Linux 4.15 Released

02 Feb 2018 tags: audit selinux

Linux v4.15 was released on Sunday, January 28th; this is a quick summary of the SELinux and audit changes.

SELinux

• A new SELinux object class was added, “bpf”, to control access to the extended Berkeley Packet Filter (eBPF) virtual machine in the Linux Kernel, which can be accessed via the bpf(2) system call. The new object class is defined with the following permissions:

  bpf { map_create map_read map_write prog_load prog_run }
  

  The “map_create” permission controls the ability to create new eBPF maps, where the “map_read” and “map_write” permissions control read and write access to eBPF maps. The “prog_load” permission controls the ability to load an eBPF program into the kernel and the “prog_run” permission controls the ability execute a previously loaded eBPF program. Like most system resources, eBPF maps and programs inherit their labels from the originating SELinux domain.

• The file extended attribute permission code was changed to use the common capability code for any non-SELinux extended attributes. This fixed a problem with file capabilities in user namespaces.

• Converted the SELinux internal hash table implementation to use kmem_cache, reducing runtime memory consumption by a small amount.

• Various small code cleanups to remove build warnings and unneeded variable assignments.

Audit

• Due to a large number of PATH records created by tracefs and debugfs, a new mechanism was introduced which allows the filtering of PATH records based on the filesystem type. Richard Guy Briggs provides a good explanation of this new feature in the patch’s description:

  From: Richard Guy Briggs

  audit: filter PATH records keyed on filesystem magic

  Tracefs or debugfs were causing hundreds to thousands of PATH records to be associated with the init_module and finit_module SYSCALL records on a few modules when the following rule was in place for startup:
    -a always,exit -F arch=x86_64 -S init_module -F key=mod-load

  Provide a method to ignore these large number of PATH records from overwhelming the logs if they are not of interest. Introduce a new filter list “AUDIT_FILTER_FS”, with a new field type AUDIT_FSTYPE, which keys off the filesystem 4-octet hexadecimal magic identifier to filter specific filesystem PATH records.

  An example rule would look like:
    -a never,filesystem -F fstype=0x74726163 -F key=ignore_tracefs
    -a never,filesystem -F fstype=0x64626720 -F key=ignore_debugfs

  Arguably the better way to address this issue is to disable tracefs and debugfs on boot from production systems.

• Fixed a bug where the kernel was not initializing the audit subsystem early enough at boot and was missing audit records generated by PID 1 (init/systemd/etc.). In addition to fixing this particular bug there were a number of small code cleanups and general improvements to the audit initialization code.

• Fixed a bug where the kernel did not recognize when the audit daemon was attempting to shut down the kernel/auditd connection by sending an AUDIT_SET message with a PID 0 value.

• The audit file and directory write syscall filters were updated with additional syscalls.

• An old and unused function, audit_log_secctx(), was removed.

UPDATE: Added mention of the SELinux “bpf” object class that was added in Linux v4.15.