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Subject[PATCH 3.12 52/88] mac80211: mesh: flush mesh paths unconditionally
Date
From: Bob Copeland <me@bobcopeland.com>

3.12-stable review patch. If anyone has any objections, please let me know.

===============

commit fe7a7c57629e8dcbc0e297363a9b2366d67a6dc5 upstream.

Currently, the mesh paths associated with a nexthop station are cleaned
up in the following code path:

__sta_info_destroy_part1
synchronize_net()
__sta_info_destroy_part2
-> cleanup_single_sta
-> mesh_sta_cleanup
-> mesh_plink_deactivate
-> mesh_path_flush_by_nexthop

However, there are a couple of problems here:

1) the paths aren't flushed at all if the MPM is running in userspace
(e.g. when using wpa_supplicant or authsae)

2) there is no synchronize_rcu between removing the path and readers
accessing the nexthop, which means the following race is possible:

CPU0 CPU1
~~~~ ~~~~
sta_info_destroy_part1()
synchronize_net()
rcu_read_lock()
mesh_nexthop_resolve()
mpath = mesh_path_lookup()
[...] -> mesh_path_flush_by_nexthop()
sta = rcu_dereference(
mpath->next_hop)
kfree(sta)
access sta <-- CRASH

Fix both of these by unconditionally flushing paths before destroying
the sta, and by adding a synchronize_net() after path flush to ensure
no active readers can still dereference the sta.

Fixes this crash:

[ 348.529295] BUG: unable to handle kernel paging request at 00020040
[ 348.530014] IP: [<f929245d>] ieee80211_mps_set_frame_flags+0x40/0xaa [mac80211]
[ 348.530014] *pde = 00000000
[ 348.530014] Oops: 0000 [#1] PREEMPT
[ 348.530014] Modules linked in: drbg ansi_cprng ctr ccm ppp_generic slhc ipt_MASQUERADE nf_nat_masquerade_ipv4 8021q ]
[ 348.530014] CPU: 0 PID: 20597 Comm: wget Tainted: G O 4.6.0-rc5-wt=V1 #1
[ 348.530014] Hardware name: To Be Filled By O.E.M./To be filled by O.E.M., BIOS 080016 11/07/2014
[ 348.530014] task: f64fa280 ti: f4f9c000 task.ti: f4f9c000
[ 348.530014] EIP: 0060:[<f929245d>] EFLAGS: 00010246 CPU: 0
[ 348.530014] EIP is at ieee80211_mps_set_frame_flags+0x40/0xaa [mac80211]
[ 348.530014] EAX: f4ce63e0 EBX: 00000088 ECX: f3788416 EDX: 00020008
[ 348.530014] ESI: 00000000 EDI: 00000088 EBP: f6409a4c ESP: f6409a40
[ 348.530014] DS: 007b ES: 007b FS: 0000 GS: 0033 SS: 0068
[ 348.530014] CR0: 80050033 CR2: 00020040 CR3: 33190000 CR4: 00000690
[ 348.530014] Stack:
[ 348.530014] 00000000 f4ce63e0 f5f9bd80 f6409a64 f9291d80 0000ce67 f5d51e00 f4ce63e0
[ 348.530014] f3788416 f6409a80 f9291dc1 f4ce8320 f4ce63e0 f5d51e00 f4ce63e0 f4ce8320
[ 348.530014] f6409a98 f9277f6f 00000000 00000000 0000007c 00000000 f6409b2c f9278dd1
[ 348.530014] Call Trace:
[ 348.530014] [<f9291d80>] mesh_nexthop_lookup+0xbb/0xc8 [mac80211]
[ 348.530014] [<f9291dc1>] mesh_nexthop_resolve+0x34/0xd8 [mac80211]
[ 348.530014] [<f9277f6f>] ieee80211_xmit+0x92/0xc1 [mac80211]
[ 348.530014] [<f9278dd1>] __ieee80211_subif_start_xmit+0x807/0x83c [mac80211]
[ 348.530014] [<c04df012>] ? sch_direct_xmit+0xd7/0x1b3
[ 348.530014] [<c022a8c6>] ? __local_bh_enable_ip+0x5d/0x7b
[ 348.530014] [<f956870c>] ? nf_nat_ipv4_out+0x4c/0xd0 [nf_nat_ipv4]
[ 348.530014] [<f957e036>] ? iptable_nat_ipv4_fn+0xf/0xf [iptable_nat]
[ 348.530014] [<c04c6f45>] ? netif_skb_features+0x14d/0x30a
[ 348.530014] [<f9278e10>] ieee80211_subif_start_xmit+0xa/0xe [mac80211]
[ 348.530014] [<c04c769c>] dev_hard_start_xmit+0x1f8/0x267
[ 348.530014] [<c04c7261>] ? validate_xmit_skb.isra.120.part.121+0x10/0x253
[ 348.530014] [<c04defc6>] sch_direct_xmit+0x8b/0x1b3
[ 348.530014] [<c04c7a9c>] __dev_queue_xmit+0x2c8/0x513
[ 348.530014] [<c04c7cfb>] dev_queue_xmit+0xa/0xc
[ 348.530014] [<f91bfc7a>] batadv_send_skb_packet+0xd6/0xec [batman_adv]
[ 348.530014] [<f91bfdc4>] batadv_send_unicast_skb+0x15/0x4a [batman_adv]
