On Wed, Apr 12, 2023 at 12:33 AM Andrii Nakryiko <andrii@xxxxxxxxxx> wrote: > > Add new LSM hooks, bpf_map_create_security and bpf_btf_load_security, which > are meant to allow highly-granular LSM-based control over the usage of BPF > subsytem. Specifically, to control the creation of BPF maps and BTF data > objects, which are fundamental building blocks of any modern BPF application. > > These new hooks are able to override default kernel-side CAP_BPF-based (and > sometimes CAP_NET_ADMIN-based) permission checks. It is now possible to > implement LSM policies that could granularly enforce more restrictions on > a per-BPF map basis (beyond checking coarse CAP_BPF/CAP_NET_ADMIN > capabilities), but also, importantly, allow to *bypass kernel-side > enforcement* of CAP_BPF/CAP_NET_ADMIN checks for trusted applications and use > cases. One of the hallmarks of the LSM has always been that it is non-authoritative: it cannot unilaterally grant access, it can only restrict what would have been otherwise permitted on a traditional Linux system. Put another way, a LSM should not undermine the Linux discretionary access controls, e.g. capabilities. If there is a problem with the eBPF capability-based access controls, that problem needs to be addressed in how the core eBPF code implements its capability checks, not by modifying the LSM mechanism to bypass these checks. -- paul-moore.com
