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:[<ffffffff81522130>] [<ffffffff81522130>] > 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] [<ffffffff8143b640>] skb_push+0x3b/0x3c > [ 2088.893156] [<ffffffff814c03f2>] iptunnel_xmit+0xad/0x145 > [ 2088.894033] [<ffffffffa0563ee3>] ip_tunnel_xmit+0x673/0x790 [ip_tunnel] > [ 2088.894884] [<ffffffffa0568645>] __gre_xmit+0x76/0x7f [ip_gre] > [ 2088.895700] [<ffffffffa05691fa>] ipgre_xmit+0xd3/0xef [ip_gre] > [ 2088.896573] [<ffffffff8144c9e7>] dev_hard_start_xmit+0x226/0x2fc > [ 2088.897387] [<ffffffff8144cf0c>] __dev_queue_xmit+0x333/0x425 > [ 2088.898183] [<ffffffff8144d01e>] dev_queue_xmit+0x10/0x12 > [ 2088.898996] [<ffffffff81453120>] neigh_direct_output+0x11/0x13 > [ 2088.899793] [<ffffffff814876a3>] ip_finish_output2+0x233/0x293 > [ 2088.900582] [<ffffffff81486894>] ? dst_mtu+0xb/0xd > [ 2088.901283] [<ffffffff81487849>] ip_finish_output+0x146/0x159 > [ 2088.901990] [<ffffffff81486b02>] ? ip_generic_getfrag+0x5c/0x98 > [ 2088.902658] [<ffffffff81488874>] ip_output+0x5f/0x91 > [ 2088.903306] [<ffffffff81487703>] ? ip_finish_output2+0x293/0x293 > [ 2088.903964] [<ffffffff81488220>] ? __ip_local_out+0x73/0x7c > [ 2088.904625] [<ffffffff81486896>] ? dst_mtu+0xd/0xd > [ 2088.905222] [<ffffffff814868a5>] dst_output+0xf/0x11 > [ 2088.905820] [<ffffffff8148825a>] ip_local_out+0x31/0x3a > [ 2088.906378] [<ffffffff81489117>] ip_send_skb+0x1a/0x3f > [ 2088.906938] [<ffffffff8148916f>] ip_push_pending_frames+0x33/0x3b > [ 2088.907465] [<ffffffff814a7c71>] raw_sendmsg+0x794/0x8ea > [ 2088.907981] [<ffffffff8144119c>] ? __skb_recv_datagram+0x201/0x487 > [ 2088.908548] [<ffffffff81441454>] ? skb_recv_datagram+0x32/0x34 > [ 2088.909050] [<ffffffff814a7267>] ? raw_recvmsg+0x68/0x159 > [ 2088.909705] [<ffffffff8113ed4e>] ? rw_copy_check_uvector+0x6e/0x109 > [ 2088.910247] [<ffffffff814b40ba>] inet_sendmsg+0x3c/0x65 > [ 2088.910775] [<ffffffff81434c88>] sock_sendmsg_nosec+0x12/0x1d > [ 2088.911279] [<ffffffff81434cbc>] sock_sendmsg+0x29/0x2e > [ 2088.911764] [<ffffffff81435f2f>] ___sys_sendmsg+0x1a6/0x23f > [ 2088.912349] [<ffffffff81331e0a>] ? ldsem_up_read+0x1b/0x30 > [ 2088.912820] [<ffffffff81330143>] ? tty_ldisc_deref+0x16/0x18 > [ 2088.913299] [<ffffffff81329cf8>] ? tty_write+0x207/0x222 > [ 2088.913743] [<ffffffff8132e102>] ? n_tty_receive_buf+0x13/0x13 > [ 2088.914244] [<ffffffff81154673>] ? __fget_light+0x2c/0x4d > [ 2088.914671] [<ffffffff814363f2>] __sys_sendmsg+0x42/0x60 > [ 2088.915126] [<ffffffff81436422>] SyS_sendmsg+0x12/0x1e > [ 2088.915534] [<ffffffff815274ae>] 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 [<ffffffff81522130>] skb_panic+0x66/0x68 > [ 2088.917914] RSP <ffff8800b0ffb728> > > 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 ;)
