On 11/29/2017 06:48 PM, Tommi Rantala wrote:
> Remove the second tipc_rcv() call in tipc_udp_recv(). We have just
> checked that the bearer is not up, and calling tipc_rcv() with a bearer
> that is not up leads to a TIPC div-by-zero crash in
> tipc_node_calculate_timer(). The crash is rare in practice, but can
> happen like this:
In my opinion, the real root cause of the issue is because we too early
set a not-yet-initialized bearer instance to ub->bearer through
rcu_assign_pointer(ub->bearer, b) in tipc_udp_enable(). Instead if we
assign the bearer pointer at the end of tipc_udp_enable() where the
bearer has been completed the initialization, the issue would be avoided.
Thanks,
Ying
>
> We're enabling a bearer, but it's not yet up and fully initialized.
> At the same time we receive a discovery packet, and in tipc_udp_recv()
> we end up calling tipc_rcv() with the not-yet-initialized bearer,
> causing later the div-by-zero crash in tipc_node_calculate_timer().
>
> Jon Maloy explains the impact of removing the second tipc_rcv() call:
> "link setup in the worst case will be delayed until the next arriving
> discovery messages, 1 sec later, and this is an acceptable delay."
>
> As the tipc_rcv() call is removed, just leave the function via the
> rcu_out label, so that we will kfree_skb().
>
> [ 12.590450] Own node address <1.1.1>, network identity 1
> [ 12.668088] divide error: 0000 [#1] SMP
> [ 12.676952] CPU: 2 PID: 0 Comm: swapper/2 Not tainted 4.14.2-dirty #1
> [ 12.679225] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
> 1.10.2-2.fc27 04/01/2014
> [ 12.682095] task: ffff8c2a761edb80 task.stack: ffffa41cc0cac000
> [ 12.684087] RIP: 0010:tipc_node_calculate_timer.isra.12+0x45/0x60 [tipc]
> [ 12.686486] RSP: 0018:ffff8c2a7fc838a0 EFLAGS: 00010246
> [ 12.688451] RAX: 0000000000000000 RBX: ffff8c2a5b382600 RCX:
> 0000000000000000
> [ 12.691197] RDX: 0000000000000000 RSI: ffff8c2a5b382600 RDI:
> ffff8c2a5b382600
> [ 12.693945] RBP: ffff8c2a7fc838b0 R08: 0000000000000001 R09:
> 0000000000000001
> [ 12.696632] R10: 0000000000000000 R11: 0000000000000000 R12:
> ffff8c2a5d8949d8
> [ 12.699491] R13: ffffffff95ede400 R14: 0000000000000000 R15:
> ffff8c2a5d894800
> [ 12.702338] FS: 0000000000000000(0000) GS:ffff8c2a7fc80000(0000)
> knlGS:0000000000000000
> [ 12.705099] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 12.706776] CR2: 0000000001bb9440 CR3: 00000000bd009001 CR4:
> 00000000003606e0
> [ 12.708847] DR0: 0000000000000000 DR1: 0000000000000000 DR2:
> 0000000000000000
> [ 12.711016] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7:
> 0000000000000400
> [ 12.712627] Call Trace:
> [ 12.713390] <IRQ>
> [ 12.714011] tipc_node_check_dest+0x2e8/0x350 [tipc]
> [ 12.715286] tipc_disc_rcv+0x14d/0x1d0 [tipc]
> [ 12.716370] tipc_rcv+0x8b0/0xd40 [tipc]
> [ 12.717396] ? minmax_running_min+0x2f/0x60
> [ 12.718248] ? dst_alloc+0x4c/0xa0
> [ 12.718964] ? tcp_ack+0xaf1/0x10b0
> [ 12.719658] ? tipc_udp_is_known_peer+0xa0/0xa0 [tipc]
> [ 12.720634] tipc_udp_recv+0x71/0x1d0 [tipc]
> [ 12.721459] ? dst_alloc+0x4c/0xa0
> [ 12.722130] udp_queue_rcv_skb+0x264/0x490
