Date:   Sun, 11 Apr 2021 09:10:37 +0100
From:   Pavel Begunkov <asml.silence@...il.com>
To:     Hao Sun <sunhao.th@...il.com>, axboe@...nel.dk,
        io-uring@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org
Subject: Re: BUG: unable to handle kernel NULL pointer dereference in
 io_uring_cancel_task_requests

On 11/04/2021 04:08, Hao Sun wrote:
> Hi
> 
> When using Healer(https://github.com/SunHao-0/healer/tree/dev) to fuzz
> the Linux kernel, I found a null-ptr-deref bug in
> io_uring_cancel_task_requests under fault injection condition, but I'm
> not sure about this.
> Sorry, I do not have a reproducing program for this bug.
> I hope that the stack trace information in the crash log can help you
> locate the problem.

Thanks Hao. io_cqring_wait() fails should not anyhow affect
cancellation, so the log doesn't make sense from first sight,
something strange is going on.

> 
> Here is the details:
> commit:   3b9cdafb5358eb9f3790de2f728f765fef100731
> version:   linux 5.11
> git tree:    upstream
> Full log can be found in the attachment.
> cqwait()
> Fault injection log:
> FAULT_INJECTION: forcing a failure.
> name fail_usercopy, interval 1, probability 0, space 0, times 0
> CPU: 1 PID: 9161 Comm: executor Not tainted 5.11.0+ #5
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
> rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu.org 04/01/2014
> Call Trace:
>  __dump_stack lib/dump_stack.c:79 [inline]
>  dump_stack+0x137/0x194 lib/dump_stack.c:120
>  fail_dump lib/fault-inject.c:52 [inline]
>  should_fail+0x23e/0x250 lib/fault-inject.c:146
>  should_fail_usercopy+0x16/0x20 lib/fault-inject-usercopy.c:37
>  _copy_from_user+0x1c/0xd0 lib/usercopy.c:14
>  copy_from_user include/linux/uaccess.h:192 [inline]
>  set_user_sigmask+0x4b/0x110 kernel/signal.c:3015
>  io_cqring_wait+0x2e3/0x8b0 fs/io_uring.c:7250
>  __do_sys_io_uring_enter fs/io_uring.c:9480 [inline]
>  __se_sys_io_uring_enter+0x8fc/0xb70 fs/io_uring.c:9397
>  __x64_sys_io_uring_enter+0x74/0x80 fs/io_uring.c:9397
>  do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
>  entry_SYSCALL_64_after_hwframe+0x44/0xae
> RIP: 0033:0x46a379
> Code: f7 d8 64 89 02 b8 ff ff ff ff c3 66 0f 1f 44 00 00 48 89 f8 48
> 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d
> 01 f0 ff ff 73 01 c3 48 c7 c1 bc ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007f046fa19c58 EFLAGS: 00000246 ORIG_RAX: 00000000000001aa
> RAX: ffffffffffffffda RBX: 000000000078c080 RCX: 000000000046a379
> RDX: 00000000000066ab RSI: 0000000000000001 RDI: 0000000000000003
> RBP: 00007f046fa19c90 R08: 0000000020000040 R09: 0000000000000008
> R10: 0000000000000003 R11: 0000000000000246 R12: 0000000000000000
> R13: 0000000000000000 R14: 000000000078c080 R15: 00007fff769deef0
> 
> Crash log:
> BUG: kernel NULL pointer dereference, address: 0000000000000040
> #PF: supervisor read access in kernel mode
> #PF: error_code(0x0000) - not-present page
> PGD 49954067 P4D 49954067 PUD 45f92067 PMD 0
> Oops: 0000 [#1] PREEMPT SMP
> CPU: 1 PID: 9161 Comm: executor Not tainted 5.11.0+ #5
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
> rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu.org 04/01/2014
> RIP: 0010:io_uring_cancel_task_requests+0x3f/0x990 fs/io_uring.c:9045
