linux-kernel - Re: PROBLEM: NULL pointer dereference in kernel 4.14.6

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Message-ID: <08995310-d853-ee77-ed1f-26cc336a4a30@incorrekt.com>
Date:   Sun, 17 Dec 2017 17:49:44 +0000
From:   Bronek Kozicki <brok@...orrekt.com>
To:     Bronek Kozicki <brok@...orrekt.com>, linux-kernel@...r.kernel.org
Subject: Re: PROBLEM: NULL pointer dereference in kernel 4.14.6

I just upgraded to 4.14.7 and tried to reproduce this error, this time under strace. As you can see this happens when systemctl tries to read a specific entry under /sys/fs . In case this matters, the entry is for a small virtual machine running under qemu/kvm and managed by libvirt.

open("/sys/fs/cgroup/unified/machine.slice", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 5
fstat(5, {st_mode=S_IFDIR|0755, st_size=0, ...}) = 0
getdents(5, /* 12 entries */, 32768)    = 464
openat(AT_FDCWD, "/sys/fs/cgroup/unified/machine.slice/machine-qemu\\x2d1\\x2dkartuzy\\x2dspice.scope/cgroup.procs", O_RDONLY|O_CLOEXEC) = 8
fstat(8, {st_mode=S_IFREG|0644, st_size=0, ...}) = 0
read(8,  <unfinished ...>)              = ?
+++ killed by SIGKILL +++
[1]    12078 killed     strace -- systemctl status


B.


[ 1889.226051] ================================================================================
[ 1889.235286] UBSAN: Undefined behaviour in kernel/cgroup/pids.c:67:9
[ 1889.241563] member access within null pointer of type 'struct pids_cgroup'
[ 1889.249920] ================================================================================
[ 1889.259698] BUG: unable to handle kernel NULL pointer dereference at 00000000000000b0
[ 1889.267524] IP: pids_free+0x28/0xb0
[ 1889.272394] PGD 0 P4D 0
[ 1889.274925] Oops: 0000 [#1] SMP
[ 1889.278061] Modules linked in: ebtable_filter ebtables ip6table_filter ip6_tables iptable_filter devlink joydev hid_logitech_hidpp mxm_wmi intel_rapl sb_edac x86_pkg_temp_thermal intel_powerclamp coretemp kvm_intel kvm crct10dif_pclmul crc32_pclmu
l crc32c_intel ghash_clmulni_intel pcbc aesni_intel aes_x86_64 crypto_simd glue_helper cryptd ext4 intel_cstate crc16 mbcache jbd2 fscrypto nls_iso8859_1 nls_cp437 evdev input_leds led_class vfat fat intel_rapl_perf mac_hid pcspkr hid_logitech_dj igb ptp mei_me pps_
core i2c_i801 i2c_algo_bit mei lpc_ich ioatdma tpm_tis tpm_tis_core dca shpchp tpm wmi button sch_fq_codel sg ip_tables x_tables usbhid hid zfs(PO) zunicode(PO) zavl(PO) icp(PO) sd_mod serio_raw atkbd libps2 isci ahci libsas libahci xhci_pci ehci_pci mpt3sas xhci_hc
d ehci_hcd raid_class libata
[ 1889.349864]  scsi_transport_sas usbcore scsi_mod usb_common i8042 serio zcommon(PO) znvpair(PO) spl(O) nvme nvme_core bridge stp llc vhost_net tun tap vhost vfio_pci irqbypass vfio_virqfd vfio_iommu_type1 vfio
[ 1889.368439] CPU: 1 PID: 12084 Comm: systemctl Tainted: P        W  O    4.14.7-1-ARCH #1
[ 1889.376525] Hardware name: Supermicro X9DA7/E/X9DA7/E, BIOS 3.0a 07/02/2014
[ 1889.383474] task: ffff93149aaec140 task.stack: ffffa88c3836c000
[ 1889.389387] RIP: 0010:pids_free+0x28/0xb0
[ 1889.393388] RSP: 0018:ffffa88c3836fcc8 EFLAGS: 00010282
[ 1889.398605] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000006
[ 1889.405731] RDX: 0000000000000000 RSI: 0000000000000202 RDI: 0000000000000202
[ 1889.412854] RBP: ffff931499ab2d58 R08: 000000000000079a R09: 0000000000000000
[ 1889.419979] R10: 00000000001f5954 R11: 000000000003d040 R12: 0000000056e21a48
[ 1889.427102] R13: ffffffffa91de5c0 R14: ffff93247b0598c0 R15: ffffffffa91cd0a0
[ 1889.434227] FS:  00007f18eee6b8c0(0000) GS:ffff931ebfa40000(0000) knlGS:0000000000000000
[ 1889.442302] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1889.448041] CR2: 00000000000000b0 CR3: 0000000611019003 CR4: 00000000001626e0
[ 1889.455164] Call Trace:
[ 1889.457610]  cgroup_free+0xaa/0x190
[ 1889.461095]  __put_task_struct+0x68/0x230
[ 1889.465105]  ? seq_printf+0x4e/0x70
[ 1889.468591]  css_task_iter_next+0x74/0x90
[ 1889.472594]  kernfs_seq_next+0x58/0x110
[ 1889.476424]  seq_read+0x36c/0x620
[ 1889.479735]  __vfs_read+0x54/0x2e0
[ 1889.483134]  vfs_read+0x9d/0x200
[ 1889.486358]  SyS_read+0x52/0xc0
[ 1889.489494]  do_syscall_64+0x69/0x1e0
[ 1889.493152]  entry_SYSCALL64_slow_path+0x25/0x25
[ 1889.497771] RIP: 0033:0x7f18ee784a11
[ 1889.501341] RSP: 002b:00007ffd56942618 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
[ 1889.508897] RAX: ffffffffffffffda RBX: 0000559a9ae6d260 RCX: 00007f18ee784a11
[ 1889.516022] RDX: 0000000000001000 RSI: 0000559a9ae80f70 RDI: 0000000000000008
[ 1889.523145] RBP: 0000000000000d68 R08: 0000000000000003 R09: ffffffffffffffb0
[ 1889.530270] R10: 0000000000001000 R11: 0000000000000246 R12: 00007f18eea4b700
[ 1889.537395] R13: 00007f18eea4c240 R14: 0000559a9ae6d260 R15: 0000000000000000
[ 1889.544518] Code: 44 00 00 0f 1f 44 00 00 48 81 ff c8 f7 ff ff 55 53 48 89 fb 74 4c 48 8b 9b 38 08 00 00 48 85 db 74 7c 48 8b 5b 50 48 85 db 74 63 <48> 83 bb b0 00 00 00 00 74 2a 48 c7 c5 60 2e 1e a9 48 89 df e8
[ 1889.563368] RIP: pids_free+0x28/0xb0 RSP: ffffa88c3836fcc8
[ 1889.568846] CR2: 00000000000000b0
[ 1889.572175] ---[ end trace eab2ed000b4d5c66 ]---