From: Daniel Borkmann daniel@iogearbox.net
commit 4a81f6da9cb2d1ef911131a6fd8bd15cb61fc772 upstream.
syzkaller was able to trigger a deadlock for NTF_MANAGED entries [0]:
kworker/0:16/14617 is trying to acquire lock: ffffffff8d4dd370 (&tbl->lock){++-.}-{2:2}, at: ___neigh_create+0x9e1/0x2990 net/core/neighbour.c:652 [...] but task is already holding lock: ffffffff8d4dd370 (&tbl->lock){++-.}-{2:2}, at: neigh_managed_work+0x35/0x250 net/core/neighbour.c:1572
The neighbor entry turned to NUD_FAILED state, where __neigh_event_send() triggered an immediate probe as per commit cd28ca0a3dd1 ("neigh: reduce arp latency") via neigh_probe() given table lock was held.
One option to fix this situation is to defer the neigh_probe() back to the neigh_timer_handler() similarly as pre cd28ca0a3dd1. For the case of NTF_MANAGED, this deferral is acceptable given this only happens on actual failure state and regular / expected state is NUD_VALID with the entry already present.
The fix adds a parameter to __neigh_event_send() in order to communicate whether immediate probe is allowed or disallowed. Existing call-sites of neigh_event_send() default as-is to immediate probe. However, the neigh_managed_work() disables it via use of neigh_event_send_probe().
[0] <TASK> __dump_stack lib/dump_stack.c:88 [inline] dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106 print_deadlock_bug kernel/locking/lockdep.c:2956 [inline] check_deadlock kernel/locking/lockdep.c:2999 [inline] validate_chain kernel/locking/lockdep.c:3788 [inline] __lock_acquire.cold+0x149/0x3ab kernel/locking/lockdep.c:5027 lock_acquire kernel/locking/lockdep.c:5639 [inline] lock_acquire+0x1ab/0x510 kernel/locking/lockdep.c:5604 __raw_write_lock_bh include/linux/rwlock_api_smp.h:202 [inline] _raw_write_lock_bh+0x2f/0x40 kernel/locking/spinlock.c:334 ___neigh_create+0x9e1/0x2990 net/core/neighbour.c:652 ip6_finish_output2+0x1070/0x14f0 net/ipv6/ip6_output.c:123 __ip6_finish_output net/ipv6/ip6_output.c:191 [inline] __ip6_finish_output+0x61e/0xe90 net/ipv6/ip6_output.c:170 ip6_finish_output+0x32/0x200 net/ipv6/ip6_output.c:201 NF_HOOK_COND include/linux/netfilter.h:296 [inline] ip6_output+0x1e4/0x530 net/ipv6/ip6_output.c:224 dst_output include/net/dst.h:451 [inline] NF_HOOK include/linux/netfilter.h:307 [inline] ndisc_send_skb+0xa99/0x17f0 net/ipv6/ndisc.c:508 ndisc_send_ns+0x3a9/0x840 net/ipv6/ndisc.c:650 ndisc_solicit+0x2cd/0x4f0 net/ipv6/ndisc.c:742 neigh_probe+0xc2/0x110 net/core/neighbour.c:1040 __neigh_event_send+0x37d/0x1570 net/core/neighbour.c:1201 neigh_event_send include/net/neighbour.h:470 [inline] neigh_managed_work+0x162/0x250 net/core/neighbour.c:1574 process_one_work+0x9ac/0x1650 kernel/workqueue.c:2307 worker_thread+0x657/0x1110 kernel/workqueue.c:2454 kthread+0x2e9/0x3a0 kernel/kthread.c:377 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295 </TASK>
