On Mon, Jul 01, 2019 at 06:59:13PM -0700, Andy Lutomirski wrote: > I think I'm understanding your motivation. You're not trying to make > bpf() generically usable without privilege -- you're trying to create > a way to allow certain users to access dangerous bpf functionality > within some limits. > > That's a perfectly fine goal, but I think you're reinventing the > wheel, and the wheel you're reinventing is quite complicated and > already exists. I think you should teach bpftool to be secure when > installed setuid root or with fscaps enabled and put your policy in > bpftool. If you want to harden this a little bit, it would seem > entirely reasonable to add a new CAP_BPF_ADMIN and change some, but > not all, of the capable() checks to check CAP_BPF_ADMIN instead of the > capabilities that they currently check. If finer grained controls are wanted, it does seem like the /dev/bpf path makes the most sense. open, request abilities, use fd. The open can be mediated by DAC and LSM. The request can be mediated by LSM. This provides a way to add policy at the LSM level and at the tool level. (i.e. For tool-level controls: leave LSM wide open, make /dev/bpf owned by "bpfadmin" and bpftool becomes setuid "bpfadmin". For fine-grained controls, leave /dev/bpf wide open and add policy to SELinux, etc.) With only a new CAP, you don't get the fine-grained controls. (The "request abilities" part is the key there.) -- Kees Cook
