[lxc-users] kernel crash when starting an unprivileged container

[Tomasz Chmielewski]

I'm trying to start an unprivileged container on Ubuntu 14.04; 
unfortunately, the kernel crashes.


# lxc-create -t download -n test-container
(...)
Distribution: ubuntu
Release: trusty
Architecture: amd64
(...)

# lxc-start -n test-container -F

Kernel crashes at this point.

It does not crash if I start the container as privileged.


- kernel used is 4.0.4-040004-generic from 
http://kernel.ubuntu.com/~kernel-ppa/mainline/v4.0.4-wily/

- lxc userspace: http://ppa.launchpad.net/ubuntu-lxc/stable/ubuntu

# dpkg -l|grep lxc
ii  liblxc1                                  
1.1.2-0ubuntu3~ubuntu14.04.1~ppa1    amd64        Linux Containers 
userspace tools (library)
ii  lxc                                      
1.1.2-0ubuntu3~ubuntu14.04.1~ppa1    amd64        Linux Containers 
userspace tools
ii  lxc-templates                            
1.1.2-0ubuntu3~ubuntu14.04.1~ppa1    amd64        Linux Containers 
userspace tools (templates)
ii  lxcfs                                    
0.7-0ubuntu4~ubuntu14.04.1~ppa1      amd64        FUSE based filesystem 
for LXC
ii  python3-lxc                              
1.1.2-0ubuntu3~ubuntu14.04.1~ppa1    amd64        Linux Containers 
userspace tools (Python 3.x bindings)



It's a bit hard to get the printout of the OOPS, as I'm only able to 
access the server remotely and it doesn't manage to write the OOPS to 
the log.

Anyway, after a few crashes and "while true; do dmesg -c ; done" I was 
able to capture this:

[  237.706914] device vethPI4H7F entered promiscuous mode
[  237.707006] IPv6: ADDRCONF(NETDEV_UP): vethPI4H7F: link is not ready
[  237.797284] eth0: renamed from veth1OSOTS
[  237.824526] IPv6: ADDRCONF(NETDEV_CHANGE): vethPI4H7F: link becomes 
ready
[  237.824556] lxcbr0: port 1(vethPI4H7F) entered forwarding state
[  237.824562] lxcbr0: port 1(vethPI4H7F) entered forwarding state
[  237.928179] BUG: unable to handle kernel NULL pointer dereference at  
          (null)
[  237.928262] IP: [<ffffffff8122f888>] pin_remove+0x58/0xf0
[  237.928318] PGD 0
[  237.928364] Oops: 0002 [#1] SMP
[  237.928432] Modules linked in: xt_conntrack veth xt_CHECKSUM 
iptable_mangle ipt_MASQUERADE nf_nat_masquerade_ipv4 iptable_nat 
nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 nf_nat nf_conntrack 
xt_tcpudp iptable_filter ip_tables x_tables bridge stp llc intel_rapl 
iosf_mbi x86_pkg_temp_thermal intel_powerclamp coretemp kvm_intel kvm 
crct10dif_pclmul crc32_pclmul eeepc_wmi ghash_clmulni_intel aesni_intel 
asus_wmi sparse_keymap ie31200_edac aes_x86_64 edac_core lrw gf128mul 
glue_helper shpchp lpc_ich ablk_helper cryptd mac_hid 8250_fintek 
serio_raw tpm_infineon video wmi btrfs lp parport raid10 raid456 
async_raid6_recov async_memcpy async_pq async_xor async_tx xor raid6_pq 
e1000e raid1 ahci raid0 ptp libahci pps_core multipath linear
[  237.930151] CPU: 2 PID: 6568 Comm: lxc-start Not tainted 
4.0.4-040004-generic #201505171336
[  237.930188] Hardware name: System manufacturer System Product 
Name/P8B WS, BIOS 0904 10/24/2011
[  237.930225] task: ffff880806970a00 ti: ffff8808090c8000 task.ti: 
ffff8808090c8000
[  237.930259] RIP: 0010:[<ffffffff8122f888>]  [<ffffffff8122f888>] 
pin_remove+0x58/0xf0
[  237.930341] RSP: 0018:ffff8808090cbe18  EFLAGS: 00010246
[  237.930383] RAX: 0000000000000000 RBX: ffff880808808a20 RCX: 
dead000000100100
[  237.930429] RDX: 0000000000000000 RSI: dead000000200200 RDI: 
ffffffff81f9a548
[  237.930474] RBP: ffff8808090cbe28 R08: ffffffff81d11b60 R09: 
0000000000000100
[  237.930572] R13: ffff880806970a00 R14: ffffffff81ecd070 R15: 
00007ffe57fd5540
[  237.930618] FS:  00007fd4aaaa48c0(0000) GS:ffff88082fa80000(0000) 
knlGS:0000000000000000
[  237.930685] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  237.930728] CR2: 0000000000000000 CR3: 00000008099c1000 CR4: 
00000000000407e0
[  237.930773] Stack:
[  237.930809]  ffff880806970a00 ffff880808808a20 ffff8808090cbe48 
ffffffff8121d0f2
[  237.930957]  ffff8808090cbe68 ffff880808808a20 ffff8808090cbea8 
ffffffff8122fa55
[  237.931123]  0000000000000000 ffff880806970a00 ffffffff810bb2b0 
ffff8808090cbe70
[  237.931286] Call Trace:
[  237.931336]  [<ffffffff8121d0f2>] drop_mountpoint+0x22/0x40
[  237.931380]  [<ffffffff8122fa55>] pin_kill+0x75/0x130
[  237.931425]  [<ffffffff810bb2b0>] ? prepare_to_wait_event+0x100/0x100
[  237.931471]  [<ffffffff8122fb39>] mnt_pin_kill+0x29/0x40
[  237.931530]  [<ffffffff8121baf0>] cleanup_mnt+0x80/0x90
[  237.931573]  [<ffffffff8121bb52>] __cleanup_mnt+0x12/0x20
[  237.931617]  [<ffffffff81096ad7>] task_work_run+0xb7/0xf0
[  237.931662]  [<ffffffff8101607c>] do_notify_resume+0xbc/0xd0
[  237.931709]  [<ffffffff817f0beb>] int_signal+0x12/0x17



-- 
Tomasz Chmielewski
http://wpkg.org