Re: [RFC] audit support for BPF notification

cc-ing Petr Matousek jirka On Wed, Aug 14, 2019 at 09:33:34AM +0200, Jiri Olsa wrote: > hi, > Adding Vlad Dronov to the loop, because he asked > about this functionality some time ago. > > Vlad, the full thread can be found in here: > https://www.redhat.com/archives/linux-audit/2019-August/msg00004.html > > Any thoughts on this? > > thanks, > jirka > > On Mon, Aug 12, 2019 at 04:33:10PM +0200, Jiri Olsa wrote: > > On Mon, Aug 12, 2019 at 09:49:43AM -0400, Steve Grubb wrote: > > > On Monday, August 12, 2019 3:59:22 AM EDT Jiri Olsa wrote: > > > > On Fri, Aug 09, 2019 at 01:45:21PM -0400, Steve Grubb wrote: > > > > > Hello, > > > > > > > > > > On Friday, August 9, 2019 10:18:31 AM EDT Jiri Olsa wrote: > > > > > > I posted initial change that allows auditd to log BPF program > > > > > > > > > > > > load/unload events, it's in here: > > > > > > https://github.com/linux-audit/audit-userspace/pull/104 > > > > > > > > > > Thanks for the patch...but we probably should have talked a bit more > > > > > before undertaking this effort. We normally do not audit from user space > > > > > what happens in the kernel. Doing this can be racy and it keeps auditd > > > > > from doing the one job it has - which is to grab events and record them > > > > > to disk and send them out the realtime interface. > > > > > > > > > > > We tried to push pure AUDIT interface for BPF program notification, > > > > > > > > > > > > but it was denied, the discussion is in here: > > > > > > https://marc.info/?t=153866123200003&r=1&w=2 > > > > > > > > > > Hmm. The email I remember was here: > > > > > https://www.redhat.com/archives/linux-audit/2018-October/msg00053.html > > > > > > > > > > and was only 2 emails long with no answer to my question. :-) > > > > > > > > oops, sry about that, your question was: > > > > > I'm not sure exactly what the issue is. You can audit for specific > > > > > syscall > > > > > and argument. So, if you want to see loads, then you can make a rule > > > > > like: > > > > > > > > > > -a always,exit -F arch=b64 -S bpf -F a0=5 > > > > > > > > The problem with above for us is that we also: > > > > > > > > - need to log also other properties of the BPF program, > > > > which are not visible from BPF syscall arguments, like > > > > its ID, JIT status > > > > > > The way this is normally done is to add a supplemental record. For example, > > > when auditing the open syscall, we also get CWD & PATH supplemental records. > > > When auditing connect, we get a SOCKADDR supplemental record. We have > > > requirements around selective audit whereby the admin is in control of what > > > is selected for audit via audit rules. So, what one could do is set a rule > > > for the bpf syscall and then when it triggers, we get these other records > > > added to the bpf syscall event. > > > > right, that was the initial plan, but BPF guys wanted just > > single notification system without specific hooks for audit, > > so we ended up with perf specific interface > > > > > > or license info > > > > > > This ^^ is not a security issue. > > > > > > > > > > - need to see BPF program UNLOAD, which is not done > > > > via syscall, so those would be unvisible at all > > > > > > Is there a place in the kernel where this happens? I could see abnormal > > > termination being something we might want. Does the program go through > > > something like an exit syscall internally? > > > > it's happening in here (kernel/bpf/syscall.c): > > > > bpf_prog_put > > __bpf_prog_put > > { > > if (atomic_dec_and_test(&prog->aux->refcnt)) { > > perf_event_bpf_event(prog, PERF_BPF_EVENT_PROG_UNLOAD, 0); > > ... > > } > > > > BPF program is released when it drops the reference count, > > which is normally when its file descriptor is closed. > > > > However it might get pinned and stay alive even when the initial > > file descriptor is closed.. and then there's the networking world, > > which might have some other specific ways.. but it all ends up > > in bpf_prog_put and zero reference count. > > > > > > > > The outcome of the discussion was to use perf event interface > > > > > > for BPF notification and use it in some deamon.. audit was our > > > > > > first choice. > > > > > > > > > > > > thoughts? > > > > > > > > > > I'd like to understand what the basic problem is that needs to be solved. > > > > > > > > we need a way for administrators to see the history of loaded BPF > > > > programs, to help investigating issues related to BPF.. and the > > > > only BPF interface for this data is through perf ring buffer > > > > > > That is really not the audit way. Let's keep talking to see where this ends > > > up. > > > > Would you see some other auditing daemon/app in place for this kind of data? > > > > thanks, > > jirka