Re: [seccomp] kernel BUG at kernel/fork.c:1102!
From: Kees Cook
Date: Thu Nov 06 2014 - 11:47:34 EST
I believe this has been fixed for a while by
69f6a34bdeea4fec50bb90619bc9602973119572 "seccomp: Replace
BUG(!spin_is_locked()) with assert_spin_lock"
Thanks!
-Kees
On Wed, Nov 5, 2014 at 11:14 PM, Fengguang Wu <fengguang.wu@xxxxxxxxx> wrote:
> Greetings,
>
> 0day kernel testing robot got the below dmesg and the first bad commit is
>
> commit dbd952127d11bb44a4ea30b08cc60531b6a23d71
> Author: Kees Cook <keescook@xxxxxxxxxxxx>
> AuthorDate: Fri Jun 27 15:18:48 2014 -0700
> Commit: Kees Cook <keescook@xxxxxxxxxxxx>
> CommitDate: Fri Jul 18 12:13:39 2014 -0700
>
> seccomp: introduce writer locking
>
> Normally, task_struct.seccomp.filter is only ever read or modified by
> the task that owns it (current). This property aids in fast access
> during system call filtering as read access is lockless.
>
> Updating the pointer from another task, however, opens up race
> conditions. To allow cross-thread filter pointer updates, writes to the
> seccomp fields are now protected by the sighand spinlock (which is shared
> by all threads in the thread group). Read access remains lockless because
> pointer updates themselves are atomic. However, writes (or cloning)
> often entail additional checking (like maximum instruction counts)
> which require locking to perform safely.
>
> In the case of cloning threads, the child is invisible to the system
> until it enters the task list. To make sure a child can't be cloned from
> a thread and left in a prior state, seccomp duplication is additionally
> moved under the sighand lock. Then parent and child are certain have
> the same seccomp state when they exit the lock.
>
> Based on patches by Will Drewry and David Drysdale.
>
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> Reviewed-by: Oleg Nesterov <oleg@xxxxxxxxxx>
> Reviewed-by: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
>
> +------------------------------------------+------------+------------+------------+
> | | c8bee430dc | dbd952127d | c2426d2ad5 |
> +------------------------------------------+------------+------------+------------+
> | boot_successes | 60 | 0 | 0 |
> | boot_failures | 0 | 20 | 11 |
> | kernel_BUG_at_kernel/fork.c | 0 | 20 | 11 |
> | invalid_opcode | 0 | 20 | 11 |
> | EIP_is_at_copy_process | 0 | 20 | 11 |
> | Kernel_panic-not_syncing:Fatal_exception | 0 | 20 | 11 |
> | backtrace:do_fork | 0 | 20 | 11 |
> +------------------------------------------+------------+------------+------------+
>
> [ 0.023060] CPU: Intel Core Processor (Haswell) (fam: 06, model: 3c, stepping: 01)
> [ 0.046204] ftrace: allocating 39817 entries in 78 pages
> [ 0.070150] ------------[ cut here ]------------
> [ 0.071335] kernel BUG at kernel/fork.c:1102!
> [ 0.072727] invalid opcode: 0000 [#1] PREEMPT
> [ 0.074202] CPU: 0 PID: 0 Comm: swapper Not tainted 3.16.0-rc5-00031-gdbd95212 #339
> [ 0.076276] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
> [ 0.077594] task: c2832140 ti: c2826000 task.ti: c2826000
> [ 0.078816] EIP: 0060:[<c1073080>] EFLAGS: 00210046 CPU: 0
> [ 0.080000] EIP is at copy_process+0x1720/0x1860
> [ 0.080000] EAX: 00000003 EBX: d3464000 ECX: 00000000 EDX: 00000000
> [ 0.080000] ESI: fffffff4 EDI: d34701f0 EBP: c2827f84 ESP: c2827f54
> [ 0.080000] DS: 007b ES: 007b FS: 0000 GS: 0000 SS: 0068
> [ 0.080000] CR0: 80050033 CR2: ffffffff CR3: 02c1e000 CR4: 00040690
> [ 0.080000] Stack:
> [ 0.080000] d3464000 c2827fb8 00000000 00000000 c2457150 00000000 00000000 00800300
> [ 0.080000] fffffff4 c2457150 00020800 c2c1f800 c2827fb8 c1073386 00000000 d3407280
