+0x35/0x40 [ 80.145172] [] ip6_pol_route.isra.44+0x3a4/0x4b0 [ 80.145172] [] ip6_pol_route_output+0x2a/0x30 [ 80.145172] [] fib6_rule_action+0xd7/0x210 [ 80.145172] [] ? ip6_pol_route_input+0x30/0x30 [ 80.145172] [] fib_rules_lookup+0xc6/0x140 [ 80.145172] [] fib6_rule_lookup+0x44/0x80 [ 80.145172] [] ? ip6_pol_route_input+0x30/0x30 [ 80.145172] [] ip6_route_output+0x73/0xb0 [ 80.145172] [] ip6_dst_lookup_tail+0x2c3/0x2e0 [ 80.145172] [] ? list_del+0x11/0x40 [ 80.145172] [] ? remove_wait_queue+0x3c/0x50 [ 80.145172] [] ip6_dst_lookup_flow+0x3d/0xa0 [ 80.145172] [] rawv6_sendmsg+0x267/0xc20 [ 80.145172] [] inet_sendmsg+0x63/0xb0 [ 80.145172] [] ? selinux_socket_sendmsg+0x23/0x30 [ 80.145172] [] sock_sendmsg+0xa6/0xd0 [ 80.145172] [] SYSC_sendto+0x128/0x180 [ 80.145172] [] ? update_curr+0xec/0x170 [ 80.145172] [] ? kvm_clock_get_cycles+0x9/0x10 [ 80.145172] [] ? __getnstimeofday+0x3e/0xd0 [ 80.145172] [] SyS_sendto+0xe/0x10 [ 80.145172] [] system_call_fastpath+0x16/0x1b [ 80.145172] Code: fe ff ff 41 f6 45 2a 06 0f 85 ca fe ff ff 49 8b 7e 08 4c 89 ee e8 94 ef ff ff e9 b9 fe ff ff 48 8b 82 28 05 00 00 e9 01 ff ff ff <0f> 0b 49 8b 54 24 30 0d 00 00 40 00 89 83 14 01 00 00 48 89 53 [ 80.145172] RIP [] fib6_add+0x75d/0x830 [ 80.145172] RSP [ 80.387413] ---[ end trace 02f20b7a8b81ed95 ]--- [ 80.390154] Kernel panic - not syncing: Fatal exception in interrupt The relevant code is: 725 /* For each sibling in the list, increment the counter of 726 * siblings. BUG() if counters does not match, list of siblings 727 * is broken! 728 */ 729 rt6i_nsiblings = 0; 730 list_for_each_entry_safe(sibling, temp_sibling, 731 &rt->rt6i_siblings, rt6i_siblings) { 732 sibling->rt6i_nsiblings++; 733 BUG_ON(sibling->rt6i_nsiblings != rt->rt6i_nsiblings); 734 rt6i_nsiblings++; 735 } 736 BUG_ON(rt6i_nsiblings != rt->rt6i_nsiblings); 737 } Currently, I don't know if I my patch is to blame or something in the ecmp logic. Another thing I just noticed is: 1240 /* Remove this entry from other siblings */ 1241 if (rt->rt6i_nsiblings) { 1242 struct rt6_info *sibling, *next_sibling; 1243 1244 list_for_each_entry_safe(sibling, next_sibling, 1245 &rt->rt6i_siblings, rt6i_siblings) 1246 sibling->rt6i_nsiblings--; 1247 rt->rt6i_nsiblings = 0; 1248 list_del_init(&rt->rt6i_siblings); 1249 } Are we sure we decrement all sibling's rt6i_nsiblings? Shouldn't we start iterating from fn->leaf? But this does not seem to cause it, because my trace does not report any calls to fib6_del_route. You could try reproduce it by having an interface autoconfigured with a default router with NUD_VALID neighbour. I then added an unused vlan interface (vid 100 in my case) and added the following ip addresses: ip -6 a a 2001:ffff::1/64 dev eth0.100 ip -6 r a 2000::/3 nexthop via 2001:ffff::30 nexthop via 2001:ffff::31 nexthop via 2001:ffff::32 nexthop via 2001:ffff::33 (all nexthops should not be reachable) After starting a ping6 2000::1 the box should panic soon, after the first nexthop entry times out. Perhaps you could give me a hint? Thanks a lot, Hannes [PATCH RFC] ipv6: fix route selection if kernel not compiled with CONFIG_IPV6_ROUTER_PREF This is a follow-up patch to 3630d40067a21d4dfbadc6002bb469ce26ac5d52 ("ipv6: rt6_check_neigh should successfully verify neigh if no NUD information are available"). Since the removal of rt->n in rt6_info we can end up with a dst == NULL in rt6_check_neigh. In case the kernel is not compiled with CONFIG_IPV6_ROUTER_PREF we should also select a route with unkown NUD state but we must not avoid doing round robin selection on routes with the same target. So introduce and pass down a boolean ``do_rr'' to indicate when we should update rt->rr_ptr. As soon as no route is valid we do backtracking and do a lookup on a higher level in the fib trie. To hold correct state on the NUD selection we need to create a neighbour entry as soon as we tried to validate a nexthop. I changed the return value of rt6_check_neigh to: 1 in case of the dst entry validated -1 in case of we had no dst_entry and we need to do rr now -2 in case a we had a dst_entry and it did not validate In case of CONFIG_IPV6_ROUTER_PREF, rt6_probe does not allocate an neighbour entry (!CONFIG_IPV6_ROUTER_PREF: rt6_probe is a nop). Because of this, we have to create a neighbour entry on nexthop validation to track earlier validation errors. We recheck NUD state here to shortcurcuit NUD_NOARP