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authorAlan Stern <stern@rowland.harvard.edu>2012-09-26 13:09:53 -0400
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2012-10-02 09:47:55 -0700
commitb15ab4ac6ae748d3552b0cb112dff5c9c567d4ca (patch)
parent8ef8fa7479fff9313387b873413f5ae233a2bd04 (diff)
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 <stern@rowland.harvard.edu> Reported-by: Don Zickus <dzickus@redhat.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2 files changed, 3 insertions, 5 deletions
diff --git a/drivers/usb/core/devices.c b/drivers/usb/core/devices.c
index 0149c0976e9c..ca98341a21b9 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)
ret = usb_device_dump(&buf, &nbytes, &skip_bytes, ppos,
diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
index 45e090850c93..9d5af9bb990c 100644
--- a/drivers/usb/core/hcd.c
+++ b/drivers/usb/core/hcd.c
@@ -977,10 +977,7 @@ 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);
@@ -989,6 +986,7 @@ 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;