divide error in nbd_ioctl

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    217c3e019675 disable stringop truncation warnings for now
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13665da6400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=531a917630d2a492
dashboard link: https://syzkaller.appspot.com/bug?extid=25dbecbec1e62c6b0dd4
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=163e910a400000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=169dfe0a400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+25dbecbec1e62c6b0dd4@xxxxxxxxxxxxxxxxxxxxxxxxx

random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
divide error: 0000 [#1] SMP KASAN
CPU: 0 PID: 4667 Comm: syz-executor024 Not tainted 4.19.0-rc1+ #216
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
RIP: 0010:div_s64_rem include/linux/math64.h:41 [inline]
RIP: 0010:div_s64 include/linux/math64.h:139 [inline]
RIP: 0010:__nbd_ioctl drivers/block/nbd.c:1242 [inline]
RIP: 0010:nbd_ioctl+0x53c/0xcf0 drivers/block/nbd.c:1303
Code: ea 03 80 3c 02 00 0f 85 1c 07 00 00 48 8b b5 c0 fe ff ff 48 63 8d b8  
fe ff ff 48 8b 86 c8 00 00 00 48 8d be c0 00 00 00 48 99 <48> f7 f9 48 ba  
00 00 00 00 00 fc ff df 48 89 f9 48 c1 e9 03 80 3c
RSP: 0018:ffff8801c90bf828 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 0000000000000001 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffff8801ccb23c00 RDI: ffff8801ccb23cc0
RBP: ffff8801c90bf9a0 R08: ffff8801bc502640 R09: ffffed003a62d01d
R10: ffff8801c90bf818 R11: ffff8801d31680ef R12: ffff8801d3168000
R13: 00000000ffffffe7 R14: ffff8801d31680e0 R15: ffff8801d5730840
FS:  00000000015b2880(0000) GS:ffff8801db000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000000043e560 CR3: 00000001b8034000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 __blkdev_driver_ioctl block/ioctl.c:303 [inline]
 blkdev_ioctl+0x9cd/0x2030 block/ioctl.c:601
 block_ioctl+0xee/0x130 fs/block_dev.c:1883
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:501 [inline]
 do_vfs_ioctl+0x1de/0x1720 fs/ioctl.c:685
 ksys_ioctl+0xa9/0xd0 fs/ioctl.c:702
 __do_sys_ioctl fs/ioctl.c:709 [inline]
 __se_sys_ioctl fs/ioctl.c:707 [inline]
 __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:707
 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x443d29
Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 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 0f 83 7b d8 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffe343644d8 EFLAGS: 00000213 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000004002e0 RCX: 0000000000443d29
RDX: 0000000000000000 RSI: 000000000000ab01 RDI: 0000000000000003
RBP: 00000000006ce018 R08: 0000000000000000 R09: 00000000004002e0
R10: 000000000000000f R11: 0000000000000213 R12: 0000000000401a30
R13: 0000000000401ac0 R14: 0000000000000000 R15: 0000000000000000
Modules linked in:
Dumping ftrace buffer:
   (ftrace buffer empty)
---[ end trace 25c60c4714d4e2ee ]---
RIP: 0010:div_s64_rem include/linux/math64.h:41 [inline]
RIP: 0010:div_s64 include/linux/math64.h:139 [inline]
RIP: 0010:__nbd_ioctl drivers/block/nbd.c:1242 [inline]
RIP: 0010:nbd_ioctl+0x53c/0xcf0 drivers/block/nbd.c:1303
Code: ea 03 80 3c 02 00 0f 85 1c 07 00 00 48 8b b5 c0 fe ff ff 48 63 8d b8  
fe ff ff 48 8b 86 c8 00 00 00 48 8d be c0 00 00 00 48 99 <48> f7 f9 48 ba  
00 00 00 00 00 fc ff df 48 89 f9 48 c1 e9 03 80 3c
RSP: 0018:ffff8801c90bf828 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 0000000000000001 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffff8801ccb23c00 RDI: ffff8801ccb23cc0
RBP: ffff8801c90bf9a0 R08: ffff8801bc502640 R09: ffffed003a62d01d
R10: ffff8801c90bf818 R11: ffff8801d31680ef R12: ffff8801d3168000
R13: 00000000ffffffe7 R14: ffff8801d31680e0 R15: ffff8801d5730840
FS:  00000000015b2880(0000) GS:ffff8801db000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000000043e560 CR3: 00000001b8034000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


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