> [ 0.080000] 00000000 00800300 c24780f5 00000000 00009b89 00000000 c2457150 00020800
> [ 0.080000] Call Trace:
> [ 0.080000] [<c2457150>] ? rest_init+0x110/0x110
> [ 0.080000] [<c2457150>] ? rest_init+0x110/0x110
> [ 0.080000] [<c1073386>] do_fork+0x86/0x710
> [ 0.080000] [<c24780f5>] ? smp_trace_apic_timer_interrupt+0x5/0x2a6
> [ 0.080000] [<c2457150>] ? rest_init+0x110/0x110
> [ 0.080000] [<c1073a4b>] kernel_thread+0x3b/0x50
> [ 0.080000] [<c245707b>] rest_init+0x3b/0x110
> [ 0.080000] [<c2acc562>] start_kernel+0x864/0x88a
> [ 0.080000] [<c2acb31b>] i386_start_kernel+0xe9/0xfb
> [ 0.080000] Code: 00 83 05 f8 d1 c5 c2 01 83 15 fc d1 c5 c2 00 83 05 00 d2 c5 c2 01 83 15 04 d2 c5 c2 00 83 05 e0 cf c5 c2 01 83 15 e4 cf c5 c2 00 <0f> 0b 83 05 e8 cf c5 c2 01 83 15 ec cf c5 c2 00 8b 45 e4 83 05
> [ 0.080000] EIP: [<c1073080>] copy_process+0x1720/0x1860 SS:ESP 0068:c2827f54
> [ 0.080000] ---[ end trace 8262cf1029187723 ]---
> [ 0.080000] Kernel panic - not syncing: Fatal exception
>
> git bisect start 594081ee7145cc30a3977cb4e218f81213b63dc5 v3.16 --
> git bisect bad b49e1043c48dac23f64fba684d31c4a96c1ffaa0 # 19:15 0- 2 tpm: Properly clean sysfs entries in error path
> git bisect good 32c2e6752ff0f48fe03b9e1c7c64bde580a840d2 # 20:28 20+ 0 ima: provide double buffering for hash calculation
> git bisect bad 7d8b6c63751cfbbe5eef81a48c22978b3407a3ad # 20:46 0- 1 CAPABILITIES: remove undefined caps from all processes
> git bisect bad fd33c43677a7965624b46352a686a7c1e72ae4aa # 21:31 0- 2 Merge tag 'seccomp-3.17' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux into next
> git bisect good 2ccf4661f315615d018686d91d030a94001d0cc6 # 22:14 20+ 0 Merge branch 'next' of git://git.infradead.org/users/pcmoore/selinux into next
> git bisect good 839669714f0a85d677283690e6e164fb698ce206 # 22:31 20+ 0 ARM: add seccomp syscall
> git bisect good c8bee430dc52cfca6c1aab27752a89275d78d50f # 22:43 20+ 0 seccomp: split filter prep from check and apply
> git bisect bad 3ba2530cc06eb4aee4f1f754f43d781e8a12ee09 # 22:48 0- 19 seccomp: allow mode setting across threads
> git bisect bad dbd952127d11bb44a4ea30b08cc60531b6a23d71 # 23:16 0- 20 seccomp: introduce writer locking
> # first bad commit: [dbd952127d11bb44a4ea30b08cc60531b6a23d71] seccomp: introduce writer locking
> git bisect good c8bee430dc52cfca6c1aab27752a89275d78d50f # 23:18 60+ 0 seccomp: split filter prep from check and apply
> git bisect good a1cff6e25e6e3b55183610dddca91546951b20e3 # 23:27 60+ 0 Merge branch 'fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/evalenti/linux-soc-thermal
>
>
> This script may reproduce the error.
>
> ----------------------------------------------------------------------------
> #!/bin/bash
>
> kernel=$1
>
> kvm=(
> qemu-system-x86_64
> -enable-kvm
> -cpu Haswell,+smep,+smap
> -kernel $kernel
> -m 320
> -smp 1
> -net nic,vlan=1,model=e1000
> -net user,vlan=1
> -boot order=nc
> -no-reboot
> -watchdog i6300esb
> -rtc base=localtime
> -serial stdio
> -display none
> -monitor null
> )
>
> append=(
> hung_task_panic=1
> earlyprintk=ttyS0,115200
> debug
> apic=debug
> sysrq_always_enabled
> rcupdate.rcu_cpu_stall_timeout=100
> panic=-1
> softlockup_panic=1
> nmi_watchdog=panic
> oops=panic
> load_ramdisk=2
> prompt_ramdisk=0
> console=ttyS0,115200
> console=tty0
> vga=normal
> root=/dev/ram0
> rw
> drbd.minor_count=8
> )
>
> "${kvm[@]}" --append "${append[*]}"
> ----------------------------------------------------------------------------
>
> Thanks,
> Fengguang
>
> _______________________________________________
> LKP mailing list
> LKP@xxxxxxxxxxxxxxx
>
--
Kees Cook
Chrome OS Security
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