RFE Device Auditing

Feature Description

The problem is that devices can be added or removed from a system and the audit subsystem may have no context or ability to know which device and its details for further auditing tasks.

Feature Design

The kernel recognises devices being added and removed via the device_add ( drivers/base/core.c ) function which delegates work to the relevant driver through a notifier callback chain.

device_add()
   if (dev->bus)
            blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
                                         BUS_NOTIFY_ADD_DEVICE, dev);
device_del()
    if (dev->bus)
            blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
                                         BUS_NOTIFY_DEL_DEVICE, dev);

At the moment, some bus already have their own notification chain. USB is prime example that already has an add example using usb_register_notify()

Hooking into this notifier chain and introspecting the dev nodes and push the data into the audit subsystem. Some subsystems have existing blocking notifier call chains, these may need to be used instead.

Development Tasks

1. Build out of tree kernel module for testing.

   • This was not possible due to some symbols not being exported for out of tree ( audit_log_untrustedstring )
   • This needs to be done -in- tree either as its own file or part of each subsystem.

2. Build this as part of the existing systems that use their own registrations systems.

Functional Testing and Verification

USB Devices being plugged in generate an audit device with strings escaped.

Example Audit Records

Decoded:

$ ausearch -ts today |grep AUDIT_DEVICE
type=AUDIT_DEVICE msg=audit(1458748898.855:1414): action=add manufacturer="SanDisk" product=53616E4469736B204372757A6572 serial="4861121412120504" major=189 minor=2 bus=usb

Encoded:

$ ausearch -ts today -i |grep AUDIT_DEVICE
type=AUDIT_DEVICE msg=audit(24/03/16 03:01:38.855:1414) : action=add manufacturer=SanDisk product=SanDisk Cruzer serial=4861121412120504 major=189 minor=2 bus=usb

Fields:

• action: [add|remove] The action that the kernel is taking to the device.
• manufacturer : A String provided by the device, may be omitted if blank or not provided or unknown.
• product: A String value of the provided USB device, may be omitted if blank or not provided or unknown.
• serial: A String value may include any valid ascii character, may be omitted if blank or not provided or unknown.
• major: A numeric value of the the major number of the device being added.
• minor: A numeric value of the minor number of the device being added.

Current status:

• Patch has been submitted to upstream linux-usb and audit mailing lists
• Patch comments: ** Make it more generic ** Fine if its 'Just for being eyeballed' for admins.

Next steps:

• Hook into the generic bus/add notifier iterating through the kobj bus list.
• Create a table for other device types that can hook into the same exported fields.

Bugzilla and Issue Trackers

GH/audit-kernel #1

RHBZ #1210949