Message-ID: <CAEP_g=95s37umz-hLGH0-sB32RcW+t+1dJ=_Eg1jMt4HYG+gEg@mail.gmail.com>
Date:	Fri, 7 Nov 2014 10:34:56 -0800
From:	Jesse Gross <jesse@...ira.com>
To:	Pravin Shelar <pshelar@...ira.com>
Cc:	Jay Vosburgh <jay.vosburgh@...onical.com>,
	netdev <netdev@...r.kernel.org>,
	"discuss@...nvswitch.org" <discuss@...nvswitch.org>
Subject: Re: kernel panic receiving flooded VXLAN traffic with OVS

On Fri, Nov 7, 2014 at 9:40 AM, Pravin Shelar <pshelar@...ira.com> wrote:
> On Thu, Nov 6, 2014 at 5:58 PM, Jay Vosburgh <jay.vosburgh@...onical.com> wrote:
>>
>>         I am able to reproduce a kernel panic on an system using
>> openvswitch when receiving VXLAN traffic under a very specific set of
>> circumstances.  This occurs with a recent net-next as well as an Ubuntu
>> 3.13 kernel.  I'm not sure if the error lies in OVS, GRO, or elsewhere.
>>
>>         In summary, when the system receives multiple VXLAN encapsulated
>> TCP segments for a different system (not intended for local reception)
>> that are from the middle of an active connection (received due to a switch
>> flood), and are tagged to a VLAN not configured on the local host, then
>> the system panics in skb_segment when OVS calls __skb_gso_segment on the
>> GRO skb prior to performing an upcall to user space.
>>
>>         The panic occurs in skbuff.c:skb_segment(), at the BUG_ON around
>> line 3036:
>>
>> struct sk_buff *skb_segment(struct sk_buff *head_skb,
>>                             netdev_features_t features)
>> {
>> [...]
>>                 skb_shinfo(nskb)->tx_flags = skb_shinfo(head_skb)->tx_flags &
>>                         SKBTX_SHARED_FRAG;
>>
>>                 while (pos < offset + len) {
>>                         if (i >= nfrags) {
>>                                 BUG_ON(skb_headlen(list_skb));
>>
>>                                 i = 0;
>>
>>
>>         The BUG_ON triggers because the skbs that have been GRO
>> accumulated are partially or entirely linear, depending upon the receiving
>> network device (sky2 is partial, enic is entire).  The receive buffers end
>> up being linear evidently because the mtu is set to 9000, and
>> __netdev_alloc_skb calls __alloc_skb (and thus kmalloc) instead of
>> __netdev_alloc_frag followed by build_skb.
>>
>>         The foreign-VLAN VXLAN TCP segments are not processed as normal
>> VXLAN traffic, as there is no listener on the VLAN in question, so once
>> GRO processes them, they are sent directly to ovs_vport_receive.  The
>> panic stack appears as follows:
>>
>> [ 6558.812214] kernel BUG at net/core/skbuff.c:3025!
>> [ 6558.812214] invalid opcode: 0000 [#1] SMP
>> [ 6558.812214] Modules linked in: veth 8021q garp mrp bonding xt_tcpudp bridge stp llc iptable_filter ip_tables x_tables openvswitch vxlan ip6_udp_tunnel udp_tunnel gre libcrc32c i915 video drm_kms_helper coretemp drm kvm_intel kvm gpio_ich ppdev parport_pc lp lpc_ich serio_raw i2c_algo_bit parport mac_hid hid_generic usbhid hid psmouse r8169 mii sky2
>> [ 6558.812214] CPU: 0 PID: 3 Comm: ksoftirqd/0 Not tainted 3.17.0-rc7-testola+ #5
>> [ 6558.812214] Hardware name: LENOVO 0829F3U/To be filled by O.E.M., BIOS 90KT15AUS 07/21/2010
>> [ 6558.812214] task: ffff880139eb3200 ti: ffff880139ed0000 task.ti: ffff880139ed0000
>> [ 6558.812214] RIP: 0010:[<ffffffff81616bc2>]  [<ffffffff81616bc2>] skb_segment+0x9d2/0xa00
>> [ 6558.812214] RSP: 0018:ffff880139ed3610  EFLAGS: 00010216
>> [ 6558.812214] RAX: 00000000000002dc RBX: ffff8800a3be5e00 RCX: ffff8800b10a26f0
>> [ 6558.812214] RDX: 0000000000000074 RSI: ffff8800b10a2600 RDI: ffff8800b10a2000
>> [ 6558.812214] RBP: ffff880139ed36e0 R08: 0000000000000022 R09: 0000000000000000
>> [ 6558.812214] R10: ffff8800b11e6000 R11: 00000000000005ca R12: ffff8800b10a20f0
>> [ 6558.812214] R13: 0000000000000000 R14: ffff8800b116cb00 R15: 0000000000000074
>> [ 6558.812214] FS:  0000000000000000(0000) GS:ffff88013fc00000(0000) knlGS:0000000000000000
>> [ 6558.812214] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