> Code: 48 8b 04 25 28 00 00 00 48 89 44 24 68 e8 89 e6 c5 ff 65 4c 8b
> 34 25 00 6d 01 00 49 8d 7c 24 40 48 89 7c 24 30 e8 81 97 d6 ff <41> 8b
> 5c 24 40 89 de 83 e6 02 31 ff e8 70 ea c5 ff 83 e3 02 48 89
> RSP: 0018:ffffc90002a97b48 EFLAGS: 00010246
> RAX: ffff88804b8e0d38 RBX: ffff88804b8ad700 RCX: 0000000000000764
> RDX: 0000000000000040 RSI: ffff8880409d5140 RDI: 0000000000000040
> RBP: ffff8880409d5140 R08: 0000000000000000 R09: 0000000000000043
> R10: 0001ffffffffffff R11: ffff88804b8e0280 R12: 0000000000000000
> R13: ffff8880409d5140 R14: ffff88804b8e0280 R15: ffff8880481c1800
> FS:  00007f046fa1a700(0000) GS:ffff88807ec00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000000000040 CR3: 00000000479a5000 CR4: 0000000000750ee0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> PKRU: 55555554
> Call Trace:
>  __io_uring_files_cancel+0x9b/0x200 fs/io_uring.c:9140
>  io_uring_files_cancel include/linux/io_uring.h:65 [inline]
>  do_exit+0x1a8/0x16d0 kernel/exit.c:780
>  do_group_exit+0xc5/0x180 kernel/exit.c:922
>  get_signal+0xd90/0x1470 kernel/signal.c:2773
>  arch_do_signal_or_restart+0x2a/0x260 arch/x86/kernel/signal.c:811
>  handle_signal_work kernel/entry/common.c:147 [inline]
>  exit_to_user_mode_loop kernel/entry/common.c:171 [inline]
>  exit_to_user_mode_prepare+0x109/0x1a0 kernel/entry/common.c:208
>  __syscall_exit_to_user_mode_work kernel/entry/common.c:290 [inline]
>  syscall_exit_to_user_mode+0x20/0x40 kernel/entry/common.c:301
>  do_syscall_64+0x45/0x80 arch/x86/entry/common.c:56
>  entry_SYSCALL_64_after_hwframe+0x44/0xae
> RIP: 0033:0x46a379
> Code: f7 d8 64 89 02 b8 ff ff ff ff c3 66 0f 1f 44 00 00 48 89 f8 48
> 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d
> 01 f0 ff ff 73 01 c3 48 c7 c1 bc ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007f046fa19cd8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
> RAX: fffffffffffffe00 RBX: 000000000078c080 RCX: 000000000046a379
> RDX: 0000000000000000 RSI: 0000000000000080 RDI: 000000000078c088
> RBP: 000000000078c088 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 000000000078c08c
> R13: 0000000000000000 R14: 000000000078c080 R15: 00007fff769deef0
> Modules linked in:
> Dumping ftrace buffer:
>    (ftrace buffer empty)
> CR2: 0000000000000040
> ---[ end trace 613db1a25ecf6443 ]---
> RIP: 0010:io_uring_cancel_task_requests+0x3f/0x990 fs/io_uring.c:9045
> Code: 48 8b 04 25 28 00 00 00 48 89 44 24 68 e8 89 e6 c5 ff 65 4c 8b
> 34 25 00 6d 01 00 49 8d 7c 24 40 48 89 7c 24 30 e8 81 97 d6 ff <41> 8b
> 5c 24 40 89 de 83 e6 02 31 ff e8 70 ea c5 ff 83 e3 02 48 89
> RSP: 0018:ffffc90002a97b48 EFLAGS: 00010246
> RAX: ffff88804b8e0d38 RBX: ffff88804b8ad700 RCX: 0000000000000764
> RDX: 0000000000000040 RSI: ffff8880409d5140 RDI: 0000000000000040
> RBP: ffff8880409d5140 R08: 0000000000000000 R09: 0000000000000043
> R10: 0001ffffffffffff R11: ffff88804b8e0280 R12: 0000000000000000
> R13: ffff8880409d5140 R14: ffff88804b8e0280 R15: ffff8880481c1800
> FS:  00007f046fa1a700(0000) GS:ffff88807ec00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000000000040 CR3: 00000000479a5000 CR4: 0000000000750ee0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> PKRU: 55555554
> 

-- 
Pavel Begunkov

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