linux-kernel - Re: [syzbot] kernel BUG in vhost_get_vq

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Date:   Mon, 21 Feb 2022 14:09:26 +0100
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     syzbot <syzbot+3140b17cb44a7b174008@...kaller.appspotmail.com>
Cc:     hdanton@...a.com, jasowang@...hat.com,
        linux-kernel@...r.kernel.org, mst@...hat.com,
        syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] kernel BUG in vhost_get_vq_desc

It seems that this patch [1] should fix also this issue. (syzbot seems 
happy).

I think because we didn't set the backed to NULL, the worker kept 
running and messing up.

Stefano

[1] 
https://lore.kernel.org/virtualization/20220221114916.107045-1-sgarzare@redhat.com/T/#u

On Sat, Feb 19, 2022 at 05:01:10AM -0800, syzbot wrote:
>Hello,
>
>syzbot has tested the proposed patch but the reproducer is still triggering an issue:
>kernel BUG in vhost_get_vq_desc
>
>------------[ cut here ]------------
>kernel BUG at drivers/vhost/vhost.c:2338!
>invalid opcode: 0000 [#1] PREEMPT SMP KASAN
>CPU: 0 PID: 4071 Comm: vhost-4070 Not tainted 5.17.0-rc4-syzkaller-00054-gf71077a4d84b-dirty #0
>Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
>RIP: 0010:vhost_get_vq_desc+0x1dc5/0x2350 drivers/vhost/vhost.c:2338
>Code: 00 00 00 48 c7 c6 20 2c 9d 8a 48 c7 c7 98 a6 8e 8d 48 89 ca 48 c1 e1 04 48 01 d9 e8 25 59 28 fd e9 74 ff ff ff e8 cb c7 a1 fa <0f> 0b e8 c4 c7 a1 fa 48 8b 54 24 18 48 b8 00 00 00 00 00 fc ff df
>RSP: 0018:ffffc900028bfb78 EFLAGS: 00010293
>RAX: 0000000000000000 RBX: 0000000000000001 RCX: 0000000000000000
>RDX: ffff88801cbd1d00 RSI: ffffffff86d71655 RDI: 0000000000000003
>RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000001
>R10: ffffffff86d7072d R11: 0000000000000000 R12: 0000000000000000
>R13: 0000000000000000 R14: ffff88806ffc4bb0 R15: dffffc0000000000
>FS:  0000000000000000(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000
>CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>CR2: 0000000000000002 CR3: 000000001d077000 CR4: 00000000003506f0
>DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>Call Trace:
> <TASK>
> vhost_vsock_handle_tx_kick+0x277/0xa20 drivers/vhost/vsock.c:522
> vhost_worker+0x2e9/0x3e0 drivers/vhost/vhost.c:374
> kthread+0x2e9/0x3a0 kernel/kthread.c:377
> ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
> </TASK>
>Modules linked in:
>---[ end trace 0000000000000000 ]---
>RIP: 0010:vhost_get_vq_desc+0x1dc5/0x2350 drivers/vhost/vhost.c:2338
>Code: 00 00 00 48 c7 c6 20 2c 9d 8a 48 c7 c7 98 a6 8e 8d 48 89 ca 48 c1 e1 04 48 01 d9 e8 25 59 28 fd e9 74 ff ff ff e8 cb c7 a1 fa <0f> 0b e8 c4 c7 a1 fa 48 8b 54 24 18 48 b8 00 00 00 00 00 fc ff df
>RSP: 0018:ffffc900028bfb78 EFLAGS: 00010293
>RAX: 0000000000000000 RBX: 0000000000000001 RCX: 0000000000000000
>RDX: ffff88801cbd1d00 RSI: ffffffff86d71655 RDI: 0000000000000003
>RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000001
>R10: ffffffff86d7072d R11: 0000000000000000 R12: 0000000000000000
>R13: 0000000000000000 R14: ffff88806ffc4bb0 R15: dffffc0000000000
>FS:  0000000000000000(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000
>CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>CR2: 00007fc7293991d0 CR3: 000000001d077000 CR4: 00000000003506e0
>DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>
>
>Tested on:
>
>commit:         f71077a4 Merge tag 'mmc-v5.17-rc1-2' of git://git.kern..
>git tree:       https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/
>console output: https://syzkaller.appspot.com/x/log.txt?x=11e82d7a700000
>kernel config:  https://syzkaller.appspot.com/x/.config?x=a78b064590b9f912
>dashboard link: https://syzkaller.appspot.com/bug?extid=3140b17cb44a7b174008
>compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
>patch:          https://syzkaller.appspot.com/x/patch.diff?x=11857326700000
>