Re: BUG: unable to handle kernel NULL pointer dereference in wait_consider_task

[Wei Chen]

Dear Linux developers,

This crash persists in the latest commit, v5.15.76 (4f5365f77018).
However, I still cannot find a reproducer for the crash. I hope the
following crash report is helpful to you.

BUG: kernel NULL pointer dereference, address: 0000000000000850
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 114818067 P4D 114818067 PUD 114819067 PMD 0
Oops: 0000 [#1] PREEMPT SMP
CPU: 1 PID: 6550 Comm: syz-executor.0 Not tainted 5.15.76 #5
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
rel-1.13.0-48-gd9c812dda519-prebuilt.qemu.org 04/01/2014
RIP: 0010:ptrace_reparented include/linux/ptrace.h:92 [inline]
RIP: 0010:wait_consider_task+0xb1b/0x1250 kernel/exit.c:1320
Code: 5b 28 09 01 e9 ad f7 ff ff e8 21 d5 14 00 48 8b 45 b8 c7 40 50
00 00 00 00 e9 7a f5 ff ff e8 0c d5 14 00 48 8b 83 98 05 00 00 <4c> 8b
b0 50 08 00 00 48 8b 83 a0 05 00 00 4c 8b b8 50 08 00 00 31
RSP: 0018:ffffc90000ccbd08 EFLAGS: 00010293
RAX: 0000000000000000 RBX: ffff88811084d340 RCX: 0000000000000000
RDX: ffff888014289bc0 RSI: ffffffff81234b74 RDI: ffffc90000ccbdc0
RBP: ffffc90000ccbd70 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000020 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000040000005 R15: ffffffff81235380
FS:  00000000018e7940(0000) GS:ffff88813dc00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000850 CR3: 0000000114817000 CR4: 00000000003506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 do_wait_thread kernel/exit.c:1397 [inline]
 do_wait+0x253/0x510 kernel/exit.c:1514
 kernel_wait4+0xb3/0x190 kernel/exit.c:1677
 __do_sys_wait4+0xce/0xe0 kernel/exit.c:1705
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x34/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x61/0xcb
RIP: 0033:0x418fea
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:00007fff47940a40 EFLAGS: 00000246 ORIG_RAX: 000000000000003d
RAX: ffffffffffffffda RBX: 00000000ffffffff RCX: 0000000000418fea
RDX: 0000000040000001 RSI: 00007fff47940acc RDI: 00000000ffffffff
RBP: 00007fff47940acc R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000040000001
R13: 0000000000000032 R14: 00007fff47940acc R15: 0000000000000001
 </TASK>
Modules linked in:
CR2: 0000000000000850
---[ end trace 3c86ff94252062e2 ]---
RIP: 0010:ptrace_reparented include/linux/ptrace.h:92 [inline]
RIP: 0010:wait_consider_task+0xb1b/0x1250 kernel/exit.c:1320
Code: 5b 28 09 01 e9 ad f7 ff ff e8 21 d5 14 00 48 8b 45 b8 c7 40 50
00 00 00 00 e9 7a f5 ff ff e8 0c d5 14 00 48 8b 83 98 05 00 00 <4c> 8b
b0 50 08 00 00 48 8b 83 a0 05 00 00 4c 8b b8 50 08 00 00 31
RSP: 0018:ffffc90000ccbd08 EFLAGS: 00010293
RAX: 0000000000000000 RBX: ffff88811084d340 RCX: 0000000000000000
RDX: ffff888014289bc0 RSI: ffffffff81234b74 RDI: ffffc90000ccbdc0
RBP: ffffc90000ccbd70 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000020 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000040000005 R15: ffffffff81235380
FS:  00000000018e7940(0000) GS:ffff88813dc00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000850 CR3: 0000000114817000 CR4: 00000000003506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess), 2 bytes skipped:
   0: 09 01                or     %eax,(%rcx)
   2: e9 ad f7 ff ff        jmpq   0xfffff7b4
   7: e8 21 d5 14 00        callq  0x14d52d
   c: 48 8b 45 b8          mov    -0x48(%rbp),%rax
  10: c7 40 50 00 00 00 00 movl   $0x0,0x50(%rax)
  17: e9 7a f5 ff ff        jmpq   0xfffff596
  1c: e8 0c d5 14 00        callq  0x14d52d
  21: 48 8b 83 98 05 00 00 mov    0x598(%rbx),%rax
* 28: 4c 8b b0 50 08 00 00 mov    0x850(%rax),%r14 <-- trapping instruction
  2f: 48 8b 83 a0 05 00 00 mov    0x5a0(%rbx),%rax
  36: 4c 8b b8 50 08 00 00 mov    0x850(%rax),%r15
  3d: 31                    .byte 0x31

Best,
Wei



On Sun, 30 Oct 2022 at 17:43, Wei Chen <harperchen1110@xxxxxxxxx> wrote:
>
> 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