This is a note to let you know that I've just added the patch titled
USB: core: Fix races in character device registration and
to my usb git tree which can be found at git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git in the usb-linus branch.
The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)
The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.
If you have any questions about this process, please let me know.
From 303911cfc5b95d33687d9046133ff184cf5043ff Mon Sep 17 00:00:00 2001
From: Alan Stern stern@rowland.harvard.edu Date: Mon, 12 Aug 2019 16:11:07 -0400 Subject: USB: core: Fix races in character device registration and deregistraion
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 CC: stable@vger.kernel.org Link: https://lore.kernel.org/r/Pine.LNX.4.44L0.1908121607590.1659-100000@iolanthe... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/usb/core/file.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-)
diff --git a/drivers/usb/core/file.c b/drivers/usb/core/file.c index 65de6f73b672..558890ada0e5 100644 --- a/drivers/usb/core/file.c +++ b/drivers/usb/core/file.c @@ -193,9 +193,10 @@ int usb_register_dev(struct usb_interface *intf, 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); @@ -203,12 +204,11 @@ int usb_register_dev(struct usb_interface *intf, MKDEV(USB_MAJOR, minor), class_driver, "%s", kbasename(name)); 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); @@ -234,12 +234,12 @@ void usb_deregister_dev(struct usb_interface *intf, 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();