>> [ 6558.812214] CR2: 00007fa906f4f148 CR3: 00000000b2a46000 CR4: 00000000000407f0
>> [ 6558.812214] Stack:
>> [ 6558.812214]  00000000000016a0 ffff880031353800 ffffffffffffffde ffff8800000005ca
>> [ 6558.812214]  0000000000000022 0000000000000040 ffff8800b11e6000 00000001000016a0
>> [ 6558.812214]  0000000000000000 0000000000000022 00000000000005a8 ffff8800a3be5e00
>> [ 6558.812214] Call Trace:
>> [ 6558.812214]  [<ffffffff8168c97f>] udp4_ufo_fragment+0x10f/0x1a0
>> [ 6558.812214]  [<ffffffff81695c51>] inet_gso_segment+0x141/0x370
>> [ 6558.812214]  [<ffffffff810aa2c8>] ? __wake_up_common+0x58/0x90
>> [ 6558.812214]  [<ffffffff81624f4f>] skb_mac_gso_segment+0x9f/0x100
>> [ 6558.812214]  [<ffffffff81625016>] __skb_gso_segment+0x66/0xd0
>> [ 6558.812214]  [<ffffffffa01d4c91>] queue_gso_packets+0x41/0x130 [openvswitch]
>> [ 6558.812214]  [<ffffffff8121aa4d>] ? ep_poll_safewake+0x2d/0x30
>> [ 6558.812214]  [<ffffffff8121b03d>] ? ep_poll_callback+0xcd/0x170
>> [ 6558.812214]  [<ffffffff810aa2c8>] ? __wake_up_common+0x58/0x90
>> [ 6558.812214]  [<ffffffff810aa860>] ? __wake_up_sync_key+0x50/0x60
>> [ 6558.812214]  [<ffffffff8161c232>] ? __skb_flow_dissect+0x162/0x4c0
>> [ 6558.812214]  [<ffffffff8172001f>] ? __slab_free+0xfe/0x2c3
>> [ 6558.812214]  [<ffffffff816107af>] ? kfree_skbmem+0x3f/0xa0
>> [ 6558.812214]  [<ffffffff8161c5ba>] ? __skb_get_hash+0x2a/0x160
>> [ 6558.812214]  [<ffffffffa01d609e>] ovs_dp_upcall+0x2e/0x70 [openvswitch]
>> [ 6558.812214]  [<ffffffffa01d6193>] ovs_dp_process_packet+0xb3/0xd0 [openvswitch]
>> [ 6558.812214]  [<ffffffffa01dc860>] ovs_vport_receive+0x60/0x80 [openvswitch]
>> [ 6558.812214]  [<ffffffff811828f1>] ? zone_statistics+0x81/0xa0
>> [ 6558.812214]  [<ffffffff81617819>] ? skb_gro_receive+0x559/0x5f0
>> [ 6558.812214]  [<ffffffff81695ada>] ? inet_gro_receive+0x1da/0x210
>> [ 6558.812214]  [<ffffffffa01dd10a>] netdev_frame_hook+0xca/0x130 [openvswitch]
>> [ 6558.812214]  [<ffffffff816233aa>] __netif_receive_skb_core+0x1ba/0x7a0
>> [ 6558.812214]  [<ffffffff816239a8>] __netif_receive_skb+0x18/0x60
>> [ 6558.812214]  [<ffffffff81623a13>] netif_receive_skb_internal+0x23/0x90
>> [ 6558.812214]  [<ffffffff8168cefa>] ? udp4_gro_complete+0x6a/0x70
>> [ 6558.812214]  [<ffffffff81623b94>] napi_gro_complete+0xa4/0xe0
>> [ 6558.812214]  [<ffffffff81623c3d>] napi_gro_flush+0x6d/0x90
>> [ 6558.812214]  [<ffffffff81623c7e>] napi_complete+0x1e/0x50
>> [ 6558.812214]  [<ffffffffa0006538>] sky2_poll+0xa38/0xd80 [sky2]
>> [ 6558.812214]  [<ffffffff81623e02>] net_rx_action+0x152/0x250
>> [ 6558.812214]  [<ffffffff81070aa5>] __do_softirq+0xf5/0x2e0
>> [ 6558.812214]  [<ffffffff81070cc0>] run_ksoftirqd+0x30/0x50
>> [ 6558.812214]  [<ffffffff8108e0ff>] smpboot_thread_fn+0xff/0x1b0
>> [ 6558.812214]  [<ffffffff8108e000>] ? SyS_setgroups+0x1a0/0x1a0
>> [ 6558.812214]  [<ffffffff8108a5a2>] kthread+0xd2/0xf0
>> [ 6558.812214]  [<ffffffff8108a4d0>] ? kthread_create_on_node+0x180/0x180
>> [ 6558.812214]  [<ffffffff81729e3c>] ret_from_fork+0x7c/0xb0
>> [ 6558.812214]  [<ffffffff8108a4d0>] ? kthread_create_on_node+0x180/0x180
>> [ 6558.812214] Code: 8b 44 24 70 44 8b 4c 24 30 44 8b 5c 24 18 8b 54 24 08 48 8b 0c 24 0f 85 0f fd ff ff e9 06 fd ff ff 0f 1f 84 00 00 00 00 00 0f 0b <0f> 0b 0f 0b c6 44 24 3b 01 e9 28 f7 ff ff e8 76 db 10 00 0f 0b
>> [ 6558.812214] RIP  [<ffffffff81616bc2>] skb_segment+0x9d2/0xa00
>> [ 6558.812214]  RSP <ffff880139ed3610>
>>
>>         I'm not sure if this is an error on the part of the RX / GRO
>> processing in assembling the GRO skb, or in how OVS calls skb_segment.
>>
>
> I think this is related skb_segment() issue where it is not able to
> handle this type of skb geometry. We need to fix skb-segmentation. I
> will investigate it more.

One problem that I see is that vxlan_gro_complete() doesn't add
SKB_GSO_UDP_TUNNEL to gso_type. This causes us to attempt
fragmentation as UDP rather than continuing down to do TCP
segmentation. That probably screws up the skb geometry.
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