[ 348.530014] [<f91b5938>] batadv_dat_send_data+0x27e/0x310 [batman_adv]
[ 348.530014] [<f91c30b5>] ? batadv_tt_global_hash_find.isra.11+0x8/0xa [batman_adv]
[ 348.530014] [<f91b63f3>] batadv_dat_snoop_outgoing_arp_request+0x208/0x23d [batman_adv]
[ 348.530014] [<f91c0cd9>] batadv_interface_tx+0x206/0x385 [batman_adv]
[ 348.530014] [<c04c769c>] dev_hard_start_xmit+0x1f8/0x267
[ 348.530014] [<c04c7261>] ? validate_xmit_skb.isra.120.part.121+0x10/0x253
[ 348.530014] [<c04defc6>] sch_direct_xmit+0x8b/0x1b3
[ 348.530014] [<c04c7a9c>] __dev_queue_xmit+0x2c8/0x513
[ 348.530014] [<f80cbd2a>] ? igb_xmit_frame+0x57/0x72 [igb]
[ 348.530014] [<c04c7cfb>] dev_queue_xmit+0xa/0xc
[ 348.530014] [<f843a326>] br_dev_queue_push_xmit+0xeb/0xfb [bridge]
[ 348.530014] [<f843a35f>] br_forward_finish+0x29/0x74 [bridge]
[ 348.530014] [<f843a23b>] ? deliver_clone+0x3b/0x3b [bridge]
[ 348.530014] [<f843a714>] __br_forward+0x89/0xe7 [bridge]
[ 348.530014] [<f843a336>] ? br_dev_queue_push_xmit+0xfb/0xfb [bridge]
[ 348.530014] [<f843a234>] deliver_clone+0x34/0x3b [bridge]
[ 348.530014] [<f843a68b>] ? br_flood+0x95/0x95 [bridge]
[ 348.530014] [<f843a66d>] br_flood+0x77/0x95 [bridge]
[ 348.530014] [<f843a809>] br_flood_forward+0x13/0x1a [bridge]
[ 348.530014] [<f843a68b>] ? br_flood+0x95/0x95 [bridge]
[ 348.530014] [<f843b877>] br_handle_frame_finish+0x392/0x3db [bridge]
[ 348.530014] [<c04e9b2b>] ? nf_iterate+0x2b/0x6b
[ 348.530014] [<f843baa6>] br_handle_frame+0x1e6/0x240 [bridge]
[ 348.530014] [<f843b4e5>] ? br_handle_local_finish+0x6a/0x6a [bridge]
[ 348.530014] [<c04c4ba0>] __netif_receive_skb_core+0x43a/0x66b
[ 348.530014] [<f843b8c0>] ? br_handle_frame_finish+0x3db/0x3db [bridge]
[ 348.530014] [<c023cea4>] ? resched_curr+0x19/0x37
[ 348.530014] [<c0240707>] ? check_preempt_wakeup+0xbf/0xfe
[ 348.530014] [<c0255dec>] ? ktime_get_with_offset+0x5c/0xfc
[ 348.530014] [<c04c4fc1>] __netif_receive_skb+0x47/0x55
[ 348.530014] [<c04c57ba>] netif_receive_skb_internal+0x40/0x5a
[ 348.530014] [<c04c61ef>] napi_gro_receive+0x3a/0x94
[ 348.530014] [<f80ce8d5>] igb_poll+0x6fd/0x9ad [igb]
[ 348.530014] [<c0242bd8>] ? swake_up_locked+0x14/0x26
[ 348.530014] [<c04c5d29>] net_rx_action+0xde/0x250
[ 348.530014] [<c022a743>] __do_softirq+0x8a/0x163
[ 348.530014] [<c022a6b9>] ? __hrtimer_tasklet_trampoline+0x19/0x19
[ 348.530014] [<c021100f>] do_softirq_own_stack+0x26/0x2c
[ 348.530014] <IRQ>
[ 348.530014] [<c022a957>] irq_exit+0x31/0x6f
[ 348.530014] [<c0210eb2>] do_IRQ+0x8d/0xa0
[ 348.530014] [<c058152c>] common_interrupt+0x2c/0x40
[ 348.530014] Code: e7 8c 00 66 81 ff 88 00 75 12 85 d2 75 0e b2 c3 b8 83 e9 29 f9 e8 a7 5f f9 c6 eb 74 66 81 e3 8c 005
[ 348.530014] EIP: [<f929245d>] ieee80211_mps_set_frame_flags+0x40/0xaa [mac80211] SS:ESP 0068:f6409a40
[ 348.530014] CR2: 0000000000020040
[ 348.530014] ---[ end trace 48556ac26779732e ]---
[ 348.530014] Kernel panic - not syncing: Fatal exception in interrupt
[ 348.530014] Kernel Offset: disabled

Reported-by: Fred Veldini <fred.veldini@gmail.com>
Tested-by: Fred Veldini <fred.veldini@gmail.com>
Signed-off-by: Bob Copeland <me@bobcopeland.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
net/mac80211/mesh.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/net/mac80211/mesh.c b/net/mac80211/mesh.c
index 707ac61d63e5..67559f7a7832 100644
--- a/net/mac80211/mesh.c
+++ b/net/mac80211/mesh.c
@@ -160,6 +160,10 @@ void mesh_sta_cleanup(struct sta_info *sta)
del_timer_sync(&sta->plink_timer);
}

+ /* make sure no readers can access nexthop sta from here on */
+ mesh_path_flush_by_nexthop(sta);
+ synchronize_net();
+
if (changed)
ieee80211_mbss_info_change_notify(sdata, changed);
}
--
2.9.1
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