BUG: Kernel NULL pointer dereference on write at 0x00000000 (rtmsg_ifinfo_build_skb)

[Paul Menzel <pmenzel@molgen.mpg.de>]

Dear Linux folks,


I do not know, if this is an rcutorture issue, or if rcutorture found a 
bug with `rtmsg_ifinfo_build_skb()`.


Building Linux 5.17-rc1+ (dd81e1c7d5fb) under Ubuntu 21.04 with

     CONFIG_TORTURE_TEST=y
     CONFIG_RCU_TORTURE_TEST=y

and

     $ clang --version
     Ubuntu clang version 12.0.0-3ubuntu1~21.04.2
     Target: powerpc64le-unknown-linux-gnu
     Thread model: posix
     InstalledDir: /usr/bin
     $ make -j100 LLVM=1 LLVM_IAS=0 bindeb-pkg

and booting it on an IBM S822LC, Linux paniced with a null pointer 
dereference, and the watchdog rebooted, and I found the message below in 
`/sys/fs/pstore/dmesg-nvram-2.enc.z`.

```
[    T1] Key type id_legacy registered
[    T1] SGI XFS with ACLs, security attributes, no debug enabled
[    T1] Block layer SCSI generic (bsg) driver version 0.4 loaded (major 
248)
[    T1] io scheduler mq-deadline registered
[    T1] io scheduler kyber registered
[  T198] cryptomgr_test (198) used greatest stack depth: 13536 bytes left
[    T1] pci 0021:10:00.0: enabling device (0141 -> 0143)
[    T1] Using unsupported 1024x768 (null) at 3fe882010000, depth=32, 
pitch=4096
[    T1] Console: switching to colour frame buffer device 128x48
[    T1] fb0: Open Firmware frame buffer device on 
/pciex@3fffe41100000/pci@0/pci@0/pci@b/pci@0/vga@0
[    T1] hvc0: raw protocol on /ibm,opal/consoles/serial@0 (boot console)
[    T1] hvc0: No interrupts property, using OPAL event
[    T1] Serial: 8250/16550 driver, 4 ports, IRQ sharing disabled
[    T1] Non-volatile memory driver v1.3
[    T1] brd: module loaded
[    T1] loop: module loaded
[    T1] ipr: IBM Power RAID SCSI Device Driver version: 2.6.4 (March 
14, 2017)
[    T1] ahci 0021:0e:00.0: version 3.0
[    T1] ahci 0021:0e:00.0: enabling device (0141 -> 0143)
[    T1] ahci 0021:0e:00.0: AHCI 0001.0000 32 slots 4 ports 6 Gbps 0xf 
impl SATA mode
[    T1] ahci 0021:0e:00.0: flags: 64bit ncq sntf led only pmp fbs pio 
slum part sxs
[    T1] scsi host0: ahci
[    T1] scsi host1: ahci
[    T1] scsi host2: ahci
[    T1] scsi host3: ahci
[    T1] ata1: SATA max UDMA/133 abar m2048@0x3fe881000000 port 
0x3fe881000100 irq 39
[    T1] ata2: SATA max UDMA/133 abar m2048@0x3fe881000000 port 
0x3fe881000180 irq 39
[    T1] ata3: SATA max UDMA/133 abar m2048@0x3fe881000000 port 
0x3fe881000200 irq 39
[    T1] ata4: SATA max UDMA/133 abar m2048@0x3fe881000000 port 
0x3fe881000280 irq 39
[    T1] e100: Intel(R) PRO/100 Network Driver
[    T1] e100: Copyright(c) 1999-2006 Intel Corporation
[    T1] e1000: Intel(R) PRO/1000 Network Driver
[    T1] e1000: Copyright (c) 1999-2006 Intel Corporation.
[    T1] e1000e: Intel(R) PRO/1000 Network Driver
[    T1] e1000e: Copyright(c) 1999 - 2015 Intel Corporation.
[    T1] ehci_hcd: USB 2.0 'Enhanced' Host Controller (EHCI) Driver
[    T1] ehci-pci: EHCI PCI platform driver
[    T1] ohci_hcd: USB 1.1 'Open' Host Controller (OHCI) Driver
[    T1] ohci-pci: OHCI PCI platform driver
[    T1] rtc-opal opal-rtc: registered as rtc0
[    T1] rtc-opal opal-rtc: setting system clock to 2022-01-24T18:21:45 
UTC (1643048505)
[    T1] i2c_dev: i2c /dev entries driver
[    T1] device-mapper: uevent: version 1.0.3
[    T1] device-mapper: ioctl: 4.45.0-ioctl (2021-03-22) initialised: 
dm-devel@redhat.com
[    T1] powernv-cpufreq: cpufreq pstate min 0xffffffd5 nominal 
0xffffffef max 0x0
[    T1] powernv-cpufreq: Workload Optimized Frequency is disabled in 
the platform
[    T1] powernv_idle_driver registered
[    T1] nx_compress_powernv: coprocessor found on chip 0, CT 3 CI 1
[    T1] nx_compress_powernv: coprocessor found on chip 8, CT 3 CI 9
[    T1] usbcore: registered new interface driver usbhid
[    T1] usbhid: USB HID core driver
[    T1] ipip: IPv4 and MPLS over IPv4 tunneling driver
[    T1] NET: Registered PF_INET6 protocol family
[    T1] Segment Routing with IPv6
[    T1] In-situ OAM (IOAM) with IPv6
