Crash in cgroup_procs_show

[Laura Abbott]

Hi,

Fedora got a bug report on 4.14.4 of a crash on
reboot https://bugzilla.redhat.com/show_bug.cgi?id=1525279

 BUG: unable to handle kernel NULL pointer dereference at 0000000000000254
 IP: __task_pid_nr_ns+0xc7/0xf0
 PGD 0 P4D 0
 Oops: 0000 [#1] SMP
 Modules linked in: fuse vhost_net vhost tap xt_CHECKSUM ipt_MASQUERADE nf_nat_masquerade_ipv4 tun nf_conntrack_netbios_ns nf_conntrack_broadcast xt_CT xt_nat xt_mark ip6t_rpfilter ip6t_REJECT nf_reject_ipv6 xt_conntrack ip_set nfnetlink ebtable_nat ebtable_broute ip6table_nat nf_conntrack_ipv6 nf_defrag_ipv6 nf_nat_ipv6 ip6table_mangle ip6table_raw ip6table_security iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 nf_nat nf_conntrack libcrc32c iptable_mangle bridge iptable_raw stp llc iptable_security ebtable_filter ebtables ip6table_filter ip6_tables sunrpc vfat fat edac_mce_amd eeepc_wmi kvm_amd asus_wmi wmi_bmof sparse_keymap rfkill video kvm snd_hda_codec_realtek snd_hda_codec_generic snd_hda_codec_hdmi irqbypass crct10dif_pclmul snd_hda_intel crc32_pclmul snd_hda_codec ghash_clmulni_intel
  snd_hda_core snd_hwdep snd_seq joydev snd_seq_device snd_pcm snd_timer sp5100_tco i2c_piix4 ccp snd soundcore tpm_tis shpchp tpm_tis_core tpm wmi acpi_cpufreq binfmt_misc btrfs xor zstd_decompress zstd_compress xxhash raid6_pq hid_logitech_hidpp amdkfd amd_iommu_v2 amdgpu i2c_algo_bit drm_kms_helper ttm drm crc32c_intel r8169 hid_logitech_dj mii nvme nvme_core i2c_dev
 CPU: 2 PID: 1 Comm: systemd Not tainted 4.14.4-200.fc26.x86_64 #1
 Hardware name: System manufacturer System Product Name/PRIME B350M-A, BIOS 3203 11/09/2017
 task: ffff88c4baee8000 task.stack: ffff96d5c3158000
 RIP: 0010:__task_pid_nr_ns+0xc7/0xf0
 RSP: 0018:ffff96d5c315bd50 EFLAGS: 00010206
 RAX: 0000000000000000 RBX: ffff88c4b68c6000 RCX: 0000000000000250
 RDX: ffffffffa5e47960 RSI: 0000000000000000 RDI: ffff88c490f6ab00
 RBP: ffff96d5c315bd50 R08: 0000000000001000 R09: 0000000000000005
 R10: ffff88c4be006b80 R11: ffff88c42f1b8004 R12: ffff96d5c315bf18
 R13: ffff88c42d7dd200 R14: ffff88c490f6a510 R15: ffff88c4b68c6000
 FS:  00007f9446f8ea00(0000) GS:ffff88c4be680000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 0000000000000254 CR3: 00000007f956f000 CR4: 00000000003406e0
 Call Trace:
  cgroup_procs_show+0x19/0x30
  cgroup_seqfile_show+0x4c/0xb0
  kernfs_seq_show+0x21/0x30
  seq_read+0x2ec/0x3f0
  kernfs_fop_read+0x134/0x180
  __vfs_read+0x37/0x160
  ? security_file_permission+0x9b/0xc0
  vfs_read+0x8e/0x130
  SyS_read+0x55/0xc0
  entry_SYSCALL_64_fastpath+0x1a/0xa5
 RIP: 0033:0x7f94455f942d
 RSP: 002b:00007ffe81ba2d00 EFLAGS: 00000293 ORIG_RAX: 0000000000000000
 RAX: ffffffffffffffda RBX: 00005574e2233f00 RCX: 00007f94455f942d
 RDX: 0000000000001000 RSI: 00005574e2321a90 RDI: 000000000000002b
 RBP: 0000000000000000 R08: 00005574e2321a90 R09: 00005574e231de60
 R10: 00007f94458c8b38 R11: 0000000000000293 R12: 00007f94458c8ae0
 R13: 00007ffe81ba3800 R14: 0000000000000000 R15: 00005574e2116560
 Code: 04 74 0e 89 f6 48 8d 04 76 48 8d 04 c5 f0 05 00 00 48 8b bf b8 05 00 00 48 01 c7 31 c0 48 8b 0f 48 85 c9 74 18 8b b2 30 08 00 00 <3b> 71 04 77 0d 48 c1 e6 05 48 01 f1 48 3b 51 38 74 09 5d c3 8b
 RIP: __task_pid_nr_ns+0xc7/0xf0 RSP: ffff96d5c315bd50

It looks like a few others reported similar problems

https://marc.info/?l=linux-kernel&m=151210295120013
https://marc.info/?l=linux-kernel&m=151151651301420

I haven't yet asked the reporter to try and bisect. Is there a fix queued
up for this yet?

Thanks,
Laura