From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: Re: skb_under_panic in ip_tunnel_xmit Date: Wed, 02 Mar 2016 10:14:49 -0800 Message-ID: <1456942489.648.113.camel@edumazet-ThinkPad-T530> References: <20160302171159.8A27C384B80@fruggeri-Arora18.sjc.aristanetworks.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, frugger@arista.com To: Francesco Ruggeri Return-path: Received: from mail-pa0-f51.google.com ([209.85.220.51]:35790 "EHLO mail-pa0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751793AbcCBSOw (ORCPT ); Wed, 2 Mar 2016 13:14:52 -0500 Received: by mail-pa0-f51.google.com with SMTP id bj10so68028661pad.2 for ; Wed, 02 Mar 2016 10:14:51 -0800 (PST) In-Reply-To: <20160302171159.8A27C384B80@fruggeri-Arora18.sjc.aristanetworks.com> Sender: netdev-owner@vger.kernel.org List-ID: On mer., 2016-03-02 at 09:11 -0800, Francesco Ruggeri wrote: > I can consistently get this panic on 4.4.1 as well as 3.18. > > [ 2076.264975] gre: GRE over IPv4 demultiplexor driver > [ 2076.269326] ip_gre: GRE over IPv4 tunneling driver > [ 2076.274464] conntrack: generic helper won't handle protocol 47. Please consider loading the specific helper module. > [ 2088.868553] skbuff: skb_under_panic: text:ffffffff814c03f2 len:108 put:20 head:ffff8800a5f6c400 data:ffff8800a5f6c3f8 tail:0x64 end:0xc0 dev:t3 > [ 2088.869755] ------------[ cut here ]------------ > [ 2088.870179] kernel BUG at net/core/skbuff.c:102! > [ 2088.870599] invalid opcode: 0000 [#1] SMP > [ 2088.871024] Modules linked in: ip_gre ip_tunnel gre dummy iptable_filter rfcomm bnep macvlan snd_seq_midi snd_seq_midi_event btusb btrtl btbcm btintel sg bluetooth joydev snd_ens1371 snd_ac97_codec ac97_bus coretemp hwmon snd_seq snd_pcm snd_timer snd_rawmidi snd_seq_device snd ppdev soundcore ip6table_filter ip6_tables bonding gameport serio_raw pcspkr battery kvm parport_pc nfsd auth_rpcgss oid_registry parport irqbypass ac irda crc_ccitt fuse nfs_acl lockd xt_multiport acpi_cpufreq tpm_tis tpm iptable_nat shpchp grace nf_conntrack_ipv4 nf_defrag_ipv4 i2c_piix4 nf_nat_ipv4 ip_tables nf_nat nf_conntrack x_tables tun 8021q uinput vmwgfx crc32c_intel drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops ttm ehci_pci drm aesni_intel aes_x86_64 glue_helper lrw gf128mul ablk_helper cryptd i2c_core > [ 2088.875474] sr_mod mptspi mptscsih ehci_hcd mptbase scsi_transport_spi e1000 uhci_hcd cdrom sunrpc dm_mirror dm_region_hash dm_log dm_mod autofs4 > [ 2088.876737] CPU: 1 PID: 6420 Comm: ping Not tainted 4.4.1-2980094.AroraKernelnextfruggeri.2.fc18.x86_64 #1 > [ 2088.878039] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 07/02/2012 > [ 2088.879521] task: ffff880035ea0000 ti: ffff8800b0ff8000 task.ti: ffff8800b0ff8000 > [ 2088.880285] RIP: 0010:[] [] skb_panic+0x66/0x68 > [ 2088.881214] RSP: 0018:ffff8800b0ffb728 EFLAGS: 00010292 > [ 2088.881945] RAX: 0000000000000083 RBX: ffff8800b51b6c00 RCX: 0000000000000000 > [ 2088.882692] RDX: ffff88013ae2f101 RSI: ffff88013ae2cae8 RDI: ffff88013ae2cae8 > [ 2088.883424] RBP: ffff8800b0ffb748 R08: 0000000000000000 R09: 00000000ffffffff > [ 2088.884110] R10: 00000000ffffffff R11: ffff88013621f3e0 R12: 0000000000000054 > [ 2088.884846] R13: ffffffff81a9fe40 R14: 0000000000000000 R15: 0000000003030303 > [ 2088.885535] FS: 00007f24b4a24740(0000) GS:ffff88013ae20000(0000) knlGS:0000000000000000 > [ 2088.886270] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > [ 2088.887014] CR2: 00007f9d6fb26000 CR3: 00000000aae66000 CR4: 00000000001406e0 > [ 2088.887817] Stack: > [ 2088.888582] ffff8800a5f6c3f8 0000000000000064 00000000000000c0 ffff880138fac000 > [ 2088.889378] ffff8800b0ffb758 ffffffff8143b640 ffff8800b0ffb7c8 ffffffff814c03f2 > [ 2088.890188] ffff880000000040 ffffffff00000040 