[PATCH V2] bpf: security enhancement by limiting the offensive eBPF helpers

[Yonghong Song]

On 1/17/23 4:54 PM, Yi He wrote:
> The bpf_send_singal, bpf_send_singal_thread and bpf_override_return
> is similar to bpf_write_user and can affect userspace processes.
> Thus, these three helpers should also be restricted by security lockdown.
> 
> Signed-off-by: Yi He <clangllvm at 126.com>
> ---
>   V1 -> V2: add security lockdown to bpf_send_singal_thread and remove
> 	the unused LOCKDOWN_OFFENSIVE_BPF_MAX.
> 
>   include/linux/security.h | 2 ++
>   kernel/trace/bpf_trace.c | 9 ++++++---
>   2 files changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/security.h b/include/linux/security.h
> index 5b67f208f..42420e620 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -123,6 +123,8 @@ enum lockdown_reason {
>   	LOCKDOWN_DEBUGFS,
>   	LOCKDOWN_XMON_WR,
>   	LOCKDOWN_BPF_WRITE_USER,
> +	LOCKDOWN_BPF_SEND_SIGNAL,
> +	LOCKDOWN_BPF_OVERRIDE_RETURN,
>   	LOCKDOWN_DBG_WRITE_KERNEL,
>   	LOCKDOWN_RTAS_ERROR_INJECTION,
>   	LOCKDOWN_INTEGRITY_MAX,

Also, do you need to add an entry in lockdown_reasons in 
security/security.c?

Also add linux-security-module at vger.kernel.org so security experts can
chime in as well.


> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 3bbd3f0c8..fdb94868d 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -1463,9 +1463,11 @@ 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;
>   	case BPF_FUNC_send_signal_thread:
> -		return &bpf_send_signal_thread_proto;
> +		return security_locked_down(LOCKDOWN_BPF_SEND_SIGNAL) < 0 ?
> +		       NULL : &bpf_send_signal_thread_proto;
>   	case BPF_FUNC_perf_event_read_value:
>   		return &bpf_perf_event_read_value_proto;
>   	case BPF_FUNC_get_ns_current_pid_tgid:
> @@ -1531,7 +1533,8 @@ 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 ?