From a0efb80ce3abacfd22a4284c3730924fc2f1f077 Mon Sep 17 00:00:00 2001 From: WANG Cong Date: Tue, 30 Sep 2014 16:07:24 -0700 Subject: [PATCH] net_sched: avoid calling tcf_unbind_filter() in call_rcu callback This fixes the following crash: [ 63.976822] general protection fault: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC [ 63.980094] CPU: 1 PID: 15 Comm: ksoftirqd/1 Not tainted 3.17.0-rc6+ #648 [ 63.980094] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 [ 63.980094] task: ffff880117dea690 ti: ffff880117dfc000 task.ti: ffff880117dfc000 [ 63.980094] RIP: 0010:[] [] u32_destroy_key+0x27/0x6d [ 63.980094] RSP: 0018:ffff880117dffcc0 EFLAGS: 00010202 [ 63.980094] RAX: ffff880117dea690 RBX: ffff8800d02e0820 RCX: 0000000000000000 [ 63.980094] RDX: 0000000000000001 RSI: 0000000000000002 RDI: 6b6b6b6b6b6b6b6b [ 63.980094] RBP: ffff880117dffcd0 R08: 0000000000000000 R09: 0000000000000000 [ 63.980094] R10: 00006c0900006ba8 R11: 00006ba100006b9d R12: 0000000000000001 [ 63.980094] R13: ffff8800d02e0898 R14: ffffffff817e6d4d R15: ffff880117387a30 [ 63.980094] FS: 0000000000000000(0000) GS:ffff88011a800000(0000) knlGS:0000000000000000 [ 63.980094] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b [ 63.980094] CR2: 00007f07e6732fed CR3: 000000011665b000 CR4: 00000000000006e0 [ 63.980094] Stack: [ 63.980094] ffff88011a9cd300 ffffffff82051ac0 ffff880117dffce0 ffffffff817e6d68 [ 63.980094] ffff880117dffd70 ffffffff810cb4c7 ffffffff810cb3cd ffff880117dfffd8 [ 63.980094] ffff880117dea690 ffff880117dea690 ffff880117dfffd8 000000000000000a [ 63.980094] Call Trace: [ 63.980094] [] u32_delete_key_freepf_rcu+0x1b/0x1d [ 63.980094] [] rcu_process_callbacks+0x3bb/0x691 [ 63.980094] [] ? rcu_process_callbacks+0x2c1/0x691 [ 63.980094] [] ? u32_destroy_key+0x6d/0x6d [ 63.980094] [] __do_softirq+0x142/0x323 [ 63.980094] [] run_ksoftirqd+0x23/0x53 [ 63.980094] [] smpboot_thread_fn+0x203/0x221 [ 63.980094] [] ? smpboot_unpark_thread+0x33/0x33 [ 63.980094] [] kthread+0xc9/0xd1 [ 63.980094] [] ? do_wait_for_common+0xf8/0x125 [ 63.980094] [] ? __kthread_parkme+0x61/0x61 [ 63.980094] [] ret_from_fork+0x7c/0xb0 [ 63.980094] [] ? __kthread_parkme+0x61/0x61 tp could be freed in call_rcu callback too, the order is not guaranteed. John Fastabend says: ==================== Its worth noting why this is safe. Any running schedulers will either read the valid class field or it will be zeroed. All schedulers today when the class is 0 do a lookup using the same call used by the tcf_exts_bind(). So even if we have a running classifier hit the null class pointer it will do a lookup and get to the same result. This is particularly fragile at the moment because the only way to verify this is to audit the schedulers call sites. ==================== Cc: John Fastabend Signed-off-by: Cong Wang Acked-by: John Fastabend Signed-off-by: David S. Miller --- include/net/pkt_cls.h | 6 +----- net/sched/cls_u32.c | 10 ++++++---- 2 files changed, 7 insertions(+), 9 deletions(-) diff --git a/include/net/pkt_cls.h b/include/net/pkt_cls.h index 73f9532ee581..ef44ad9a6426 100644 --- a/include/net/pkt_cls.h +++ b/include/net/pkt_cls.h @@ -20,11 +20,7 @@ int unregister_tcf_proto_ops(struct tcf_proto_ops *ops); static inline unsigned long __cls_set_class(unsigned long *clp, unsigned long cl) { - unsigned long old_cl; - - old_cl = *clp; - *clp = cl; - return old_cl; + return xchg(clp, cl); } static inline unsigned long diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c index 4be3ebf46d67..0472909bb014 100644 --- a/net/sched/cls_u32.c +++ b/net/sched/cls_u32.c @@ -358,7 +358,6 @@ static int u32_destroy_key(struct tcf_proto *tp, struct tc_u_knode *n, bool free_pf) { - tcf_unbind_filter(tp, &n->res); tcf_exts_destroy(&n->exts); if (n->ht_down) n->ht_down->refcnt--; @@ -416,6 +415,7 @@ static int u32_delete_key(struct tcf_proto *tp, struct tc_u_knode *key) if (pkp == key) { RCU_INIT_POINTER(*kp, key->next); + tcf_unbind_filter(tp, &key->res); call_rcu(&key->rcu, u32_delete_key_freepf_rcu); return 0; } @@ -425,7 +425,7 @@ static int u32_delete_key(struct tcf_proto *tp, struct tc_u_knode *key) return 0; } -static void u32_clear_hnode(struct tc_u_hnode *ht) +static void u32_clear_hnode(struct tcf_proto *tp, struct tc_u_hnode *ht) { struct tc_u_knode *n; unsigned int h; @@ -434,6 +434,7 @@ static void u32_clear_hnode(struct tc_u_hnode *ht) while ((n = rtnl_dereference(ht->ht[h])) != NULL) { RCU_INIT_POINTER(ht->ht[h], rtnl_dereference(n->next)); + tcf_unbind_filter(tp, &n->res); call_rcu(&n->rcu, u32_delete_key_freepf_rcu); } } @@ -447,7 +448,7 @@ static int u32_destroy_hnode(struct tcf_proto *tp, struct tc_u_hnode *ht) WARN_ON(ht->refcnt); - u32_clear_hnode(ht); + u32_clear_hnode(tp, ht); hn = &tp_c->hlist; for (phn = rtnl_dereference(*hn); @@ -482,7 +483,7 @@ static void u32_destroy(struct tcf_proto *tp) ht; ht = rtnl_dereference(ht->next)) { ht->refcnt--; - u32_clear_hnode(ht); + u32_clear_hnode(tp, ht); } while ((ht = rtnl_dereference(tp_c->hlist)) != NULL) { @@ -731,6 +732,7 @@ static int u32_change(struct net *net, struct sk_buff *in_skb, } u32_replace_knode(tp, tp_c, new); + tcf_unbind_filter(tp, &n->res); call_rcu(&n->rcu, u32_delete_key_rcu); return 0; } -- 2.20.1