> [ 12.722924] __udp4_lib_rcv+0x21e/0x990
> [ 12.723670] ? ip_route_input_rcu+0x2dd/0xbf0
> [ 12.724442] ? tcp_v4_rcv+0x958/0xa40
> [ 12.725039] udp_rcv+0x1a/0x20
> [ 12.725587] ip_local_deliver_finish+0x97/0x1d0
> [ 12.726323] ip_local_deliver+0xaf/0xc0
> [ 12.726959] ? ip_route_input_noref+0x19/0x20
> [ 12.727689] ip_rcv_finish+0xdd/0x3b0
> [ 12.728307] ip_rcv+0x2ac/0x360
> [ 12.728839] __netif_receive_skb_core+0x6fb/0xa90
> [ 12.729580] ? udp4_gro_receive+0x1a7/0x2c0
> [ 12.730274] __netif_receive_skb+0x1d/0x60
> [ 12.730953] ? __netif_receive_skb+0x1d/0x60
> [ 12.731637] netif_receive_skb_internal+0x37/0xd0
> [ 12.732371] napi_gro_receive+0xc7/0xf0
> [ 12.732920] receive_buf+0x3c3/0xd40
> [ 12.733441] virtnet_poll+0xb1/0x250
> [ 12.733944] net_rx_action+0x23e/0x370
> [ 12.734476] __do_softirq+0xc5/0x2f8
> [ 12.734922] irq_exit+0xfa/0x100
> [ 12.735315] do_IRQ+0x4f/0xd0
> [ 12.735680] common_interrupt+0xa2/0xa2
> [ 12.736126] </IRQ>
> [ 12.736416] RIP: 0010:native_safe_halt+0x6/0x10
> [ 12.736925] RSP: 0018:ffffa41cc0cafe90 EFLAGS: 00000246 ORIG_RAX:
> ffffffffffffff4d
> [ 12.737756] RAX: 0000000000000000 RBX: ffff8c2a761edb80 RCX:
> 0000000000000000
> [ 12.738504] RDX: 0000000000000000 RSI: 0000000000000000 RDI:
> 0000000000000000
> [ 12.739258] RBP: ffffa41cc0cafe90 R08: 0000014b5b9795e5 R09:
> ffffa41cc12c7e88
> [ 12.740118] R10: 0000000000000000 R11: 0000000000000000 R12:
> 0000000000000002
> [ 12.740964] R13: ffff8c2a761edb80 R14: 0000000000000000 R15:
> 0000000000000000
> [ 12.741831] default_idle+0x2a/0x100
> [ 12.742323] arch_cpu_idle+0xf/0x20
> [ 12.742796] default_idle_call+0x28/0x40
> [ 12.743312] do_idle+0x179/0x1f0
> [ 12.743761] cpu_startup_entry+0x1d/0x20
> [ 12.744291] start_secondary+0x112/0x120
> [ 12.744816] secondary_startup_64+0xa5/0xa5
> [ 12.745367] Code: b9 f4 01 00 00 48 89 c2 48 c1 ea 02 48 3d d3 07 00
> 00 48 0f 47 d1 49 8b 0c 24 48 39 d1 76 07 49 89 14 24 48 89 d1 31 d2 48
> 89 df <48> f7 f1 89 c6 e8 81 6e ff ff 5b 41 5c 5d c3 66 90 66 2e 0f 1f
> [ 12.747527] RIP: tipc_node_calculate_timer.isra.12+0x45/0x60 [tipc] RSP:
> ffff8c2a7fc838a0
> [ 12.748555] ---[ end trace 1399ab83390650fd ]---
> [ 12.749296] Kernel panic - not syncing: Fatal exception in interrupt
> [ 12.750123] Kernel Offset: 0x13200000 from 0xffffffff82000000
> (relocation range: 0xffffffff80000000-0xffffffffbfffffff)
> [ 12.751215] Rebooting in 60 seconds..
>
> Fixes: c9b64d492b1f ("tipc: add replicast peer discovery")
> Signed-off-by: Tommi Rantala <tommi.t.rant...@nokia.com>
> Cc: Jon Maloy <jon.ma...@ericsson.com>
> ---
>
> v2: Resorted to a minimal fix, as per feedback from David M.
>
> net/tipc/udp_media.c | 4 ----
> 1 file changed, 4 deletions(-)
>
> diff --git a/net/tipc/udp_media.c b/net/tipc/udp_media.c
> index ecca64fc6a6f..3deabcab4882 100644
> --- a/net/tipc/udp_media.c
> +++ b/net/tipc/udp_media.c
> @@ -371,10 +371,6 @@ static int tipc_udp_recv(struct sock *sk, struct sk_buff
> *skb)
> goto rcu_out;
> }
>
> - tipc_rcv(sock_net(sk), skb, b);
> - rcu_read_unlock();
> - return 0;
> -
> rcu_out:
> rcu_read_unlock();
> out:
>
