Hello all, Just wondering, if one is already using selinux in enforcing mode, does systemd hardening provide any additional benefit?
Daniel On 16.01.18 12:21, Ludovic Gasc wrote: > Hi, > > I have merged config files from Tony, Robert, and me. > I have tried to be the most generic, the result below. > > It seems to work here without regression, except a warning: > managed-keys-zone: Unable to fetch DNSKEY set '.': operation canceled > > But only at the first boot, I don't see the message anymore when I > restart the daemon. > Any clue ? > > Thanks for your feedbacks. > > [Unit] > After=network-online.target > > [Service] > Type=simple > TimeoutSec=25 > Restart=always > RestartSec=1 > User=bind > Group=bind > CapabilityBoundingSet=CAP_NET_BIND_SERVICE > AmbientCapabilities=CAP_NET_BIND_SERVICE > SystemCallFilter=~@mount @debug acct modify_ldt add_key adjtimex > clock_adjtime delete_module fanotify_init finit_module get_mempolicy > init_module io_destroy io_getevents iopl ioperm io_setup io_submit > io_cancel kcmp kexec_load keyctl lookup_dcookie migrate_pages move_pages > open_by_handle_at perf_event_open process_vm_readv process_vm_writev > ptrace remap_file_pages request_key set_mempolicy swapoff swapon uselib > vmsplice > > NoNewPrivileges=true > PrivateDevices=true > PrivateTmp=true > ProtectHome=true > ProtectSystem=strict > ProtectKernelModules=true > ProtectKernelTunables=true > ProtectControlGroups=true > InaccessiblePaths=/home > InaccessiblePaths=/opt > InaccessiblePaths=/root > ReadWritePaths=/run/named > ReadWritePaths=/var/cache/bind > ReadWritePaths=/var/lib/bind > > > -- > Ludovic Gasc (GMLudo) > > 2018-01-15 21:14 GMT+01:00 Robert Edmonds <edmo...@mycre.ws > <mailto:edmo...@mycre.ws>>: > > Tony Finch wrote: > > Ludovic Gasc <gml...@gmail.com <mailto:gml...@gmail.com>> wrote: > > > > > > 1. The list of minimal capabilities needed for bind to run correctly: > > > http://man7.org/linux/man-pages/man7/capabilities.7.html > <http://man7.org/linux/man-pages/man7/capabilities.7.html> > > > > named already drops capabilities - have a look at the code around here: > > > https://source.isc.org/cgi-bin/gitweb.cgi?p=bind9.git;a=blob;f=bin/named/unix/os.c;hb=v9_11_2#l234 > > <https://source.isc.org/cgi-bin/gitweb.cgi?p=bind9.git;a=blob;f=bin/named/unix/os.c;hb=v9_11_2#l234> > > > > Note that it's a bit clever - the privileges are dropped in two stages, > > right at the start, and after the server has been configured. > > I checked just now to see what that code actually ends up doing, and on > my system I ended up with: > > $ grep -h ^Cap /proc/$(pidof named)/**/status | sort | uniq -c > 6 CapAmb: 0000000000000000 > 6 CapBnd: 0000003fffffffff > 6 CapEff: 0000000001000400 > 6 CapInh: 0000000000000000 > 6 CapPrm: 0000000001000400 > $ > > That decodes to: > > - The effective and permitted capabilities sets were reduced to > CAP_NET_BIND_SERVICE and CAP_SYS_RESOURCE. > > - The ambient and inheritable capabilities sets were cleared. > > - The capability bounding set was left completely open-ended. > > It's not clear why CAP_SYS_RESOURCE needs to be retained past startup: > > /* > * XXX We might want to add CAP_SYS_RESOURCE, though it's not > * clear it would work right given the way linuxthreads > work. > * XXXDCL But since we need to be able to set the maximum number > * of files, the stack size, data size, and core dump size to > * support named.conf options, this is now being added to test. > */ > SET_CAP(CAP_SYS_RESOURCE); > > See commits 5e4b7294d88ab58371d8c98e05ea80086dcb67cd, > 108490a7f8529aff50a0ac7897580b59a73d9845. "[T]o test"? > > CAP_SYS_RESOURCE is documented as permitting: > > CAP_SYS_RESOURCE > * Use