linux-kernel - Re: [PATCH] usbip: fix vhci races in connection tear down

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Date:   Fri, 12 Mar 2021 11:45:04 +0100
From:   Johan Hovold <johan@...nel.org>
To:     Shuah Khan <skhan@...uxfoundation.org>
Cc:     valentina.manea.m@...il.com, shuah@...nel.org,
        gregkh@...uxfoundation.org, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        syzbot+a93fba6d384346a761e3@...kaller.appspotmail.com
Subject: Re: [PATCH] usbip: fix vhci races in connection tear down

On Thu, Mar 11, 2021 at 07:27:37PM -0700, Shuah Khan wrote:
> vhci_shutdown_connection() references connection state (tcp_socket,
> tcp_rx, tcp_tx, sockfd) saved in usbpip_device without holding the
> lock.
> 
> Current connection tear down sequence:
> Step 1: shutdown the socket
> Step 2: stop rx thread and reset tcp_rx pointer
> Step 3: stop tx thread and reset tcp_tx pointer
> Step 4: Reset tcp_socket and sockfd
> 
> There are several race windows between these steps. In addition, device
> reset routine (vhci_device_reset) resets tcp_socket and sockfd holding
> the lock.
> 
> Fix these races:
> - Introduce in_disconnect flag to ensure vhci_shutdown_connection() runs
>   only once.
> - Change attach_store() to initialize in_disconnect to false while
>   initializing connection status (tcp_socket, tcp_rx, tcp_tx, sockfd)
> - Change vhci_shutdown_connection() to check in_disconnect and bail
>   out if disconnect is in progress.
> - Change vhci_shutdown_connection() to
>   -- hold lock to save connection state pointers and unlock.
>   -- Shutdown the socket and stop threads.
>   -- Hold lock to clear connection status and in_disconnect flag.
> - Change vhci_device_reset() to reset tcp_socket and sockfd.
>   if !in_disconnect
> 
> Tested syzbot and the reproducer did not trigger any issue.
> 
> Reported-and-tested-by: syzbot+a93fba6d384346a761e3@...kaller.appspotmail.com
> Signed-off-by: Shuah Khan <skhan@...uxfoundation.org>
> ---
>  drivers/usb/usbip/usbip_common.h |  1 +
>  drivers/usb/usbip/vhci_hcd.c     | 55 +++++++++++++++++++++++---------
>  drivers/usb/usbip/vhci_sysfs.c   |  4 +++
>  3 files changed, 45 insertions(+), 15 deletions(-)

> diff --git a/drivers/usb/usbip/vhci_hcd.c b/drivers/usb/usbip/vhci_hcd.c
> index 3209b5ddd30c..c1917efe5737 100644
> --- a/drivers/usb/usbip/vhci_hcd.c
> +++ b/drivers/usb/usbip/vhci_hcd.c
> @@ -1007,31 +1007,54 @@ static void vhci_device_unlink_cleanup(struct vhci_device *vdev)
>  static void vhci_shutdown_connection(struct usbip_device *ud)
>  {
>  	struct vhci_device *vdev = container_of(ud, struct vhci_device, ud);
> +	unsigned long flags;
> +	struct socket *socket;
> +	struct task_struct *tcp_rx = NULL;
> +	struct task_struct *tcp_tx = NULL;
> +	int sockfd = 0;
> +
> +	spin_lock_irqsave(&ud->lock, flags);
> +	if (vdev->ud.in_disconnect) {
> +		pr_info("%s: Disconnect in progress for sockfd %d\n",
> +			__func__, ud->sockfd);

Looks like you forgot to remove all you debug printks like this one
before submitting.

> +		spin_unlock_irqrestore(&ud->lock, flags);
> +		return;
> +	}

Johan