Re: [PATCH bpf-next v6 2/5] bpf: Expose bpf_get_socket_cookie to tracing programs

[Florent Revest]

On Fri, Jan 29, 2021 at 1:49 PM Daniel Borkmann <daniel@xxxxxxxxxxxxx> wrote:
>
> On 1/29/21 11:57 AM, Daniel Borkmann wrote:
> > On 1/27/21 10:01 PM, Andrii Nakryiko wrote:
> >> On Tue, Jan 26, 2021 at 10:36 AM Florent Revest <revest@xxxxxxxxxxxx> wrote:
> >>>
> >>> This needs a new helper that:
> >>> - can work in a sleepable context (using sock_gen_cookie)
> >>> - takes a struct sock pointer and checks that it's not NULL
> >>>
> >>> Signed-off-by: Florent Revest <revest@xxxxxxxxxxxx>
> >>> Acked-by: KP Singh <kpsingh@xxxxxxxxxx>
> >>> ---
> >>>   include/linux/bpf.h            |  1 +
> >>>   include/uapi/linux/bpf.h       |  8 ++++++++
> >>>   kernel/trace/bpf_trace.c       |  2 ++
> >>>   net/core/filter.c              | 12 ++++++++++++
> >>>   tools/include/uapi/linux/bpf.h |  8 ++++++++
> >>>   5 files changed, 31 insertions(+)
> >>>
> >>> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> >>> index 1aac2af12fed..26219465e1f7 100644
> >>> --- a/include/linux/bpf.h
> >>> +++ b/include/linux/bpf.h
> >>> @@ -1874,6 +1874,7 @@ extern const struct bpf_func_proto bpf_per_cpu_ptr_proto;
> >>>   extern const struct bpf_func_proto bpf_this_cpu_ptr_proto;
> >>>   extern const struct bpf_func_proto bpf_ktime_get_coarse_ns_proto;
> >>>   extern const struct bpf_func_proto bpf_sock_from_file_proto;
> >>> +extern const struct bpf_func_proto bpf_get_socket_ptr_cookie_proto;
> >>>
> >>>   const struct bpf_func_proto *bpf_tracing_func_proto(
> >>>          enum bpf_func_id func_id, const struct bpf_prog *prog);
> >>> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> >>> index 0b735c2729b2..5855c398d685 100644
> >>> --- a/include/uapi/linux/bpf.h
> >>> +++ b/include/uapi/linux/bpf.h
> >>> @@ -1673,6 +1673,14 @@ union bpf_attr {
> >>>    *     Return
> >>>    *             A 8-byte long unique number.
> >>>    *
> >>> + * u64 bpf_get_socket_cookie(void *sk)
> >>
> >> should the type be `struct sock *` then?
> >
> > Checking libbpf's generated bpf_helper_defs.h it generates:
> >
> > /*
> >   * bpf_get_socket_cookie
> >   *
> >   *      If the **struct sk_buff** pointed by *skb* has a known socket,
> >   *      retrieve the cookie (generated by the kernel) of this socket.
> >   *      If no cookie has been set yet, generate a new cookie. Once
> >   *      generated, the socket cookie remains stable for the life of the
> >   *      socket. This helper can be useful for monitoring per socket
> >   *      networking traffic statistics as it provides a global socket
> >   *      identifier that can be assumed unique.
> >   *
> >   * Returns
> >   *      A 8-byte long non-decreasing number on success, or 0 if the
> >   *      socket field is missing inside *skb*.
> >   */
> > static __u64 (*bpf_get_socket_cookie)(void *ctx) = (void *) 46;
> >
> > So in terms of helper comment it's picking up the description from the
> > `u64 bpf_get_socket_cookie(struct sk_buff *skb)` signature. With that
> > in mind it would likely make sense to add the actual `struct sock *` type
> > to the comment to make it more clear in here.
>
> One thought that still came to mind when looking over the series again, do
> we need to blacklist certain functions from bpf_get_socket_cookie() under
> tracing e.g. when attaching to, say fexit? For example, if sk_prot_free()
> would be temporary uninlined/exported for testing and bpf_get_socket_cookie()
> was invoked from a prog upon fexit where sock was already passed back to
> allocator, I presume there's risk of mem corruption, no?

Mh, this is interesting. I can try to add a deny list in v7 but I'm
not sure whether I'll be able to catch them all. I'm assuming that
__sk_destruct, sk_destruct, __sk_free, sk_free would be other
problematic functions but potentially there would be more.