On Fri, Nov 6, 2020 at 5:52 PM Martin KaFai Lau <kafai@xxxxxx> wrote:
>
> On Fri, Nov 06, 2020 at 05:14:14PM -0800, Andrii Nakryiko wrote:
> > On Fri, Nov 6, 2020 at 2:08 PM Martin KaFai Lau <kafai@xxxxxx> wrote:
> > >
> > > This patch enables the FENTRY/FEXIT/RAW_TP tracing program to use
> > > the bpf_sk_storage_(get|delete) helper, so those tracing programs
> > > can access the sk's bpf_local_storage and the later selftest
> > > will show some examples.
> > >
> > > The bpf_sk_storage is currently used in bpf-tcp-cc, tc,
> > > cg sockops...etc which is running either in softirq or
> > > task context.
> > >
> > > This patch adds bpf_sk_storage_get_tracing_proto and
> > > bpf_sk_storage_delete_tracing_proto. They will check
> > > in runtime that the helpers can only be called when serving
> > > softirq or running in a task context. That should enable
> > > most common tracing use cases on sk.
> > >
> > > During the load time, the new tracing_allowed() function
> > > will ensure the tracing prog using the bpf_sk_storage_(get|delete)
> > > helper is not tracing any *sk_storage*() function itself.
> > > The sk is passed as "void *" when calling into bpf_local_storage.
> > >
> > > Signed-off-by: Martin KaFai Lau <kafai@xxxxxx>
> > > ---
> > > include/net/bpf_sk_storage.h | 2 +
> > > kernel/trace/bpf_trace.c | 5 +++
> > > net/core/bpf_sk_storage.c | 73 ++++++++++++++++++++++++++++++++++++
> > > 3 files changed, 80 insertions(+)
> > >
> >
> > [...]
> >
> > > + switch (prog->expected_attach_type) {
> > > + case BPF_TRACE_RAW_TP:
> > > + /* bpf_sk_storage has no trace point */
> > > + return true;
> > > + case BPF_TRACE_FENTRY:
> > > + case BPF_TRACE_FEXIT:
> > > + btf_vmlinux = bpf_get_btf_vmlinux();
> > > + btf_id = prog->aux->attach_btf_id;
> > > + t = btf_type_by_id(btf_vmlinux, btf_id);
> > > + tname = btf_name_by_offset(btf_vmlinux, t->name_off);
> > > + return !strstr(tname, "sk_storage");
> >
> > I'm always feeling uneasy about substring checks... Also, KP just
> > fixed the issue with string-based checks for LSM. Can we use a
> > BTF_ID_SET of blacklisted functions instead?
> KP one is different. It accidentally whitelist-ed more than it should.
>
> It is a blacklist here. It is actually cleaner and safer to blacklist
> all functions with "sk_storage" and too pessimistic is fine here.
Fine for whom? Prefix check would be half-bad, but substring check is
horrible. Suddenly "task_storage" (and anything related) would be also
blacklisted. Let's do a prefix check at least.
>
> >
> > > + default:
> > > + return false;
> > > + }
> > > +
> > > + return false;
> > > +}
> > > +
> >
> > [...]
