Re: general protection fault in finish_task_switch (2)

[syzbot <syzbot+1f56df64bfb3c29dde6f@syzkaller.appspotmail.com>]

syzbot has found a reproducer for the following crash on:

HEAD commit:    778a33959a8a Merge tag 'please-pull-noboot' of git://git.k..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14a5385a400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=214e4990bd49329f
dashboard link: https://syzkaller.appspot.com/bug?extid=1f56df64bfb3c29dde6f
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
userspace arch: i386
syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=13ffa561400000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10023961400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+1f56df64bfb3c29dde6f@syzkaller.appspotmail.com

random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
L1TF CPU bug present and SMT on, data leak possible. See CVE-2018-3646 and  
https://www.kernel.org/doc/html/latest/admin-guide/l1tf.html for details.
kasan: CONFIG_KASAN_INLINE enabled
kasan: GPF could be caused by NULL-ptr deref or user memory access
general protection fault: 0000 [#1] SMP KASAN
CPU: 0 PID: 4489 Comm: syz-executor233 Not tainted 4.18.0+ #103
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
RIP: 0010:__fire_sched_in_preempt_notifiers kernel/sched/core.c:2481  
[inline]
RIP: 0010:fire_sched_in_preempt_notifiers kernel/sched/core.c:2487 [inline]
RIP: 0010:finish_task_switch+0x538/0x870 kernel/sched/core.c:2679
Code: 89 e1 48 c1 e9 03 42 80 3c 39 00 0f 85 ab 01 00 00 4d 8b 24 24 4d 85  
e4 0f 84 e3 fc ff ff 49 8d 7c 24 10 48 89 f9 48 c1 e9 03 <42> 80 3c 39 00  
74 a5 e8 8c a5 67 00 eb 9e 80 3d 8b c3 32 07 00 0f
RSP: 0018:ffff8801ac0ff058 EFLAGS: 00010a06
RAX: 0000000000000000 RBX: ffff8801db02cc40 RCX: 1bd5a00000000022
RDX: 0000000000000000 RSI: ffffffff810ed162 RDI: dead000000000110
RBP: ffff8801ac0ff140 R08: ffff8801acb8c300 R09: ffffed003b221b6c
R10: ffffed003b221b6c R11: ffff8801d910db67 R12: dead000000000100
R13: ffff8801ca5e0040 R14: 0000000000000000 R15: dffffc0000000000
FS:  0000000000000000(0000) GS:ffff8801db000000(0063) knlGS:00000000f7f07b40
CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: 00007f1304e0b000 CR3: 00000001acab3000 CR4: 00000000001426f0
Call Trace:
  context_switch kernel/sched/core.c:2826 [inline]
  __schedule+0x884/0x1df0 kernel/sched/core.c:3471
  schedule+0xfb/0x450 kernel/sched/core.c:3515
  freezable_schedule include/linux/freezer.h:172 [inline]
  futex_wait_queue_me+0x3f9/0x840 kernel/futex.c:2530
  futex_wait+0x45b/0xa20 kernel/futex.c:2645
  do_futex+0x336/0x27d0 kernel/futex.c:3527
  __do_compat_sys_futex kernel/futex_compat.c:201 [inline]
  __se_compat_sys_futex kernel/futex_compat.c:175 [inline]
  __ia32_compat_sys_futex+0x3d9/0x5f0 kernel/futex_compat.c:175
  do_syscall_32_irqs_on arch/x86/entry/common.c:326 [inline]
  do_fast_syscall_32+0x34d/0xfb2 arch/x86/entry/common.c:397
  entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139
RIP: 0023:0xf7f0bca9
Code: 55 08 8b 88 64 cd ff ff 8b 98 68 cd ff ff 89 c8 85 d2 74 02 89 0a 5b  
5d c3 8b 04 24 c3 8b 1c 24 c3 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90  
90 90 90 eb 0d 90 90 90 90 90 90 90 90 90 90 90 90
RSP: 002b:00000000f7f071ec EFLAGS: 00000296 ORIG_RAX: 00000000000000f0
RAX: ffffffffffffffda RBX: 00000000080fb008 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000005
RBP: 00000000c080aebe R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
Modules linked in:
Dumping ftrace buffer:
    (ftrace buffer empty)
---[ end trace a4bb2f1beb6735f0 ]---
RIP: 0010:__fire_sched_in_preempt_notifiers kernel/sched/core.c:2481  
[inline]
RIP: 0010:fire_sched_in_preempt_notifiers kernel/sched/core.c:2487 [inline]
RIP: 0010:finish_task_switch+0x538/0x870 kernel/sched/core.c:2679
Code: 89 e1 48 c1 e9 03 42 80 3c 39 00 0f 85 ab 01 00 00 4d 8b 24 24 4d 85  
e4 0f 84 e3 fc ff ff 49 8d 7c 24 10 48 89 f9 48 c1 e9 03 <42> 80 3c 39 00  
74 a5 e8 8c a5 67 00 eb 9e 80 3d 8b c3 32 07 00 0f
RSP: 0018:ffff8801ac0ff058 EFLAGS: 00010a06
RAX: 0000000000000000 RBX: ffff8801db02cc40 RCX: 1bd5a00000000022
RDX: 0000000000000000 RSI: ffffffff810ed162 RDI: dead000000000110
RBP: ffff8801ac0ff140 R08: ffff8801acb8c300 R09: ffffed003b221b6c
R10: ffffed003b221b6c R11: ffff8801d910db67 R12: dead000000000100
R13: ffff8801ca5e0040 R14: 0000000000000000 R15: dffffc0000000000
FS:  0000000000000000(0000) GS:ffff8801db000000(0063) knlGS:00000000f7f07b40
CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: 00007f1304e0b000 CR3: 00000001acab3000 CR4: 00000000001426f0