linux-kernel - general protection fault in start

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Message-ID: <CANX2M5ZGXGq0UV=Ycv8JpserFwP4BNkf2zEgLxrAoh0wjWGWTw@mail.gmail.com>
Date:   Fri, 22 Jul 2022 13:40:44 -0700
From:   Dipanjan Das <mail.dipanjan.das@...il.com>
To:     efremov@...ux.com, axboe@...nel.dk, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     syzkaller@...glegroups.com, fleischermarius@...glemail.com,
        its.priyanka.bose@...il.com
Subject: general protection fault in start_motor

Hi,

We would like to report the following bug which has been found by our
modified version of syzkaller.

======================================================
description: general protection fault in start_motor
affected file: drivers/block/floppy.c
kernel version: 5.10.131
kernel commit: de62055f423f5dcb548f74cebd68f03c8903f73a
git tree: upstream
kernel config: https://syzkaller.appspot.com/x/.config?x=e49433cfed49b7d9
crash reproducer: attached
======================================================
Crash log:
======================================================
general protection fault, probably for non-canonical address
0xdffffc0000000000: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
CPU: 0 PID: 8820 Comm: kworker/u4:48 Tainted: G           OE     5.10.131+ #3
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
1.13.0-1ubuntu1.1 04/01/2014
Workqueue: floppy fd_timer_workfn
RIP: 0010:start_motor+0x3a/0x3f0 drivers/block/floppy.c:1905
Code: 08 e8 4a 15 1c fd 48 8b 1d 03 30 4d 0b 48 b8 00 00 00 00 00 fc
ff df 0f b6 2d 72 22 4d 0b 48 89 da 48 c1 ea 03 89 e9 41 89 ed <0f> b6
04 02 83 e1 03 41 83 e5 03 84 c0 74 08 3c 03 0f 8e be 02 00
RSP: 0018:ffffc90000a47cc0 EFLAGS: 00010246
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff845483d6 RDI: ffffffff84549f90
RBP: 0000000000000000 R08: ffff88803a2b1ac0 R09: fffffbfff19dad22
R10: 0000000000000000 R11: 0000000000000000 R12: ffffffff84549f90
R13: 0000000000000000 R14: ffff88810c148000 R15: ffff888100069800
FS:  0000000000000000(0000) GS:ffff88811a000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b2fb22000 CR3: 000000002daa9001 CR4: 0000000000170ef0
Call Trace:
 floppy_ready+0x7f/0x1950 drivers/block/floppy.c:1932
 process_one_work+0x953/0x15c0 kernel/workqueue.c:2279
 worker_thread+0x96/0xe20 kernel/workqueue.c:2425
 kthread+0x374/0x490 kernel/kthread.c:313
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296
Modules linked in: uio_ivshmem(OE) uio(E)
---[ end trace 345300e45e5eb538 ]---
RIP: 0010:start_motor+0x3a/0x3f0 drivers/block/floppy.c:1905
Code: 08 e8 4a 15 1c fd 48 8b 1d 03 30 4d 0b 48 b8 00 00 00 00 00 fc
ff df 0f b6 2d 72 22 4d 0b 48 89 da 48 c1 ea 03 89 e9 41 89 ed <0f> b6
04 02 83 e1 03 41 83 e5 03 84 c0 74 08 3c 03 0f 8e be 02 00
RSP: 0018:ffffc90000a47cc0 EFLAGS: 00010246
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff845483d6 RDI: ffffffff84549f90
RBP: 0000000000000000 R08: ffff88803a2b1ac0 R09: fffffbfff19dad22
R10: 0000000000000000 R11: 0000000000000000 R12: ffffffff84549f90
R13: 0000000000000000 R14: ffff88810c148000 R15: ffff888100069800
FS:  0000000000000000(0000) GS:ffff88811a000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fee2b352038 CR3: 00000000425db005 CR4: 0000000000170ef0
----------------
Code disassembly (best guess):
   0: 08 e8                or     %ch,%al
   2: 4a 15 1c fd 48 8b    rex.WX adc $0xffffffff8b48fd1c,%rax
   8: 1d 03 30 4d 0b        sbb    $0xb4d3003,%eax
   d: 48 b8 00 00 00 00 00 movabs $0xdffffc0000000000,%rax
  14: fc ff df
  17: 0f b6 2d 72 22 4d 0b movzbl 0xb4d2272(%rip),%ebp        # 0xb4d2290
  1e: 48 89 da              mov    %rbx,%rdx
  21: 48 c1 ea 03          shr    $0x3,%rdx
  25: 89 e9                mov    %ebp,%ecx
  27: 41 89 ed              mov    %ebp,%r13d
* 2a: 0f b6 04 02          movzbl (%rdx,%rax,1),%eax <-- trapping instruction
  2e: 83 e1 03              and    $0x3,%ecx
  31: 41 83 e5 03          and    $0x3,%r13d
  35: 84 c0                test   %al,%al
  37: 74 08                je     0x41
  39: 3c 03                cmp    $0x3,%al
  3b: 0f                    .byte 0xf
  3c: 8e                    .byte 0x8e
  3d: be                    .byte 0xbe
  3e: 02 00                add    (%rax),%al

-- 
Thanks and Regards,

Dipanjan

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