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Date:   Wed, 6 Mar 2019 09:12:36 +0100
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Adalbert Lazăr <alazar@...defender.com>
Cc:     Stefan Hajnoczi <stefanha@...hat.com>,
        "David S . Miller" <davem@...emloft.net>,
        virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vsock/virtio: fix kernel panic from
 virtio_transport_reset_no_sock

Hi Adalbert,
thanks for catching this issue, I have a comment below.

On Tue, Mar 05, 2019 at 08:01:45PM +0200, Adalbert Lazăr wrote:
> Previous to commit 22b5c0b63f32 ("vsock/virtio: fix kernel panic after device hot-unplug"),
> vsock_core_init() was called from virtio_vsock_probe(). Now,
> virtio_transport_reset_no_sock() can be called before vsock_core_init()
> has the chance to run.
> 
> [Wed Feb 27 14:17:09 2019] BUG: unable to handle kernel NULL pointer dereference at 0000000000000110
> [Wed Feb 27 14:17:09 2019] #PF error: [normal kernel read fault]
> [Wed Feb 27 14:17:09 2019] PGD 0 P4D 0
> [Wed Feb 27 14:17:09 2019] Oops: 0000 [#1] SMP PTI
> [Wed Feb 27 14:17:09 2019] CPU: 3 PID: 59 Comm: kworker/3:1 Not tainted 5.0.0-rc7-390-generic-hvi #390
> [Wed Feb 27 14:17:09 2019] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014
> [Wed Feb 27 14:17:09 2019] Workqueue: virtio_vsock virtio_transport_rx_work [vmw_vsock_virtio_transport]
> [Wed Feb 27 14:17:09 2019] RIP: 0010:virtio_transport_reset_no_sock+0x8c/0xc0 [vmw_vsock_virtio_transport_common]
> [Wed Feb 27 14:17:09 2019] Code: 35 8b 4f 14 48 8b 57 08 31 f6 44 8b 4f 10 44 8b 07 48 8d 7d c8 e8 84 f8 ff ff 48 85 c0 48 89 c3 74 2a e8 f7 31 03 00 48 89 df <48> 8b 80 10 01 00 00 e8 68 fb 69 ed 48 8b 75 f0 65 48 33 34 25 28
> [Wed Feb 27 14:17:09 2019] RSP: 0018:ffffb42701ab7d40 EFLAGS: 00010282
> [Wed Feb 27 14:17:09 2019] RAX: 0000000000000000 RBX: ffff9d79637ee080 RCX: 0000000000000003
> [Wed Feb 27 14:17:09 2019] RDX: 0000000000000001 RSI: 0000000000000002 RDI: ffff9d79637ee080
> [Wed Feb 27 14:17:09 2019] RBP: ffffb42701ab7d78 R08: ffff9d796fae70e0 R09: ffff9d796f403500
> [Wed Feb 27 14:17:09 2019] R10: ffffb42701ab7d90 R11: 0000000000000000 R12: ffff9d7969d09240
> [Wed Feb 27 14:17:09 2019] R13: ffff9d79624e6840 R14: ffff9d7969d09318 R15: ffff9d796d48ff80
> [Wed Feb 27 14:17:09 2019] FS:  0000000000000000(0000) GS:ffff9d796fac0000(0000) knlGS:0000000000000000
> [Wed Feb 27 14:17:09 2019] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [Wed Feb 27 14:17:09 2019] CR2: 0000000000000110 CR3: 0000000427f22000 CR4: 00000000000006e0
> [Wed Feb 27 14:17:09 2019] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [Wed Feb 27 14:17:09 2019] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> [Wed Feb 27 14:17:09 2019] Call Trace:
> [Wed Feb 27 14:17:09 2019]  virtio_transport_recv_pkt+0x63/0x820 [vmw_vsock_virtio_transport_common]
> [Wed Feb 27 14:17:09 2019]  ? kfree+0x17e/0x190
> [Wed Feb 27 14:17:09 2019]  ? detach_buf_split+0x145/0x160
> [Wed Feb 27 14:17:09 2019]  ? __switch_to_asm+0x40/0x70
> [Wed Feb 27 14:17:09 2019]  virtio_transport_rx_work+0xa0/0x106 [vmw_vsock_virtio_transport]
> [Wed Feb 27 14:17:09 2019] NET: Registered protocol family 40
> [Wed Feb 27 14:17:09 2019]  process_one_work+0x167/0x410
