From: Guillaume Nault gnault@redhat.com

__peernet2id() can be protected by RCU as it only calls idr_for_each(), which is RCU-safe, and never modifies the nsid table.

rtnl_net_dumpid() can also do lockless lookups. It does two nested idr_for_each() calls on nsid tables (one direct call and one indirect call because of rtnl_net_dumpid_one() calling __peernet2id()). The netnsid tables are never updated. Therefore it is safe to not take the nsid_lock and run within an RCU-critical section instead.

Signed-off-by: Guillaume Nault gnault@redhat.com Signed-off-by: David S. Miller davem@davemloft.net

A nice side-effect of replacing spin_{lock,unlock}_bh() with rcu_spin_{lock,unlock}() in peernet2id() is that it avoids the situation where SoftIRQs get enabled whilst IRQs are turned off.

From bugzilla.redhat.com/show_bug.cgi?id=1384179 (an ancient

4.9.0-0.rc0 kernel):

dump_stack+0x86/0xc3 __warn+0xcb/0xf0 warn_slowpath_null+0x1d/0x20 __local_bh_enable_ip+0x9d/0xc0 _raw_spin_unlock_bh+0x35/0x40 peernet2id+0x54/0x80 netlink_broadcast_filtered+0x220/0x3c0 netlink_broadcast+0x1d/0x20 audit_log+0x6a/0x90 security_set_bools+0xee/0x200 []

Note, security_set_bools() calls write_lock_irq(). peernet2id() calls spin_unlock_bh().

From an internal (UEK) stack trace based on the v4.14.35 kernel (LTS

4.14.231):

queued_spin_lock_slowpath+0xb/0xf _raw_spin_lock_irqsave+0x46/0x48 send_mad+0x3d2/0x590 [ib_core] ib_sa_path_rec_get+0x223/0x4d0 [ib_core] path_rec_start+0xa3/0x140 [ib_ipoib] ipoib_start_xmit+0x2b0/0x6a0 [ib_ipoib] dev_hard_start_xmit+0xb2/0x237 sch_direct_xmit+0x114/0x1bf __dev_queue_xmit+0x592/0x818 dev_queue_xmit+0x10/0x12 arp_xmit+0x38/0xa6 arp_send_dst.part.16+0x61/0x84 arp_process+0x825/0x889 arp_rcv+0x140/0x1c9 __netif_receive_skb_core+0x401/0xb39 __netif_receive_skb+0x18/0x59 netif_receive_skb_internal+0x45/0x119 napi_gro_receive+0xd8/0xf6 ipoib_ib_handle_rx_wc+0x1ca/0x520 [ib_ipoib] ipoib_poll+0xcd/0x150 [ib_ipoib] net_rx_action+0x289/0x3f4 __do_softirq+0xe1/0x2b5 do_softirq_own_stack+0x2a/0x35 </IRQ> do_softirq+0x4d/0x6a __local_bh_enable_ip+0x57/0x59 _raw_spin_unlock_bh+0x23/0x25 peernet2id+0x51/0x73 netlink_broadcast_filtered+0x223/0x41b netlink_broadcast+0x1d/0x1f rdma_nl_multicast+0x22/0x30 [ib_core] send_mad+0x3e5/0x590 [ib_core] ib_sa_path_rec_get+0x223/0x4d0 [ib_core] rdma_resolve_route+0x287/0x810 [rdma_cm] rds_rdma_cm_event_handler_cmn+0x311/0x7d0 [rds_rdma] rds_rdma_cm_event_handler_worker+0x22/0x30 [rds_rdma] process_one_work+0x169/0x3a6 worker_thread+0x4d/0x3e5 kthread+0x105/0x138 ret_from_fork+0x24/0x49

Here, pay attention to ib_nl_make_request() which calls spin_lock_irqsave() on a global lock just before calling rdma_nl_multicast(). Thereafter, peernet2id() enables SoftIRQs, and ipoib starts and calls the same path and ends up trying to acquire the same global lock again.

(cherry picked from commit 2dce224f469f060b9998a5a869151ef83c08ce77) Fixes: fba143c66abb ("netns: avoid disabling irq for netns id") Signed-off-by: Håkon Bugge haakon.bugge@oracle.com

Conflicts: net/core/net_namespace.c

* rtnl_valid_dump_net_req() has a very minimal implementation in 4.14, hence only a simple substituting of spin_{lock,unlock}_bh() with rcu_spin_{lock,unlock}() was required --- net/core/net_namespace.c | 18 ++++++++++-------- 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c index 1af25d5..37f4313 100644 --- a/net/core/net_namespace.c +++ b/net/core/net_namespace.c @@ -181,9 +181,9 @@ static int net_eq_idr(int id, void *net, void *peer) return 0; }

-/* Should be called with nsid_lock held. If a new id is assigned, the bool alloc - * is set to true, thus the caller knows that the new id must be notified via - * rtnl. +/* Must be called from RCU-critical section or with nsid_lock held. If + * a new id is assigned, the bool alloc is set to true, thus the + * caller knows that the new id must be notified via rtnl. */ static int __peernet2id_alloc(struct net *net, struct net *peer, bool *alloc) { @@ -207,7 +207,7 @@ static int __peernet2id_alloc(struct net *net, struct net *peer, bool *alloc) return NETNSA_NSID_NOT_ASSIGNED; }

-/* should be called with nsid_lock held */ +/* Must be called from RCU-critical section or with nsid_lock held */ static int __peernet2id(struct net *net, struct net *peer) { bool no = false; @@ -240,9 +240,10 @@ int peernet2id(struct net *net, struct net *peer) { int id;

- spin_lock_bh(&net->nsid_lock); + rcu_read_lock(); id = __peernet2id(net, peer); - spin_unlock_bh(&net->nsid_lock); + rcu_read_unlock(); + return id; } EXPORT_SYMBOL(peernet2id); @@ -761,6 +762,7 @@ struct rtnl_net_dump_cb { int s_idx; };

+/* Runs in RCU-critical section. */ static int rtnl_net_dumpid_one(int id, void *peer, void *data) { struct rtnl_net_dump_cb *net_cb = (struct rtnl_net_dump_cb *)data; @@ -791,9 +793,9 @@ static int rtnl_net_dumpid(struct sk_buff *skb, struct netlink_callback *cb) .s_idx = cb->args[0], };

- spin_lock_bh(&net->nsid_lock); + rcu_read_lock(); idr_for_each(&net->netns_ids, rtnl_net_dumpid_one, &net_cb); - spin_unlock_bh(&net->nsid_lock); + rcu_read_unlock();

cb->args[0] = net_cb.idx; return skb->len;