[    T1] sit: IPv6, IPv4 and MPLS over IPv4 tunneling driver
[    T1] BUG: Kernel NULL pointer dereference on write at 0x00000000
[    T1] Faulting instruction address: 0xc0000000008e2400
[    T1] Oops: Kernel access of bad area, sig: 11 [#1]
[    T1] LE PAGE_SIZE=64K MMU=Hash PREEMPT SMP NR_CPUS=16 NUMA PowerNV
[    T1] Modules linked in:
[    T1] CPU: 11 PID: 1 Comm: swapper/0 Not tainted 
5.17.0-rc1-00032-gdd81e1c7d5fb #29
[    T1] NIP:  c0000000008e2400 LR: c000000000d65db0 CTR: c000000000f0bb60
[    T1] REGS: c0000000125033e0 TRAP: 0380   Not tainted 
(5.17.0-rc1-00032-gdd81e1c7d5fb)
[    T1] MSR:  9000000000009033 <SF,HV,EE,ME,IR,DR,RI,LE>  CR: 42800c40 
XER: 00000000
[    T1] CFAR: c000000000d65dac IRQMASK: 0
[    T1] GPR00: c000000000d65b40 c000000012503680 c00000000290c600 
0000000000000000
[    T1] GPR04: ffffffffffffffff 00000000ffffffff 0000000000000000 
0000000000000cc0
[    T1] GPR08: 0000000000000000 0000000000000000 ffffffffffffffff 
0000000000000001
[    T1] GPR12: 0000000000000000 c000007fffff6c00 c000000000012478 
0000000000000000
[    T1] GPR16: 0000000000000000 0000000000000000 0000000000000000 
0000000000000000
[    T1] GPR20: 0000000000000000 c000000002810100 0000000000000cc0 
0000000000000000
[    T1] GPR24: 0000000000000010 c00000000294cf50 0000000000000000 
0000000000000000
[    T1] GPR28: 0000000000000000 c00000001ec61000 0000000000000000 
c000000012503680
[    T1] NIP [c0000000008e2400] strlen+0x10/0x30
[    T1] LR [c000000000d65db0] if_nlmsg_size+0x150/0x360
[    T1] Call Trace:
[    T1] [c000000012503680] [c0000000125036c0] 0xc0000000125036c0 
(unreliable)
[    T1] [c0000000125036f0] [c000000000d65b40] 
rtmsg_ifinfo_build_skb+0x80/0x1a0
[    T1] [c0000000125037b0] [c000000000d66be0] rtmsg_ifinfo+0x70/0xd0
[    T1] [c000000012503800] [c000000000d4de50] 
register_netdevice+0x690/0x770
[    T1] [c000000012503890] [c000000000d4e2bc] register_netdev+0x4c/0x80
[    T1] [c0000000125038c0] [c000000000f4784c] sit_init_net+0x10c/0x1d0
[    T1] [c000000012503910] [c000000000d33c0c] ops_init+0x13c/0x1b0
[    T1] [c000000012503970] [c000000000d331bc] 
register_pernet_operations+0xec/0x1e0
[    T1] [c0000000125039d0] [c000000000d33440] 
register_pernet_device+0x60/0xd0
[    T1] [c000000012503a20] [c000000002085478] sit_init+0x54/0x160
[    T1] [c000000012503ab0] [c000000000011ba8] do_one_initcall+0xd8/0x3b0
[    T1] [c000000012503c70] [c000000002006064] do_initcall_level+0xe4/0x1c4
[    T1] [c000000012503cc0] [c000000002005f20] do_initcalls+0x84/0xe4
[    T1] [c000000012503d40] [c000000002005c7c] 
kernel_init_freeable+0x160/0x1ec
[    T1] [c000000012503da0] [c0000000000124ac] kernel_init+0x3c/0x270
[    T1] [c000000012503e10] [c00000000000cd64] 
ret_from_kernel_thread+0x5c/0x64
[    T1] Instruction dump:
[    T1] eb81ffe0 7c0803a6 4e800020 00000000 00000000 00000000 60000000 
60000000
[    T1] 3883ffff 60000000 60000000 60000000 <8ca40001> 28050000 
4082fff8 7c632050
[    T1] ---[ end trace 0000000000000000 ]---
[    T1]
[  T206] ata4: SATA link down (SStatus 0 SControl 300)
[  T204] ata3: SATA link down (SStatus 0 SControl 300)
[  T200] ata1: SATA link up 6.0 Gbps (SStatus 133 SControl 300)
[  T200] ata1.00: ATA-10: ST1000NX0313         00LY266 00LY265IBM, BE33, 
max UDMA/133
[  T200] ata1.00: 1953525168 sectors, multi 0: LBA48 NCQ (depth 32), AA
[  T200] ata1.00: configured for UDMA/133
[    T7] scsi 0:0:0:0: Direct-Access     ATA      ST1000NX0313     BE33 
PQ: 0 ANSI: 5
[    T7] sd 0:0:0:0: Attached scsi generic sg0 type 0
[  T209] sd 0:0:0:0: [sda] 1953525168 512-byte logical blocks: (1.00 
TB/932 GiB)
[  T209] sd 0:0:0:0: [sda] 4096-byte physical blocks
[  T209] sd 0:0:0:0: [sda] Write Protect is off
[  T209] sd 0:0:0:0: [sda] Mode Sense: 00 3a 00 00
[  T209] sd 0:0:0:0: [sda] Write cache: enabled, read cache: enabled, 
doesn't support DPO or FUA
[  T209]  sda: sda1 sda2
[  T209] sd 0:0:0:0: [sda] Attached SCSI removable disk
[    T1] Kernel panic - not syncing: Attempted to kill init! 
exitcode=0x0000000b
```


Kind regards,

Paul