> [Wed Feb 27 14:17:09 2019]  worker_thread+0x4d/0x460
> [Wed Feb 27 14:17:09 2019]  kthread+0x105/0x140
> [Wed Feb 27 14:17:09 2019]  ? rescuer_thread+0x360/0x360
> [Wed Feb 27 14:17:09 2019]  ? kthread_destroy_worker+0x50/0x50
> [Wed Feb 27 14:17:09 2019]  ret_from_fork+0x35/0x40
> [Wed Feb 27 14:17:09 2019] Modules linked in: vmw_vsock_virtio_transport vmw_vsock_virtio_transport_common input_leds vsock serio_raw i2c_piix4 mac_hid qemu_fw_cfg autofs4 cirrus ttm drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops virtio_net psmouse drm net_failover pata_acpi virtio_blk failover floppy
> [Wed Feb 27 14:17:09 2019] CR2: 0000000000000110
> [Wed Feb 27 14:17:09 2019] ---[ end trace baa35abd2e040fe5 ]---
> [Wed Feb 27 14:17:09 2019] RIP: 0010:virtio_transport_reset_no_sock+0x8c/0xc0 [vmw_vsock_virtio_transport_common]
> [Wed Feb 27 14:17:09 2019] Code: 35 8b 4f 14 48 8b 57 08 31 f6 44 8b 4f 10 44 8b 07 48 8d 7d c8 e8 84 f8 ff ff 48 85 c0 48 89 c3 74 2a e8 f7 31 03 00 48 89 df <48> 8b 80 10 01 00 00 e8 68 fb 69 ed 48 8b 75 f0 65 48 33 34 25 28
> [Wed Feb 27 14:17:09 2019] RSP: 0018:ffffb42701ab7d40 EFLAGS: 00010282
> [Wed Feb 27 14:17:09 2019] RAX: 0000000000000000 RBX: ffff9d79637ee080 RCX: 0000000000000003
> [Wed Feb 27 14:17:09 2019] RDX: 0000000000000001 RSI: 0000000000000002 RDI: ffff9d79637ee080
> [Wed Feb 27 14:17:09 2019] RBP: ffffb42701ab7d78 R08: ffff9d796fae70e0 R09: ffff9d796f403500
> [Wed Feb 27 14:17:09 2019] R10: ffffb42701ab7d90 R11: 0000000000000000 R12: ffff9d7969d09240
> [Wed Feb 27 14:17:09 2019] R13: ffff9d79624e6840 R14: ffff9d7969d09318 R15: ffff9d796d48ff80
> [Wed Feb 27 14:17:09 2019] FS:  0000000000000000(0000) GS:ffff9d796fac0000(0000) knlGS:0000000000000000
> [Wed Feb 27 14:17:09 2019] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [Wed Feb 27 14:17:09 2019] CR2: 0000000000000110 CR3: 0000000427f22000 CR4: 00000000000006e0
> [Wed Feb 27 14:17:09 2019] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [Wed Feb 27 14:17:09 2019] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> ---
>  net/vmw_vsock/virtio_transport_common.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
> index 3ae3a33da70b..502201aaff2a 100644
> --- a/net/vmw_vsock/virtio_transport_common.c
> +++ b/net/vmw_vsock/virtio_transport_common.c
> @@ -662,6 +662,7 @@ static int virtio_transport_reset(struct vsock_sock *vsk,
>   */
>  static int virtio_transport_reset_no_sock(struct virtio_vsock_pkt *pkt)
>  {
> +	const struct virtio_transport *t;
>  	struct virtio_vsock_pkt_info info = {
>  		.op = VIRTIO_VSOCK_OP_RST,
>  		.type = le16_to_cpu(pkt->hdr.type),
> @@ -680,7 +681,11 @@ static int virtio_transport_reset_no_sock(struct virtio_vsock_pkt *pkt)
>  	if (!pkt)
>  		return -ENOMEM;
>  
> -	return virtio_transport_get_ops()->send_pkt(pkt);
> +	t = virtio_transport_get_ops();
> +	if (!t)
> +		return -ENOTCONN;

Should be better to do this check before the virtio_transport_alloc_pkt?

Otherwise, I think we should free that packet before to return -ENOTCONN.

Thanks,
Stefano

> +
> +	return t->send_pkt(pkt);
>  }
>  
>  static void virtio_transport_wait_close(struct sock *sk, long timeout)
> -- 
> 2.21.0
> 

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