[PATCH v3 1/2] bpf: restore the ebpf program ID for BPF_AUDIT_UNLOAD and PERF_BPF_EVENT_PROG_UNLOAD

[Paul Moore]

On Fri, Jan 6, 2023 at 2:45 PM Stanislav Fomichev <sdf at google.com> wrote:
> On Fri, Jan 6, 2023 at 7:44 AM Paul Moore <paul at paul-moore.com> wrote:
> >
> > When changing the ebpf program put() routines to support being called
> > from within IRQ context the program ID was reset to zero prior to
> > calling the perf event and audit UNLOAD record generators, which
> > resulted in problems as the ebpf program ID was bogus (always zero).
> > This patch addresses this problem by removing an unnecessary call to
> > bpf_prog_free_id() in __bpf_prog_offload_destroy() and adjusting
> > __bpf_prog_put() to only call bpf_prog_free_id() after audit and perf
> > have finished their bpf program unload tasks in
> > bpf_prog_put_deferred().  For the record, no one can determine, or
> > remember, why it was necessary to free the program ID, and remove it
> > from the IDR, prior to executing bpf_prog_put_deferred();
> > regardless, both Stanislav and Alexei agree that the approach in this
> > patch should be safe.
> >
> > It is worth noting that when moving the bpf_prog_free_id() call, the
> > do_idr_lock parameter was forced to true as the ebpf devs determined
> > this was the correct as the do_idr_lock should always be true.  The
> > do_idr_lock parameter will be removed in a follow-up patch, but it
> > was kept here to keep the patch small in an effort to ease any stable
> > backports.
> >
> > I also modified the bpf_audit_prog() logic used to associate the
> > AUDIT_BPF record with other associated records, e.g. @ctx != NULL.
> > Instead of keying off the operation, it now keys off the execution
> > context, e.g. '!in_irg && !irqs_disabled()', which is much more
> > appropriate and should help better connect the UNLOAD operations with
> > the associated audit state (other audit records).
> >
> > Cc: stable at vger.kernel.org
> > Fixes: d809e134be7a ("bpf: Prepare bpf_prog_put() to be called from irq context.")
> > Reported-by: Burn Alting <burn.alting at iinet.net.au>
> > Reported-by: Jiri Olsa <olsajiri at gmail.com>
> > Suggested-by: Stanislav Fomichev <sdf at google.com>
> > Suggested-by: Alexei Starovoitov <alexei.starovoitov at gmail.com>
> > Signed-off-by: Paul Moore <paul at paul-moore.com>
>
> Acked-by: Stanislav Fomichev <sdf at google.com>
>
> Thank you! There might be a chance it breaks test_offload.py (I don't
> remember whether it checks this prog-is-removed-from-id part or not),
> but I don't think it's fair to ask to address it :-)
> Since it doesn't trigger in CI, I'll take another look next week when
> doing a respin of my 'xdp-hints' series.

No problem, I'm glad we found a solution that works for everyone; and
thank you for chasing down any test changes that may be necessary.

I'd like to get this patch into Linus' tree sooner rather than later
as it fixes a kinda ugly problem, would you be okay if this went in
via the bpf tree?  With the appropriate ACKs I could send it to Linus
via the audit tree, but I think it would be much better to send it via
the bpf/netdev tree.

-- 
paul-moore.com