From 0ecf1c24aec118ccbc0c67f2fd61a1313b56f322 Mon Sep 17 00:00:00 2001 From: Alan Stern Date: Wed, 26 Sep 2012 13:09:53 -0400 Subject: [PATCH] USB: Fix race condition when removing host controllers commit 0d00dc2611abbe6ad244d50569c2ee82ce42846c upstream. This patch (as1607) fixes a race that can occur if a USB host controller is removed while a process is reading the /sys/kernel/debug/usb/devices file. The usb_device_read() routine uses the bus->root_hub pointer to determine whether or not the root hub is registered. The is not a valid test, because the pointer is set before the root hub gets registered and remains set even after the root hub is unregistered and deallocated. As a result, usb_device_read() or usb_device_dump() can access freed memory, causing an oops. The patch changes the test to use the hcd->rh_registered flag, which does get set and cleared at the appropriate times. It also makes sure to hold the usb_bus_list_lock mutex while setting the flag, so that usb_device_read() will become aware of new root hubs as soon as they are registered. Signed-off-by: Alan Stern Reported-by: Don Zickus Signed-off-by: Greg Kroah-Hartman Signed-off-by: Ben Hutchings --- drivers/usb/core/devices.c | 2 +- drivers/usb/core/hcd.c | 6 ++---- 2 files changed, 3 insertions(+), 5 deletions(-) diff --git a/drivers/usb/core/devices.c b/drivers/usb/core/devices.c index d95696584762..3440812b4a84 100644 --- a/drivers/usb/core/devices.c +++ b/drivers/usb/core/devices.c @@ -624,7 +624,7 @@ static ssize_t usb_device_read(struct file *file, char __user *buf, /* print devices for all busses */ list_for_each_entry(bus, &usb_bus_list, bus_list) { /* recurse through all children of the root hub */ - if (!bus->root_hub) + if (!bus_to_hcd(bus)->rh_registered) continue; usb_lock_device(bus->root_hub); ret = usb_device_dump(&buf, &nbytes, &skip_bytes, ppos, diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c index 8cb9304e8d4f..032e5a6e0bfc 100644 --- a/drivers/usb/core/hcd.c +++ b/drivers/usb/core/hcd.c @@ -1002,10 +1002,7 @@ static int register_root_hub(struct usb_hcd *hcd) if (retval) { dev_err (parent_dev, "can't register root hub for %s, %d\n", dev_name(&usb_dev->dev), retval); - } - mutex_unlock(&usb_bus_list_lock); - - if (retval == 0) { + } else { spin_lock_irq (&hcd_root_hub_lock); hcd->rh_registered = 1; spin_unlock_irq (&hcd_root_hub_lock); @@ -1014,6 +1011,7 @@ static int register_root_hub(struct usb_hcd *hcd) if (HCD_DEAD(hcd)) usb_hc_died (hcd); /* This time clean up */ } + mutex_unlock(&usb_bus_list_lock); return retval; } -- 2.39.2