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Subject: Re: divide error in nbd_ioctl
To:     Josef Bacik <josef@toxicpanda.com>
Cc:     syzbot <syzbot+25dbecbec1e62c6b0dd4@syzkaller.appspotmail.com>,
        linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        nbd@other.debian.org, syzkaller-bugs@googlegroups.com
References: <0000000000006105bf057506ebb9@google.com>
 <dc31a6f0-97c6-9dc0-8676-089e9fd69868@kernel.dk>
 <20180904174810.gp7bd5s3kijhjp5d@destiny>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <9571a094-a87f-e6dd-2bdf-f9b4ea500ca9@kernel.dk>
Date:   Tue, 4 Sep 2018 11:55:11 -0600
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On 9/4/18 11:48 AM, Josef Bacik wrote:
> On Tue, Sep 04, 2018 at 09:07:37AM -0600, Jens Axboe wrote:
>> On 9/4/18 1:51 AM, syzbot wrote:
>>> 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@syzkaller.appspotmail.com
>>>
>>> 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
>>
>> Looks like NBD_SET_BLKSIZE is happy to just take whatever value.
>> We should ensure that it's a power of 2, not zero, and bigger
>> or equal than 512, but smaller or equal to PAGE_SIZE. Something
>> like this?
>>
>>
>> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
>> index 3863c00372bb..14a51254c3db 100644
>> --- a/drivers/block/nbd.c
>> +++ b/drivers/block/nbd.c
>> @@ -1239,6 +1239,9 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
>>  	case NBD_SET_SOCK:
>>  		return nbd_add_socket(nbd, arg, false);
>>  	case NBD_SET_BLKSIZE:
>> +		if (!arg || !is_power_of_2(arg) || arg < 512 ||
>> +		    arg > PAGE_SIZE)
>> +			return -EINVAL;
>>  		nbd_size_set(nbd, arg,
>>  			     div_s64(config->bytesize, arg));
>>  		return 0;
> 
> Thanks Jens, you can add
> 
> Reviewed-by: Josef Bacik <josef@toxicpanda.com>

Thanks, applied for 4.19.

-- 
Jens Axboe