Re: [PATCH v2] bpf: restore the ebpf program ID for BPF_AUDIT_UNLOAD and PERF_BPF_EVENT_PROG_UNLOAD

On December 26, 2022 10:35:49 PM Stanislav Fomichev <stfomichev(a)yandex.ru&gt; wrote: >> On Fri, Dec 23, 2022 at 5:49 PM Stanislav Fomichev <sdf(a)google.com&gt; wrote: >> get_func_ip() */ >>>> - tstamp_type_access:1; /* Accessed >>>> __sk_buff->tstamp_type */ >>>> + tstamp_type_access:1, /* Accessed >>>> __sk_buff->tstamp_type */ >>>> + valid_id:1; /* Is bpf_prog::aux::__id valid? */ >>>> enum bpf_prog_type type; /* Type of BPF program */ >>>> enum bpf_attach_type expected_attach_type; /* For some prog types */ >>>> u32 len; /* Number of filter blocks */ >>>> @@ -1688,6 +1689,12 @@ void bpf_prog_inc(struct bpf_prog *prog); >>>> struct bpf_prog * __must_check bpf_prog_inc_not_zero(struct bpf_prog *prog); >>>> void bpf_prog_put(struct bpf_prog *prog); >>>> >>>> +static inline u32 bpf_prog_get_id(const struct bpf_prog *prog) >>>> +{ >>>> + if (WARN(!prog->valid_id, "Attempting to use an invalid eBPF program")) >>>> + return 0; >>>> + return prog->aux->__id; >>>> +} >>> >>> I'm still missing why we need to have this WARN and have a check at all. >>> IIUC, we're actually too eager in resetting the id to 0, and need to >>> keep that stale id around at least for perf/audit. >>> Why not have a flag only to protect against double-idr_remove >>> bpf_prog_free_id and keep the rest as is? >>> Which places are we concerned about that used to report id=0 but now >>> would report stale id? >> >> What double-idr_remove are you concerned about? >> bpf_prog_by_id() is doing bpf_prog_inc_not_zero >> while __bpf_prog_put just dropped it to zero. > > (traveling, sending from an untested setup, hope it reaches everyone) > > There is a call to bpf_prog_free_id from __bpf_prog_offload_destroy which > tries to make offloaded program disappear from the idr when the netdev > goes offline. So I'm assuming that '!prog->aux->id' check in bpf_prog_free_id > is to handle that case where we do bpf_prog_free_id much earlier than the > rest of the __bpf_prog_put stuff. > >> Maybe just move bpf_prog_free_id() into bpf_prog_put_deferred() >> after perf_event_bpf_event and bpf_audit_prog ? >> Probably can remove the obsolete do_idr_lock bool flag as >> separate patch? > > +1 on removing do_idr_lock separately. > >> Much simpler fix and no code churn. >> Both valid_id and saved_id approaches have flaws. > > Given the __bpf_prog_offload_destroy path above, we still probably need > some flag to indicate that the id has been already removed from the idr? So what do you guys want in a patch? Is there a consensus on what you would merge to fix this bug/regression?