reserved space on ext2 filesystems; > * make ioctl(2) calls controlling ext3 journaling; > * override disk quota limits; > * increase resource limits (see setrlimit(2)); > * override RLIMIT_NPROC resource limit; > * override maximum number of consoles on console allocation; > * override maximum number of keymaps; > * allow more than 64hz interrupts from the real-time clock; > * raise msg_qbytes limit for a System V message queue > above the > limit in /proc/sys/kernel/msgmnb (see msgop(2) and > msgctl(2)); > * allow the RLIMIT_NOFILE resource limit on the number > of "in- > flight" file descriptors to be bypassed when > passing file > descriptors to another process via a UNIX domain > socket (see > unix(7)); > * override the /proc/sys/fs/pipe-size-max limit when > setting the > capacity of a pipe using the F_SETPIPE_SZ fcntl(2) command. > * use F_SETPIPE_SZ to increase the capacity of a pipe > above the > limit specified by /proc/sys/fs/pipe-max-size; > * override /proc/sys/fs/mqueue/queues_max limit when > creating > POSIX message queues (see mq_overview(7)); > * employ the prctl(2) PR_SET_MM operation; > * set /proc/[pid]/oom_score_adj to a value lower than the > value > last set by a process with CAP_SYS_RESOURCE. > > I would guess that retaining CAP_NET_BIND_SERVICE and CAP_SYS_RESOURCE > during the process runtime permits open-ended reloading of the config at > runtime (e.g., binding to a new IP address on port 53 without needing to > restart the daemon). So even though BIND drops some capabilities, it's > still running with elevated privileges compared to a traditional > non-root user. > > systemd permits a nice pattern for network daemons that want to run as > an unprivileged user, but bind to a privileged port (and without using > socket activation), without starting the process as root. Basically, you > put something like this in the unit file: > > [Service] > User=… > Group=… > CapabilityBoundingSet=CAP_NET_BIND_SERVICE CAP_SYS_CHROOT > CAP_SETPCAP > AmbientCapabilities=CAP_NET_BIND_SERVICE CAP_SYS_CHROOT CAP_SETPCAP > … > > Any needed filesystem directories and permissions need to be set up > correctly before hand. The service is started by the init system as the > unprivileged User/Group specified in the unit file, so there's no need > to change UID/GID. CAP_NET_BIND_SERVICE is then used to bind to a > privileged port, CAP_SYS_CHROOT is used to perform the chroot, and > CAP_SETPCAP is used to drop all remaining capabilities from the > capability sets and the capability bounding set, so you end up with a > completely unprivileged process at runtime. (Alternatively you could > keep CAP_NET_BIND_SERVICE and drop CAP_SYS_CHROOT and CAP_SETPCAP, if > you wanted to retain the capability to perform privileged binds at > runtime. Or you could eliminate CAP_SYS_CHROOT and use other systemd > functionality to make parts of the filesystem inaccessible, etc.) This > pattern might be a bit hard to retrofit into BIND at this point, though, > other than by adding more knobs. > > -- > Robert Edmonds > _______________________________________________ > Please visit https://lists.isc.org/mailman/listinfo/bind-users > <https://lists.isc.org/mailman/listinfo/bind-users> to unsubscribe > from this list > > bind-users mailing list > bind-users@lists.isc.org <mailto:bind-users@lists.isc.org> > https://lists.isc.org/mailman/listinfo/bind-users > <https://lists.isc.org/mailman/listinfo/bind-users> > _______________________________________________ Please visit https://lists.isc.org/mailman/listinfo/bind-users to unsubscribe from this list bind-users mailing list bind-users@lists.isc.org https://lists.isc.org/mailman/listinfo/bind-users