neighbours. This seems to be the least complex fix for stable and net. I'll introduce a new route lookup flag 'idempotent' as soon as next opens to not let ip route get trigger active NUD validation if CONFIG_IPV6_ROUTER_PREF is enabled. Currently we trigger active NUD validation if compiled with CONFIG_IPV6_ROUTER_PREF. It also seems advantageous to make CONFIG_IPV6_ROUTER_PREF a runtime switch and just select the default operation on compile-time. v2: a) improved rt6_check_neigh logic and documented return values Reported-by: Pierre Emeriaud Cc: YOSHIFUJI Hideaki --- net/ipv6/route.c | 62 +++++++++++++++++++++++++++++++++++--------------------- 1 file changed, 39 insertions(+), 23 deletions(-) diff --git a/net/ipv6/route.c b/net/ipv6/route.c index bd5fd70..c5d9e68 100644 --- a/net/ipv6/route.c +++ b/net/ipv6/route.c @@ -531,28 +531,34 @@ static inline int rt6_check_dev(struct rt6_info *rt, int oif) return 0; } -static inline bool rt6_check_neigh(struct rt6_info *rt) +/* This function checks if a neighbour is reachable for routing + * purposes. It returns -2 in case the neighbour should not get + * selected as a viable router, -1 in case it should get selected with + * lowest score and afterwards trying roundrobin. 1 indicates a + * successfull verification. + */ +static inline int rt6_check_neigh(struct rt6_info *rt) { struct neighbour *neigh; - bool ret = false; + int ret = -2; if (rt->rt6i_flags & RTF_NONEXTHOP || !(rt->rt6i_flags & RTF_GATEWAY)) - return true; + return 1; rcu_read_lock_bh(); neigh = __ipv6_neigh_lookup_noref(rt->dst.dev, &rt->rt6i_gateway); if (neigh) { read_lock(&neigh->lock); if (neigh->nud_state & NUD_VALID) - ret = true; + ret = 1; #ifdef CONFIG_IPV6_ROUTER_PREF else if (!(neigh->nud_state & NUD_FAILED)) - ret = true; + ret = 1; #endif read_unlock(&neigh->lock); - } else if (IS_ENABLED(CONFIG_IPV6_ROUTER_PREF)) { - ret = true; + } else { + ret = IS_ENABLED(CONFIG_IPV6_ROUTER_PREF) ? 1 : -1; } rcu_read_unlock_bh(); @@ -566,43 +572,52 @@ static int rt6_score_route(struct rt6_info *rt, int oif, m = rt6_check_dev(rt, oif); if (!m && (strict & RT6_LOOKUP_F_IFACE)) - return -1; + return -2; #ifdef CONFIG_IPV6_ROUTER_PREF m |= IPV6_DECODE_PREF(IPV6_EXTRACT_PREF(rt->rt6i_flags)) << 2; #endif - if (!rt6_check_neigh(rt) && (strict & RT6_LOOKUP_F_REACHABLE)) - return -1; + if (strict & RT6_LOOKUP_F_REACHABLE) { + int n = rt6_check_neigh(rt); + if (n < 0) + return n; + } return m; } static struct rt6_info *find_match(struct rt6_info *rt, int oif, int strict, - int *mpri, struct rt6_info *match) + int *mpri, struct rt6_info *match, + bool *do_rr) { int m; + bool match_do_rr = false; if (rt6_check_expired(rt)) goto out; m = rt6_score_route(rt, oif, strict); - if (m < 0) + if (m == -1 && !IS_ENABLED(CONFIG_IPV6_ROUTER_PREF)) { + match_do_rr = true; + m = 0; /* lowest valid score */ + } else if (m < 0) { goto out; + } + + if (strict & RT6_LOOKUP_F_REACHABLE) + rt6_probe(rt); if (m > *mpri) { - if (strict & RT6_LOOKUP_F_REACHABLE) - rt6_probe(match); + *do_rr = match_do_rr; *mpri = m; match = rt; - } else if (strict & RT6_LOOKUP_F_REACHABLE) { - rt6_probe(rt); } - out: return match; } static struct rt6_info *find_rr_leaf(struct fib6_node *fn, struct rt6_info *rr_head, - u32 metric, int oif, int strict) + u32 metric, int oif, int strict, + bool *do_rr) { struct rt6_info *rt, *match; int mpri = -1; @@ -610,10 +625,10 @@ static struct rt6_info *find_rr_leaf(struct fib6_node *fn, match = NULL; for (rt = rr_head; rt && rt->rt6i_metric == metric; rt = rt->dst.rt6_next) - match = find_match(rt, oif, strict, &mpri, match); + match = find_match(rt, oif, strict, &mpri, match, do_rr); for (rt = fn->leaf; rt && rt != rr_head && rt->rt6i_metric == metric; rt = rt->dst.rt6_next) - match = find_match(rt, oif, strict, &mpri, match); + match = find_match(rt, oif, strict, &mpri, match, do_rr); return match; } @@ -622,15 +637,16 @@ static struct rt6_info *rt6_select(struct fib6_node *fn, int oif, int strict) { struct rt6_info *match, *rt0; struct net *net; + bool do_rr = false; rt0 = fn->rr_ptr; if (!rt0) fn->rr_ptr = rt0 = fn->leaf; - match = find_rr_leaf(fn, rt0, rt0->rt6i_metric, oif, strict); + match = find_rr_leaf(fn, rt0, rt0->rt6i_metric, oif, strict, + &do_rr); - if (!match && - (strict & RT6_LOOKUP_F_REACHABLE)) { + if (do_rr) { struct rt6_info *next = rt0->dst.rt6_next; /* no entries matched; do round-robin */ -- 1.8.1.4