Linux kernel: CVE-2017-6074: DCCP double-free vulnerability (local root)
This is a good reason for systems running untrusted code to disable module automatic loading. Almost nobody uses DCCP, and as a result, almost nobody <i>looks at</i> the DCCP code, writes bad userspace apps that trigger kernel bugs that get debugged, etc. We rarely see double-frees in the TCP or UDP implementations.<p>On my Debian kernel, CONFIG_IP_DCCP is set to "m" (in /boot/config-`uname -r`), which means that DCCP support is built as a module. The code isn't loaded until the first program tries to call socket(...IPPROTO_DCCP). At that point, the kernel will look at /proc/sys/kernel/modprobe and run that program, /sbin/modprobe by default, to load dccp.ko.<p>Automatic module loading is great when e.g. udev runs and detects what hardware you have, but it's probably not something you'd ever need once a system has completed boot. A very simple hardening measure for machines running untrusted unprivileged code is to echo /bin/false > /proc/sys/kernel/modprobe, late in the boot process (e.g., in /etc/rc.local).<p>The downside is that system administrator won't be able to run tools that require loading modules, of which iptables is probably the most notable one. A better option than /bin/false is a shell script that logs its arguments to syslog, e.g., `logger -p authpriv.info -- "Refused modprobe $*"`. The sysadmin can manually run modprobe on whatever module name got syslogged (or temporarily set /proc/sys/kernel/modprobe back to /sbin/modprobe). And you can alert on that syslog line to see if there's an attack in progress.<p>(Does anyone know if it's possible to disable module auto-loading for a tree/namespace of processes, e.g. a Docker container, but keep it working for the base system?)