attach_store() is invoked when user requests import (attach) a device from usbip host.

Attach and detach are governed by local state and shared state - Shared state (usbip device status) - Device status is used to manage the attach and detach operations on import-able devices. - Local state (tcp_socket, rx and tx thread task_struct ptrs) A valid tcp_socket controls rx and tx thread operations while the device is in exported state. - Device has to be in the right state to be attached and detached.

Attach sequence includes validating the socket and creating receive (rx) and transmit (tx) threads to talk to the host to get access to the imported device. rx and tx threads depends on local and shared state to be correct and in sync.

Detach sequence shuts the socket down and stops the rx and tx threads. Detach sequence relies on local and shared states to be in sync.

There are races in updating the local and shared status in the current attach sequence resulting in crashes. These stem from starting rx and tx threads before local and global state is updated correctly to be in sync.

1. Doesn't handle kthread_create() error and saves invalid ptr in local state that drives rx and tx threads. 2. Updates tcp_socket and sockfd, starts stub_rx and stub_tx threads before updating usbip_device status to VDEV_ST_NOTASSIGNED. This opens up a race condition between the threads, port connect, and detach handling.

Fix the above problems: - Stop using kthread_get_run() macro to create/start threads. - Create threads and get task struct reference. - Add kthread_create() failure handling and bail out. - Hold vhci and usbip_device locks to update local and shared states after creating rx and tx threads. - Update usbip_device status to VDEV_ST_NOTASSIGNED. - Update usbip_device tcp_socket, sockfd, tcp_rx, and tcp_tx - Start threads after usbip_device (tcp_socket, sockfd, tcp_rx, tcp_tx, and status) is complete.

Credit goes to syzbot and Tetsuo Handa for finding and root-causing the kthread_get_run() improper error handling problem and others. This is hard problem to find and debug since the races aren't seen in a normal case. Fuzzing forces the race window to be small enough for the kthread_get_run() error path bug and starting threads before updating the local and shared state bug in the attach sequence. - Update usbip_device tcp_rx and tcp_tx pointers holding vhci and usbip_device locks.

Tested with syzbot reproducer: - https://syzkaller.appspot.com/text?tag=ReproC&x=14801034d00000

Reported-by: syzbot syzbot+a93fba6d384346a761e3@syzkaller.appspotmail.com Reported-by: syzbot syzbot+bf1a360e305ee719e364@syzkaller.appspotmail.com Reported-by: syzbot syzbot+95ce4b142579611ef0a9@syzkaller.appspotmail.com Reported-by: Tetsuo Handa penguin-kernel@I-love.SAKURA.ne.jp Fixes: 9720b4bc76a83807 ("staging/usbip: convert to kthread") Cc: stable@vger.kernel.org Signed-off-by: Shuah Khan skhan@linuxfoundation.org --- drivers/usb/usbip/vhci_sysfs.c | 29 +++++++++++++++++++++++++---- 1 file changed, 25 insertions(+), 4 deletions(-)

diff --git a/drivers/usb/usbip/vhci_sysfs.c b/drivers/usb/usbip/vhci_sysfs.c index 1e1ae9bd06ab..c4b4256e5dad 100644 --- a/drivers/usb/usbip/vhci_sysfs.c +++ b/drivers/usb/usbip/vhci_sysfs.c @@ -312,6 +312,8 @@ static ssize_t attach_store(struct device *dev, struct device_attribute *attr, struct vhci *vhci; int err; unsigned long flags; + struct task_struct *tcp_rx = NULL; + struct task_struct *tcp_tx = NULL;

/* * @rhport: port number of vhci_hcd @@ -360,9 +362,24 @@ static ssize_t attach_store(struct device *dev, struct device_attribute *attr, return -EINVAL; }

- /* now need lock until setting vdev status as used */ + /* create threads before locking */ + tcp_rx = kthread_create(vhci_rx_loop, &vdev->ud, "vhci_rx"); + if (IS_ERR(tcp_rx)) { + sockfd_put(socket); + return -EINVAL; + } + tcp_tx = kthread_create(vhci_tx_loop, &vdev->ud, "vhci_tx"); + if (IS_ERR(tcp_tx)) { + kthread_stop(tcp_rx); + sockfd_put(socket); + return -EINVAL; + } + + /* get task structs now */ + get_task_struct(tcp_rx); + get_task_struct(tcp_tx);

- /* begin a lock */ + /* now begin lock until setting vdev status set */ spin_lock_irqsave(&vhci->lock, flags); spin_lock(&vdev->ud.lock);

@@ -372,6 +389,8 @@ static ssize_t attach_store(struct device *dev, struct device_attribute *attr, spin_unlock_irqrestore(&vhci->lock, flags);

sockfd_put(socket); + kthread_stop_put(tcp_rx); + kthread_stop_put(tcp_tx);

dev_err(dev, "port %d already used\n", rhport); /* @@ -390,6 +409,8 @@ static ssize_t attach_store(struct device *dev, struct device_attribute *attr, vdev->speed = speed; vdev->ud.sockfd = sockfd; vdev->ud.tcp_socket = socket; + vdev->ud.tcp_rx = tcp_rx; + vdev->ud.tcp_tx = tcp_tx; vdev->ud.status = VDEV_ST_NOTASSIGNED; usbip_kcov_handle_init(&vdev->ud);

@@ -397,8 +418,8 @@ static ssize_t attach_store(struct device *dev, struct device_attribute *attr, spin_unlock_irqrestore(&vhci->lock, flags); /* end the lock */

- vdev->ud.tcp_rx = kthread_get_run(vhci_rx_loop, &vdev->ud, "vhci_rx"); - vdev->ud.tcp_tx = kthread_get_run(vhci_tx_loop, &vdev->ud, "vhci_tx"); + wake_up_process(vdev->ud.tcp_rx); + wake_up_process(vdev->ud.tcp_tx);

rh_port_connect(vdev, speed);