BUG: unable to handle kernel NULL pointer dereference in wait_consider_task

[Wei Chen]

Dear Linux Developer,

Recently when using our tool to fuzz kernel, the following crash was triggered:

HEAD commit: 64570fbc14f8 Linux 5.15-rc5
git tree: upstream
compiler: gcc 8.0.1
console output:
https://drive.google.com/file/d/1dGe81ZlqkO1khyG9jB9Gr2Wpg47561CV/view?usp=share_link
kernel config: https://drive.google.com/file/d/1uDOeEYgJDcLiSOrx9W8v2bqZ6uOA_55t/view?usp=share_link

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: Wei Chen <harperchen1110@xxxxxxxxx>

BUG: kernel NULL pointer dereference, address: 0000000000000850
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 120603067 P4D 120603067 PUD 120604067 PMD 0
Oops: 0000 [#1] PREEMPT SMP
CPU: 1 PID: 6561 Comm: syz-executor.0 Not tainted 5.15.0-rc5 #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
rel-1.13.0-48-gd9c812dda519-prebuilt.qemu.org 04/01/2014
RIP: 0010:wait_consider_task+0xc74/0x1750
Code: 00 e8 00 e5 34 01 e9 50 f8 ff ff e8 16 b4 16 00 31 f6 31 ff e8
0d b5 16 00 e9 df fc ff ff e8 03 b4 16 00 48 8b 83 98 05 00 00 <4c> 8b
b8 50 08 00 00 48 8b 83 a0 05 00 00 4c 8b b0 50 08 00 00 31
RSP: 0018:ffffc90000ce7d20 EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff888018805280 RCX: ffff888109629b80
RDX: 0000000000000000 RSI: ffff888109629b80 RDI: 0000000000000002
RBP: ffffc90000ce7d90 R08: ffffffff8126bf5d R09: 0000000000000000
R10: 0000000000000005 R11: 0000000000000020 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000020 R15: 0000000040000000
FS:  00000000027bc940(0000) GS:ffff88813dc00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000850 CR3: 0000000120602000 CR4: 00000000003526e0
Call Trace:
 do_wait+0x2ae/0x630
 kernel_wait4+0xff/0x1e0
 __do_sys_wait4+0xd7/0xf0
 do_syscall_64+0x34/0xb0
 entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x4189ea
Code: 41 54 55 41 89 d4 53 48 89 f5 89 fb 48 83 ec 10 e8 6b f6 ff ff
45 31 d2 41 89 c0 44 89 e2 48 89 ee 89 df b8 3d 00 00 00 0f 05 <48> 3d
00 f0 ff ff 77 30 44 89 c7 89 44 24 0c e8 a2 f6 ff ff 8b 44
RSP: 002b:00007ffd6f761890 EFLAGS: 00000246 ORIG_RAX: 000000000000003d
RAX: ffffffffffffffda RBX: 00000000ffffffff RCX: 00000000004189ea
RDX: 0000000040000001 RSI: 00007ffd6f761960 RDI: 00000000ffffffff
RBP: 00007ffd6f761960 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000040000001
R13: 0000000000000001 R14: 0000000000000032 R15: 0000000000000bb8
Modules linked in:
CR2: 0000000000000850
---[ end trace 2e5c6a8b7a712caf ]---
RIP: 0010:wait_consider_task+0xc74/0x1750
Code: 00 e8 00 e5 34 01 e9 50 f8 ff ff e8 16 b4 16 00 31 f6 31 ff e8
0d b5 16 00 e9 df fc ff ff e8 03 b4 16 00 48 8b 83 98 05 00 00 <4c> 8b
b8 50 08 00 00 48 8b 83 a0 05 00 00 4c 8b b0 50 08 00 00 31
RSP: 0018:ffffc90000ce7d20 EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff888018805280 RCX: ffff888109629b80
RDX: 0000000000000000 RSI: ffff888109629b80 RDI: 0000000000000002
RBP: ffffc90000ce7d90 R08: ffffffff8126bf5d R09: 0000000000000000
R10: 0000000000000005 R11: 0000000000000020 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000020 R15: 0000000040000000
FS:  00000000027bc940(0000) GS:ffff88813dc00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000850 CR3: 0000000120602000 CR4: 00000000003526e0
----------------
Code disassembly (best guess):
   0: 00 e8                add    %ch,%al
   2: 00 e5                add    %ah,%ch
   4: 34 01                xor    $0x1,%al
   6: e9 50 f8 ff ff        jmpq   0xfffff85b
   b: e8 16 b4 16 00        callq  0x16b426
  10: 31 f6                xor    %esi,%esi
  12: 31 ff                xor    %edi,%edi
  14: e8 0d b5 16 00        callq  0x16b526
  19: e9 df fc ff ff        jmpq   0xfffffcfd
  1e: e8 03 b4 16 00        callq  0x16b426
  23: 48 8b 83 98 05 00 00 mov    0x598(%rbx),%rax
* 2a: 4c 8b b8 50 08 00 00 mov    0x850(%rax),%r15 <-- trapping instruction
  31: 48 8b 83 a0 05 00 00 mov    0x5a0(%rbx),%rax
  38: 4c 8b b0 50 08 00 00 mov    0x850(%rax),%r14
  3f: 31                    .byte 0x31

Best,
Wei