ffff880000000000 000000000000002f > [ 2088.891011] Call Trace: > [ 2088.892073] [] skb_push+0x3b/0x3c > [ 2088.893156] [] iptunnel_xmit+0xad/0x145 > [ 2088.894033] [] ip_tunnel_xmit+0x673/0x790 [ip_tunnel] > [ 2088.894884] [] __gre_xmit+0x76/0x7f [ip_gre] > [ 2088.895700] [] ipgre_xmit+0xd3/0xef [ip_gre] > [ 2088.896573] [] dev_hard_start_xmit+0x226/0x2fc > [ 2088.897387] [] __dev_queue_xmit+0x333/0x425 > [ 2088.898183] [] dev_queue_xmit+0x10/0x12 > [ 2088.898996] [] neigh_direct_output+0x11/0x13 > [ 2088.899793] [] ip_finish_output2+0x233/0x293 > [ 2088.900582] [] ? dst_mtu+0xb/0xd > [ 2088.901283] [] ip_finish_output+0x146/0x159 > [ 2088.901990] [] ? ip_generic_getfrag+0x5c/0x98 > [ 2088.902658] [] ip_output+0x5f/0x91 > [ 2088.903306] [] ? ip_finish_output2+0x293/0x293 > [ 2088.903964] [] ? __ip_local_out+0x73/0x7c > [ 2088.904625] [] ? dst_mtu+0xd/0xd > [ 2088.905222] [] dst_output+0xf/0x11 > [ 2088.905820] [] ip_local_out+0x31/0x3a > [ 2088.906378] [] ip_send_skb+0x1a/0x3f > [ 2088.906938] [] ip_push_pending_frames+0x33/0x3b > [ 2088.907465] [] raw_sendmsg+0x794/0x8ea > [ 2088.907981] [] ? __skb_recv_datagram+0x201/0x487 > [ 2088.908548] [] ? skb_recv_datagram+0x32/0x34 > [ 2088.909050] [] ? raw_recvmsg+0x68/0x159 > [ 2088.909705] [] ? rw_copy_check_uvector+0x6e/0x109 > [ 2088.910247] [] inet_sendmsg+0x3c/0x65 > [ 2088.910775] [] sock_sendmsg_nosec+0x12/0x1d > [ 2088.911279] [] sock_sendmsg+0x29/0x2e > [ 2088.911764] [] ___sys_sendmsg+0x1a6/0x23f > [ 2088.912349] [] ? ldsem_up_read+0x1b/0x30 > [ 2088.912820] [] ? tty_ldisc_deref+0x16/0x18 > [ 2088.913299] [] ? tty_write+0x207/0x222 > [ 2088.913743] [] ? n_tty_receive_buf+0x13/0x13 > [ 2088.914244] [] ? __fget_light+0x2c/0x4d > [ 2088.914671] [] __sys_sendmsg+0x42/0x60 > [ 2088.915126] [] SyS_sendmsg+0x12/0x1e > [ 2088.915534] [] entry_SYSCALL_64_fastpath+0x12/0x71 > [ 2088.915947] Code: 00 00 48 89 44 24 10 8b 87 c8 00 00 00 48 89 44 24 08 48 8b 87 d8 00 00 00 48 c7 c7 29 ba 85 81 48 89 04 24 31 c0 e8 d4 4e bd ff <0f> 0b 0f 1f 44 00 00 55 48 89 e5 41 54 4c 8d a7 a8 01 00 00 53 > [ 2088.917397] RIP [] skb_panic+0x66/0x68 > [ 2088.917914] RSP > > I use this script, which creates gre tunnels t1 and t3, creates a tx > loop between them, then sends a packet through t3 and t1 before > dropping it with an iptables rule. > > ip link add dummy1 type dummy > ip addr add 1.1.1.1/32 dev dummy1 > ip link set dummy1 up > > ip link add dummy3 type dummy > ip addr add 3.3.3.3/32 dev dummy3 > ip link set dummy3 up > > ip tunnel add t1 mode gre local 1.1.1.1 remote 2.2.2.2 > ip link set t1 up > > ip tunnel add t3 mode gre local 3.3.3.3 remote 4.4.4.4 > ip link set t3 up > > ip route add 2.2.2.2 dev t3 > ip route add 4.4.4.4 dev t1 > > iptables -I OUTPUT -p gre -d 2.2.2.2 -j DROP > > ping -f 2.2.2.2 > > The root cause of the crash is that with every packet > t3->needed_headroom and t1->needed_headroom are strictly incremented > in ip_tunnel_xmit, since each one uses the other's needed_headroom. > > The immediate cause of the crash is that when needed_headroom wraps > around (in my case I get max_headroom = 65540 and t3->needed_headroom > = 4, max_headroom is unsigned int and needed_headroom is unsigned > short) skb_cow_head does not allocate enough headroom in the skb. > > I have not been able to come with a solution except not updating a > tunnel's needed_headroom, but that would have a performance impact > (see also http://marc.info/?l=linux-netdev&m=145594279014551&w=2). > Any suggestions? > > Thanks, > Francesco Ruggeri > I am not sure we want to support ~64K of headers. Is this something real, or just another root-exploit linux-bug-of-the-day trick ? When I want to reboot my host I usually type 'reboot', as it looks nicer to me ;)