3.16.78-rc1 review patch. If anyone has any objections, please let me know.
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From: Alan Stern stern@rowland.harvard.edu
commit 303911cfc5b95d33687d9046133ff184cf5043ff upstream.
The syzbot fuzzer has found two (!) races in the USB character device registration and deregistration routines. This patch fixes the races.
The first race results from the fact that usb_deregister_dev() sets usb_minors[intf->minor] to NULL before calling device_destroy() on the class device. This leaves a window during which another thread can allocate the same minor number but will encounter a duplicate name error when it tries to register its own class device. A typical error message in the system log would look like:
sysfs: cannot create duplicate filename '/class/usbmisc/ldusb0'
The patch fixes this race by destroying the class device first.
The second race is in usb_register_dev(). When that routine runs, it first allocates a minor number, then drops minor_rwsem, and then creates the class device. If the device creation fails, the minor number is deallocated and the whole routine returns an error. But during the time while minor_rwsem was dropped, there is a window in which the minor number is allocated and so another thread can successfully open the device file. Typically this results in use-after-free errors or invalid accesses when the other thread closes its open file reference, because the kernel then tries to release resources that were already deallocated when usb_register_dev() failed. The patch fixes this race by keeping minor_rwsem locked throughout the entire routine.
Reported-and-tested-by: syzbot+30cf45ebfe0b0c4847a1@syzkaller.appspotmail.com Signed-off-by: Alan Stern stern@rowland.harvard.edu Link: https://lore.kernel.org/r/Pine.LNX.4.44L0.1908121607590.1659-100000@iolanthe... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Ben Hutchings ben@decadent.org.uk --- drivers/usb/core/file.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-)
--- a/drivers/usb/core/file.c +++ b/drivers/usb/core/file.c @@ -191,9 +191,10 @@ int usb_register_dev(struct usb_interfac intf->minor = minor; break; } - up_write(&minor_rwsem); - if (intf->minor < 0) + if (intf->minor < 0) { + up_write(&minor_rwsem); return -EXFULL; + }
/* create a usb class device for this usb interface */ snprintf(name, sizeof(name), class_driver->name, minor - minor_base); @@ -206,12 +207,11 @@ int usb_register_dev(struct usb_interfac MKDEV(USB_MAJOR, minor), class_driver, "%s", temp); if (IS_ERR(intf->usb_dev)) { - down_write(&minor_rwsem); usb_minors[minor] = NULL; intf->minor = -1; - up_write(&minor_rwsem); retval = PTR_ERR(intf->usb_dev); } + up_write(&minor_rwsem); return retval; } EXPORT_SYMBOL_GPL(usb_register_dev); @@ -237,12 +237,12 @@ void usb_deregister_dev(struct usb_inter return;
dev_dbg(&intf->dev, "removing %d minor\n", intf->minor); + device_destroy(usb_class->class, MKDEV(USB_MAJOR, intf->minor));
down_write(&minor_rwsem); usb_minors[intf->minor] = NULL; up_write(&minor_rwsem);
- device_destroy(usb_class->class, MKDEV(USB_MAJOR, intf->minor)); intf->usb_dev = NULL; intf->minor = -1; destroy_usb_class();