Comment 0 for bug 1748671

Got this bug/oops while running with the linux-image-4.4.0-113-generic (4.4.0-113.136) kernel from -proposed:

BUG: unable to handle kernel NULL pointer dereference at 0000000000000009
IP: [<ffffffffab413ad5>] csum_and_copy_from_iter+0x55/0x4c0
PGD 0
Oops: 0000 [#1] SMP
Modules linked in: ctr ccm veth xt_CHECKSUM iptable_mangle xt_comment ec_sys bridge stp llc nf_log_ipv6 ip6table_filter ip6t_MASQUERADE nf_nat_masquerade_ipv6 ip6table_nat nf_nat_ipv6 ip6_tables nf_log_ip
 snd ghash_clmulni_intel soundcore r8169 psmouse input_leds cfg80211 rtsx_pci mii vhost_net vhost media ahci libahci macvtap macvlan mei_me mei kvm_intel kvm irqbypass tpm_crb i2c_hid intel_lpss_acpi inte
CPU: 2 PID: 3997 Comm: dnsmasq Tainted: P W O 4.4.0-113-generic #136-Ubuntu
Hardware name: System76 Lemur/Lemur, BIOS 5.12 02/17/2017
task: ffff880830269e00 ti: ffff880035c44000 task.ti: ffff880035c44000
RIP: 0010:[<ffffffffab413ad5>] [<ffffffffab413ad5>] csum_and_copy_from_iter+0x55/0x4c0
RSP: 0018:ffff880035c47a18 EFLAGS: 00010246
RAX: 00000000ab729fd0 RBX: 000000000000001c RCX: ffff880035c47e98
RDX: ffff880035c47a94 RSI: 000000000000001c RDI: ffff8807ef1a7424
RBP: ffff880035c47a80 R08: 0000000000000000 R09: ffff8807ef1a7424
R10: ffff8807ef1a7424 R11: ffff8807ef1a7400 R12: ffff880035c47e98
R13: 0000000000000000 R14: 00ffffffabea6920 R15: 0000000000000001
FS: 00007ff2b234d880(0000) GS:ffff88086ed00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000009 CR3: 0000000035c1e000 CR4: 0000000000360670
Stack:
 ffff88084e001600 ffffffffab72d1d7 ffff880830f18500 ffff880035c47aaf
 ffff880035c47a94 00000000000001c0 00000000ffffffff b0f4001fc4815eea
 000000000000001c ffff880830f18500 0000000000000000 ffff880035c47d30
Call Trace:
 [<ffffffffab72d1d7>] ? __alloc_skb+0x87/0x1f0
 [<ffffffffab782cb6>] ip_generic_getfrag+0x56/0xe0
 [<ffffffffab7abc0f>] raw_getfrag+0xaf/0x100
 [<ffffffffab78450a>] __ip_append_data.isra.45+0x98a/0xb90
 [<ffffffffab7abb60>] ? raw_recvmsg+0x1c0/0x1c0
 [<ffffffffab7abb60>] ? raw_recvmsg+0x1c0/0x1c0
 [<ffffffffab78478a>] ip_append_data.part.46+0x7a/0xe0
 [<ffffffffab785474>] ip_append_data+0x34/0x40
 [<ffffffffab7ac8a4>] raw_sendmsg+0x724/0xc00
 [<ffffffffab3a4ea0>] ? aa_sk_perm+0x70/0x210
 [<ffffffffab3a5761>] ? aa_sock_msg_perm+0x61/0x150
 [<ffffffffab7bc91b>] inet_sendmsg+0x6b/0xa0
 [<ffffffffab723b5e>] sock_sendmsg+0x3e/0x50
 [<ffffffffab724151>] SYSC_sendto+0x101/0x190
 [<ffffffffab729fd0>] ? sock_setsockopt+0x180/0x830
 [<ffffffffab397072>] ? apparmor_socket_setsockopt+0x22/0x30
 [<ffffffffab724c7e>] SyS_sendto+0xe/0x10
 [<ffffffffab84df9f>] entry_SYSCALL_64_fastpath+0x1c/0x93
Code: f3 48 0f 47 de 48 85 db 0f 84 8b 01 00 00 8b 02 49 89 f9 49 89 cc 4c 8b 71 08 89 45 c4 8b 01 a8 04 0f 85 79 01 00 00 4c 8b 79 18 <4d> 8b 6f 08 4d 29 f5 49 39 dd 4c 0f 47 eb a8 02 0f 85 36 02 00
RIP [<ffffffffab413ad5>] csum_and_copy_from_iter+0x55/0x4c0
 RSP <ffff880035c47a18>
CR2: 0000000000000009
---[ end trace bdd9157c94a456b6 ]---

The trigger is when I start an artful lxd container and it tries to get an IPv4/IPv6. Oddly enough, the same thing works perfectly for my xenial container. My lxd-bridge has dnsmasq contained by Apparmor which is non standard but always worked flawlessly.

I can trigger the bug 100% of the time so validating any tentative fix should be easy.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: linux-image-4.4.0-113-generic 4.4.0-113.136
ProcVersionSignature: Ubuntu 4.4.0-112.135-generic 4.4.98
Uname: Linux 4.4.0-112-generic x86_64
NonfreeKernelModules: zfs zunicode zcommon znvpair zavl
ApportVersion: 2.20.1-0ubuntu2.15
Architecture: amd64
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC0: simon 7244 F.... pulseaudio
CurrentDesktop: Unity
CurrentDmesg: Error: command ['dmesg'] failed with exit code 1: dmesg: read kernel buffer failed: Operation not permitted
Date: Sat Feb 10 16:45:26 2018
HibernationDevice: RESUME=/dev/mapper/nvme0n1p3_crypt
InstallationDate: Installed on 2016-12-06 (431 days ago)
InstallationMedia: Ubuntu-Server 16.04.1 LTS "Xenial Xerus" - Beta amd64 (20161206)
MachineType: System76 Lemur
ProcFB: 0 inteldrmfb
ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-4.4.0-112-generic.efi.signed root=UUID=49432620-38ed-44bd-912a-7bc51eec3a35 ro quiet splash possible_cpus=4 nmi_watchdog=0 kaslr vsyscall=none vt.handoff=7
RelatedPackageVersions:
 linux-restricted-modules-4.4.0-112-generic N/A
 linux-backports-modules-4.4.0-112-generic N/A
 linux-firmware 1.157.16
RfKill: Error: [Errno 2] No such file or directory: 'rfkill'
SourcePackage: linux
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 02/17/2017
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: 5.12
dmi.board.asset.tag: Tag 12345
dmi.board.name: Lemur
dmi.board.vendor: System76
dmi.board.version: lemu7
dmi.chassis.asset.tag: No Asset Tag
dmi.chassis.type: 10
dmi.chassis.vendor: System76
dmi.chassis.version: N/A
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvr5.12:bd02/17/2017:svnSystem76:pnLemur:pvrlemu7:rvnSystem76:rnLemur:rvrlemu7:cvnSystem76:ct10:cvrN/A:
dmi.product.name: Lemur
dmi.product.version: lemu7
dmi.sys.vendor: System76