netdev - Re: [PATCH bpf-next 09/10] bpf: disallow bpf_probe_read[

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Date:   Tue, 8 Oct 2019 22:29:08 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Alexei Starovoitov <ast@...nel.org>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Daniel Borkmann <daniel@...earbox.net>, x86@...nel.org,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH bpf-next 09/10] bpf: disallow bpf_probe_read[_str] helpers

On Fri, Oct 4, 2019 at 10:04 PM Alexei Starovoitov <ast@...nel.org> wrote:
>
> Disallow bpf_probe_read() and bpf_probe_read_str() helpers in
> raw_tracepoint bpf programs that use in-kernel BTF to track
> types of memory accesses.
>
> Signed-off-by: Alexei Starovoitov <ast@...nel.org>
> ---
>  kernel/trace/bpf_trace.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 52f7e9d8c29b..7c607f79f1bb 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -700,6 +700,8 @@ tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
>         case BPF_FUNC_map_peek_elem:
>                 return &bpf_map_peek_elem_proto;
>         case BPF_FUNC_probe_read:
> +               if (prog->expected_attach_type)
> +                       return NULL;

This can unintentionally disable bpf_probe_read/bpf_probe_read_str for
non-raw_tp programs that happened to specify non-zero
expected_attach_type, which we don't really validate for
kprobe/tp/perf_event/etc. So how about passing program type into
tracing_func_proto() so that we can have more granular control?

>                 return &bpf_probe_read_proto;
>         case BPF_FUNC_ktime_get_ns:
>                 return &bpf_ktime_get_ns_proto;
> @@ -728,6 +730,8 @@ tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
>         case BPF_FUNC_get_prandom_u32:
>                 return &bpf_get_prandom_u32_proto;
>         case BPF_FUNC_probe_read_str:
> +               if (prog->expected_attach_type)
> +                       return NULL;
>                 return &bpf_probe_read_str_proto;
>  #ifdef CONFIG_CGROUPS
>         case BPF_FUNC_get_current_cgroup_id:
> --
> 2.20.0
>