Fixes: 7482e3841d52 ("net, neigh: Add NTF_MANAGED flag for managed neighbor entries") Reported-by: syzbot+5239d0e1778a500d477a@syzkaller.appspotmail.com Signed-off-by: Daniel Borkmann daniel@iogearbox.net Cc: Eric Dumazet edumazet@google.com Cc: Roopa Prabhu roopa@nvidia.com Tested-by: syzbot+5239d0e1778a500d477a@syzkaller.appspotmail.com Reviewed-by: David Ahern dsahern@kernel.org Link: https://lore.kernel.org/r/20220201193942.5055-1-daniel@iogearbox.net Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- include/net/neighbour.h | 18 +++++++++++++----- net/core/neighbour.c | 18 ++++++++++++------ 2 files changed, 25 insertions(+), 11 deletions(-)
--- a/include/net/neighbour.h +++ b/include/net/neighbour.h @@ -336,7 +336,8 @@ static inline struct neighbour *neigh_cr return __neigh_create(tbl, pkey, dev, true); } void neigh_destroy(struct neighbour *neigh); -int __neigh_event_send(struct neighbour *neigh, struct sk_buff *skb); +int __neigh_event_send(struct neighbour *neigh, struct sk_buff *skb, + const bool immediate_ok); int neigh_update(struct neighbour *neigh, const u8 *lladdr, u8 new, u32 flags, u32 nlmsg_pid); void __neigh_set_probe_once(struct neighbour *neigh); @@ -446,17 +447,24 @@ static inline struct neighbour * neigh_c
#define neigh_hold(n) refcount_inc(&(n)->refcnt)
-static inline int neigh_event_send(struct neighbour *neigh, struct sk_buff *skb) +static __always_inline int neigh_event_send_probe(struct neighbour *neigh, + struct sk_buff *skb, + const bool immediate_ok) { unsigned long now = jiffies; - + if (READ_ONCE(neigh->used) != now) WRITE_ONCE(neigh->used, now); - if (!(neigh->nud_state&(NUD_CONNECTED|NUD_DELAY|NUD_PROBE))) - return __neigh_event_send(neigh, skb); + if (!(neigh->nud_state & (NUD_CONNECTED | NUD_DELAY | NUD_PROBE))) + return __neigh_event_send(neigh, skb, immediate_ok); return 0; }
+static inline int neigh_event_send(struct neighbour *neigh, struct sk_buff *skb) +{ + return neigh_event_send_probe(neigh, skb, true); +} + #if IS_ENABLED(CONFIG_BRIDGE_NETFILTER) static inline int neigh_hh_bridge(struct hh_cache *hh, struct sk_buff *skb) { --- a/net/core/neighbour.c +++ b/net/core/neighbour.c @@ -1133,7 +1133,8 @@ out: neigh_release(neigh); }
-int __neigh_event_send(struct neighbour *neigh, struct sk_buff *skb) +int __neigh_event_send(struct neighbour *neigh, struct sk_buff *skb, + const bool immediate_ok) { int rc; bool immediate_probe = false; @@ -1154,12 +1155,17 @@ int __neigh_event_send(struct neighbour atomic_set(&neigh->probes, NEIGH_VAR(neigh->parms, UCAST_PROBES)); neigh_del_timer(neigh); - neigh->nud_state = NUD_INCOMPLETE; + neigh->nud_state = NUD_INCOMPLETE; neigh->updated = now; - next = now + max(NEIGH_VAR(neigh->parms, RETRANS_TIME), - HZ/100); + if (!immediate_ok) { + next = now + 1; + } else { + immediate_probe = true; + next = now + max(NEIGH_VAR(neigh->parms, + RETRANS_TIME), + HZ / 100); + } neigh_add_timer(neigh, next); - immediate_probe = true; } else { neigh->nud_state = NUD_FAILED; neigh->updated = jiffies; @@ -1571,7 +1577,7 @@ static void neigh_managed_work(struct wo
write_lock_bh(&tbl->lock); list_for_each_entry(neigh, &tbl->managed_list, managed_list) - neigh_event_send(neigh, NULL); + neigh_event_send_probe(neigh, NULL, false); queue_delayed_work(system_power_efficient_wq, &tbl->managed_work, NEIGH_VAR(&tbl->parms, DELAY_PROBE_TIME)); write_unlock_bh(&tbl->lock);