Re: [PATCH] bpf: security enhancement by limiting the offensive eBPF helpers

[Yonghong Song <yhs@meta.com>]

On 1/17/23 7:12 AM, WritePaper wrote:
> The bpf_send_singal and bpf_override_return is similar to
> bpf_write_user and can affect userspace processes. Thus, these two
> helpers should also be constraint by security lockdown.
> 
> Signed-off-by: WritePaper <clangllvm@126.com>
> ---
>   include/linux/security.h | 3 +++
>   kernel/trace/bpf_trace.c | 6 ++++--
>   2 files changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/security.h b/include/linux/security.h
> index 5b67f208f..cb90b2860 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -123,6 +123,9 @@ enum lockdown_reason {
>   	LOCKDOWN_DEBUGFS,
>   	LOCKDOWN_XMON_WR,
>   	LOCKDOWN_BPF_WRITE_USER,
> +	LOCKDOWN_BPF_SEND_SIGNAL,
> +	LOCKDOWN_BPF_OVERRIDE_RETURN,
> +	LOCKDOWN_OFFENSIVE_BPF_MAX,

LOCKDOWN_OFFENSIVE_BPF_MAX is not used.

>   	LOCKDOWN_DBG_WRITE_KERNEL,
>   	LOCKDOWN_RTAS_ERROR_INJECTION,
>   	LOCKDOWN_INTEGRITY_MAX,
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 3bbd3f0c8..3a80f4b6f 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -1463,7 +1463,8 @@ bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
>   		return &bpf_cgrp_storage_delete_proto;
>   #endif
>   	case BPF_FUNC_send_signal:
> -		return &bpf_send_signal_proto;
> +		return security_locked_down(LOCKDOWN_BPF_SEND_SIGNAL) < 0 ?
> +		       NULL : &bpf_send_signal_proto;

You should add the same security_locked_down(LOCKDOWN_BPF_SEND_SIGNAL) 
check with below bpf_send_signal_thread() helper.

>   	case BPF_FUNC_send_signal_thread:
>   		return &bpf_send_signal_thread_proto;
>   	case BPF_FUNC_perf_event_read_value:
> @@ -1531,7 +1532,8 @@ kprobe_prog_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
>   		return &bpf_get_stack_proto;
>   #ifdef CONFIG_BPF_KPROBE_OVERRIDE
>   	case BPF_FUNC_override_return:
> -		return &bpf_override_return_proto;
> +		return security_locked_down(LOCKDOWN_BPF_OVERRIDE_RETURN) < 0 ?
> +		       NULL : &bpf_override_return_proto;
>   #endif
>   	case BPF_FUNC_get_func_ip:
>   		return prog->expected_attach_type == BPF_TRACE_KPROBE_MULTI ?