From 7e61560628d17ea6b1d8ee370f6d42694cff8758 Mon Sep 17 00:00:00 2001 From: Ulises Mendez Martinez Date: Fri, 4 Sep 2026 15:07:09 +0000 Subject: objtool: Validate disassembler headers in libopcodes probe commit 3f2de814c059 ("objtool: Fix libopcodes linking with static libraries") tested for libopcodes availability by linking a test snippet with a forward declaration of disassemble_init_for_target(). However, testing symbol linkage with an extern declaration only verifies the presence of the library (.so/.a) and bypasses checking for development headers (binutils-dev). On systems where libopcodes is present without development headers installed, the probe succeeds, enabling BUILD_DISAS. Subsequent compilation of objtool then fails: fatal error: 'bfd.h' file not found 113 | #include Additionally, the probe invokes $(HOSTCC) without $(HOSTCFLAGS), ignoring any sysroot or include flags specified for the host compiler. Fix this by including and directly in the test snippet, passing $(HOSTCFLAGS) so host compiler options are respected, and defining PACKAGE="objtool" to satisfy the configuration check in . Fixes: 3f2de814c059 ("objtool: Fix libopcodes linking with static libraries") Fixes: 436326bc525d ("objtool: fix build failure due to missing libopcodes check") Reported-by: Alice Ryhl Assisted-by: Antigravity:Gemini-Next Signed-off-by: Ulises Mendez Martinez Link: https://patch.msgid.link/20260904150710.2997558-1-umendez@google.com Signed-off-by: Josh Poimboeuf --- Documentation/usb/authorization.rst | 129 ++++++++++++++++++++++++++++++++++++ 1 file changed, 129 insertions(+) create mode 100644 Documentation/usb/authorization.rst (limited to 'Documentation/usb/authorization.rst') diff --git a/Documentation/usb/authorization.rst b/Documentation/usb/authorization.rst new file mode 100644 index 000000000..150a14970 --- /dev/null +++ b/Documentation/usb/authorization.rst @@ -0,0 +1,129 @@ +============================================================== +Authorizing (or not) your USB devices to connect to the system +============================================================== + +Copyright (C) 2007 Inaky Perez-Gonzalez Intel Corporation + +This feature allows you to control if a USB device can be used (or +not) in a system. This feature will allow you to implement a lock-down +of USB devices, fully controlled by user space. + +As of now, when a USB device is connected it is configured and +its interfaces are immediately made available to the users. With this +modification, only if root authorizes the device to be configured will +then it be possible to use it. + +Usage +===== + +Authorize a device to connect:: + + $ echo 1 > /sys/bus/usb/devices/DEVICE/authorized + +De-authorize a device:: + + $ echo 0 > /sys/bus/usb/devices/DEVICE/authorized + +Set new devices connected to hostX to be deauthorized by default (ie: +lock down):: + + $ echo 0 > /sys/bus/usb/devices/usbX/authorized_default + +Remove the lock down:: + + $ echo 1 > /sys/bus/usb/devices/usbX/authorized_default + +By default, all USB devices are authorized. Writing "2" to the +authorized_default attribute causes the kernel to authorize by default +only devices connected to internal USB ports. + + +Example system lockdown (lame) +------------------------------ + +Imagine you want to implement a lockdown so only devices of type XYZ +can be connected (for example, it is a kiosk machine with a visible +USB port):: + + boot up + rc.local -> + + for host in /sys/bus/usb/devices/usb* + do + echo 0 > $host/authorized_default + done + +Hookup an script to udev, for new USB devices:: + + if device_is_my_type $DEV + then + echo 1 > $device_path/authorized + done + + +Now, device_is_my_type() is where the juice for a lockdown is. Just +checking if the class, type and protocol match something is the worse +security verification you can make (or the best, for someone willing +to break it). If you need something secure, use crypto and Certificate +Authentication or stuff like that. Something simple for an storage key +could be:: + + function device_is_my_type() + { + echo 1 > authorized # temporarily authorize it + # FIXME: make sure none can mount it + mount DEVICENODE /mntpoint + sum=$(md5sum /mntpoint/.signature) + if [ $sum = $(cat /etc/lockdown/keysum) ] + then + echo "We are good, connected" + umount /mntpoint + # Other stuff so others can use it + else + echo 0 > authorized + fi + } + + +Of course, this is lame, you'd want to do a real certificate +verification stuff with PKI, so you don't depend on a shared secret, +etc, but you get the idea. Anybody with access to a device gadget kit +can fake descriptors and device info. Don't trust that. You are +welcome. + + +Interface authorization +----------------------- + +There is a similar approach to allow or deny specific USB interfaces. +That allows to block only a subset of an USB device. + +Authorize an interface:: + + $ echo 1 > /sys/bus/usb/devices/INTERFACE/authorized + +Deauthorize an interface:: + + $ echo 0 > /sys/bus/usb/devices/INTERFACE/authorized + +The default value for new interfaces +on a particular USB bus can be changed, too. + +Allow interfaces per default:: + + $ echo 1 > /sys/bus/usb/devices/usbX/interface_authorized_default + +Deny interfaces per default:: + + $ echo 0 > /sys/bus/usb/devices/usbX/interface_authorized_default + +Per default the interface_authorized_default bit is 1. +So all interfaces would authorized per default. + +Note: + If a deauthorized interface will be authorized so the driver probing must + be triggered manually by writing INTERFACE to /sys/bus/usb/drivers_probe + +For drivers that need multiple interfaces all needed interfaces should be +authorized first. After that the drivers should be probed. +This avoids side effects. -- cgit v1.3.1