Landlock LSM: Towards unprivileged sandboxing @ All Systems Go! 2017

Transcript

1. Landlock LSM Towards unprivileged sandboxing michael@kinvolk.io
2. Proposed new LSM by Mickaël Salaün First RFC March 2016, Today in iteration v7 "seccomp-object: From attack surface reduction to sandboxing"
3. Goal "empower any process, including unprivileged ones, to securely restrict themselves" Note: current version (Landlock patch v7) requires CAP_SYS_ADMIN
4. Patchset v7 a minimum viable product a stackable LSM using eBPF (new pogram type BPF_PROG_TYPE_LANDLOCK_RULE) focused on filesystem access control source: https://landlock.io/talks/2017-09-14_landlock-lss.pdf
5. Why eBPF very limited kernel attack surface strict rules for policies (enforced through eBPF verifier)
6. Demo ./landlock landlock1_kern.o /usr/bin/bash
7. Events Landlock groups 33 filesystem-related LSM hooks into LANDLOCK_SUBTYPE_EVENT_FS an event "describes the kind of kernel object for which a rule will be triggered to allow or deny an action"
8. Actions events further distinguished by action type, e.g. LANDLOCK_ACTION_FS_WRITE or subevent specific arg, e.g. ioctl request
9. How it works linux:security_init: Landlock LSM hooks are set up user application loads Landlock program(s) with bpf(2) and applies with seccomp(2) prog is triggered for events matching the program subtype prog allows (ret == 0) or denies access (ret != 0)
10. Applying a rule where prog_fd is the fd of the eBPF Landlock program prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0); seccomp(SECCOMP_PREPEND_LANDLOCK_RULE, 0, &prog_fd);
11. Writing a rule requires ... a subtype a handler program
12. The subtype SEC("subtype") static const union bpf_prog_subtype _subtype = { .landlock_rule = { .abi = 1, .event = LANDLOCK_SUBTYPE_EVENT_FS, .ability = LANDLOCK_SUBTYPE_ABILITY_DEBUG, } };
13. The handler program SEC("landlock1") static int landlock_fs_prog1(struct landlock_context *ctx) { char fmt_event_fs[] = "received event LANDLOCK_SUBTYPE_EVENT_FS\n"; char fmt_event_unknown[] = "received unknown event type\n"; if (ctx->event & LANDLOCK_SUBTYPE_EVENT_FS) { bpf_trace_printk(fmt_event_fs, sizeof(fmt_event_fs)); } else { // should not happen bpf_trace_printk(fmt_event_unknown, sizeof(fmt_event_unknown)); } return 0; // allow all }
14. Development LKML Patchset is based on net-next https://github.com/landlock-lsm/linux
15. Roadmap cgroups handling new eBPF map type for filesystem-related checks (map fsview) unprivileged mode source: https://landlock.io/talks/2017-09-14_landlock-lss.pdf
16. Thank you Questions? Slides can be found here soon: michael@kinvolk.io https://speakerdeck.com/schu
17. Resources https://landlock.io/ https://landlock.io/linux-doc/landlock-v7/security/landlock/index.html https://landlock.io/talks/2017-09-14_landlock-lss.pdf https://landlock.io/talks/2017-06-21_landlock-linuxkit-sig.pdf https://lkml.org/lkml/2017/8/20/192 https://man.openbsd.org/pledge.2 https://www.kernel.org/doc/Documentation/security/LSM.txt