Hello,
With recent Ubuntu 18/Linux Mint 19.2 etc, lots of user space programs
(in particular systemd/eudev/upowerd) have problems with the "BIND/UNBIND"
events produced since kernel 4.13.
Some problems are described, when googling for
linux "usb" "bind event"
Now this might be blamed on these particular user space programs.
But: This also means that programs accessing a USB device via the generic
usbfs layer can easily flood the kernel and all user space programs listening
to uevents with tons of BIND/UNBIND events by calling
ioctl(usbfd, USBDEVFS_CLAIMINTERFACE, &intf);
ioctl(usbfd, USBDEVFS_RELEASEINTERFACE, &intf);
in a tight loop.
Of course this is an extreme example, but I have a use case where exactly
this happens (running Linux Mint 19.2).
The result is that "systemd-udev" needs > 100% CPU and
upowerd spams the system log with messages about "bind/unbind" events.
I am also not sure if these particular bind/unbind events contain any useful
information; these events just mean an arbitrary user space program has
bound/unbound from a particular USB interface.
The following patch tries to suppress emission of uevents
for USB interfaces which are claimed/released via usbfs.
I am not sure if this is the right way to do it, but at least
it seems to do what I intended...
with best regards
Ingo Rohloff
From 57970b0a5a36809ddb8f15687c18ca2147dc73bd Mon Sep 17 00:00:00 2001
From: Ingo Rohloff <ingo.rohloff@xxxxxxxxxxxxxx>
Date: Tue, 8 Oct 2019 20:27:57 +0200
Subject: [PATCH] USB: usbfs: Suppress emission of uevents for interfaces
handled via usbfs.
commit 1455cf8dbfd0
("driver core: emit uevents when device is bound to a driver")
added BIND and UNBIND events when a driver is bound/unbound
to a physical device.
For USB devices which are handled via the generic usbfs layer
(via libusb for example). This is problematic:
Each time a user space program calls
ioctl(usb_fd, USBDEVFS_CLAIMINTERFACE, &usb_intf_nr);
and then later
ioctl(usb_fd, USBDEVFS_RELEASEINTERFACE, &usb_intf_nr);
The kernel will now produce a BIND/UNBIND event, which
does not really contain any useful information.
Additionally this easily allows a user space program to run a
DoS attack against programs which listen to uevents
(in particular systemd/eudev/upowerd):
A malicious user space program just has to call in a tight loop
ioctl(usbfd, USBDEVFS_CLAIMINTERFACE, &intf);
ioctl(usbfd, USBDEVFS_RELEASEINTERFACE, &intf);
with this loop the malicious user space program floods
the kernel and all programs listening to uevents with
tons of BIND/UNBIND events.
The following patch tries to suppress uevents for interfaces
claimed via usbfs.
---
drivers/usb/core/devio.c | 7 ++++++-
drivers/usb/core/driver.c | 2 ++
2 files changed, 8 insertions(+), 1 deletion(-)
diff --git a/drivers/usb/core/devio.c b/drivers/usb/core/devio.c
index 3f899552f6e3..a1af1d9b2ae7 100644
--- a/drivers/usb/core/devio.c
+++ b/drivers/usb/core/devio.c
@@ -764,8 +764,13 @@ static int claimintf(struct usb_dev_state *ps, unsigned int ifnum)
intf = usb_ifnum_to_if(dev, ifnum);
if (!intf)
err = -ENOENT;
- else
+ else {
+ /* suppress uevents for devices handled by usbfs */
+ dev_set_uevent_suppress(&intf->dev, 1);
err = usb_driver_claim_interface(&usbfs_driver, intf, ps);
+ if (err != 0)
+ dev_set_uevent_suppress(&intf->dev, 0);
+ }
if (err == 0)
set_bit(ifnum, &ps->ifclaimed);
return err;
diff --git a/drivers/usb/core/driver.c b/drivers/usb/core/driver.c
index 2b27d232d7a7..6a15bc5c2869 100644
--- a/drivers/usb/core/driver.c
+++ b/drivers/usb/core/driver.c
@@ -594,6 +594,8 @@ void usb_driver_release_interface(struct usb_driver *driver,
*/
if (device_is_registered(dev)) {
device_release_driver(dev);
+ /* make sure we allow uevents again */
+ dev_set_uevent_suppress(dev, 0);
} else {
device_lock(dev);
usb_unbind_interface(dev);
--
2.17.1
