Re: [PATCH bpf-next v2 2/2] bpf: Refactor bpf_tracing_func_proto() and remove bpf_get_probe_write_proto()

[Jiri Olsa <olsajiri@gmail.com>]

On Wed, Nov 27, 2024 at 12:10:01PM +0100, Marco Elver wrote:
> With bpf_get_probe_write_proto() no longer printing a message, we can
> avoid it being a special case with its own permission check.
> 
> Refactor bpf_tracing_func_proto() similar to bpf_base_func_proto() to
> have a section conditional on bpf_token_capable(CAP_SYS_ADMIN), where
> the proto for bpf_probe_write_user() is returned. Finally, remove the
> unnecessary bpf_get_probe_write_proto().
> 
> This simplifies the code, and adding additional CAP_SYS_ADMIN-only
> helpers in future avoids duplicating the same CAP_SYS_ADMIN check.
> 
> Suggested-by: Andrii Nakryiko <andrii@kernel.org>
> Signed-off-by: Marco Elver <elver@google.com>
> ---
> v2:
> * New patch.

Acked-by: Jiri Olsa <jolsa@kernel.org>

jirka

> ---
>  kernel/trace/bpf_trace.c | 30 ++++++++++++++++++------------
>  1 file changed, 18 insertions(+), 12 deletions(-)
> 
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 0ab56af2e298..d312b77993dc 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -357,14 +357,6 @@ static const struct bpf_func_proto bpf_probe_write_user_proto = {
>  	.arg3_type	= ARG_CONST_SIZE,
>  };
>  
> -static const struct bpf_func_proto *bpf_get_probe_write_proto(void)
> -{
> -	if (!capable(CAP_SYS_ADMIN))
> -		return NULL;
> -
> -	return &bpf_probe_write_user_proto;
> -}
> -
>  #define MAX_TRACE_PRINTK_VARARGS	3
>  #define BPF_TRACE_PRINTK_SIZE		1024
>  
> @@ -1417,6 +1409,12 @@ late_initcall(bpf_key_sig_kfuncs_init);
>  static const struct bpf_func_proto *
>  bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
>  {
> +	const struct bpf_func_proto *func_proto;
> +
> +	func_proto = bpf_base_func_proto(func_id, prog);
> +	if (func_proto)
> +		return func_proto;
> +
>  	switch (func_id) {
>  	case BPF_FUNC_map_lookup_elem:
>  		return &bpf_map_lookup_elem_proto;
> @@ -1458,9 +1456,6 @@ bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
>  		return &bpf_perf_event_read_proto;
>  	case BPF_FUNC_get_prandom_u32:
>  		return &bpf_get_prandom_u32_proto;
> -	case BPF_FUNC_probe_write_user:
> -		return security_locked_down(LOCKDOWN_BPF_WRITE_USER) < 0 ?
> -		       NULL : bpf_get_probe_write_proto();
>  	case BPF_FUNC_probe_read_user:
>  		return &bpf_probe_read_user_proto;
>  	case BPF_FUNC_probe_read_kernel:
> @@ -1539,7 +1534,18 @@ bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
>  	case BPF_FUNC_trace_vprintk:
>  		return bpf_get_trace_vprintk_proto();
>  	default:
> -		return bpf_base_func_proto(func_id, prog);
> +		break;
> +	}
> +
> +	if (!bpf_token_capable(prog->aux->token, CAP_SYS_ADMIN))
> +		return NULL;
> +
> +	switch (func_id) {
> +	case BPF_FUNC_probe_write_user:
> +		return security_locked_down(LOCKDOWN_BPF_WRITE_USER) < 0 ?
> +		       NULL : &bpf_probe_write_user_proto;
> +	default:
> +		return NULL;
>  	}
>  }
>  
> -- 
> 2.47.0.338.g60cca15819-goog
>