netdev - Re: [PATCH bpf-next v2] bpf: bpf_{g,s}etsockopt for struct bpf

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Message-ID: <640e7fd3-4059-5ff8-f9ed-09b1becd0f7b@iogearbox.net>
Date:   Thu, 30 Apr 2020 01:08:28 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Stanislav Fomichev <sdf@...gle.com>, netdev@...r.kernel.org,
        bpf@...r.kernel.org
Cc:     davem@...emloft.net, ast@...nel.org,
        John Fastabend <john.fastabend@...il.com>,
        Martin KaFai Lau <kafai@...com>
Subject: Re: [PATCH bpf-next v2] bpf: bpf_{g,s}etsockopt for struct bpf_sock

On 4/29/20 7:05 PM, Stanislav Fomichev wrote:
> Currently, bpf_getsocktop and bpf_setsockopt helpers operate on the
> 'struct bpf_sock_ops' context in BPF_PROG_TYPE_SOCK_OPS program.
> Let's generalize them and make the first argument be 'struct bpf_sock'.
> That way, in the future, we can allow those helpers in more places.
> 
> BPF_PROG_TYPE_SOCK_OPS still has the existing helpers that operate
> on 'struct bpf_sock_ops', but we add new bpf_{g,s}etsockopt that work
> on 'struct bpf_sock'. [Alternatively, for BPF_PROG_TYPE_SOCK_OPS,
> we can enable them both and teach verifier to pick the right one
> based on the context (bpf_sock_ops vs bpf_sock).]
> 
> As an example, let's allow those 'struct bpf_sock' based helpers to
> be called from the BPF_CGROUP_INET{4,6}_CONNECT hooks. That way
> we can override CC before the connection is made.
> 
> v2:
> * s/BPF_PROG_TYPE_CGROUP_SOCKOPT/BPF_PROG_TYPE_SOCK_OPS/
> 
> Acked-by: John Fastabend <john.fastabend@...il.com>
> Acked-by: Martin KaFai Lau <kafai@...com>
> Signed-off-by: Stanislav Fomichev <sdf@...gle.com>
[...]
> +BPF_CALL_5(bpf_setsockopt, struct sock *, sk,
> +	   int, level, int, optname, char *, optval, int, optlen)
> +{
> +	u32 flags = 0;
> +	return _bpf_setsockopt(sk, level, optname, optval, optlen, flags);
> +}
> +
> +static const struct bpf_func_proto bpf_setsockopt_proto = {
> +	.func		= bpf_setsockopt,
> +	.gpl_only	= false,
> +	.ret_type	= RET_INTEGER,
> +	.arg1_type	= ARG_PTR_TO_SOCKET,
> +	.arg2_type	= ARG_ANYTHING,
> +	.arg3_type	= ARG_ANYTHING,
> +	.arg4_type	= ARG_PTR_TO_MEM,
> +	.arg5_type	= ARG_CONST_SIZE,
> +};
> +
> +BPF_CALL_5(bpf_getsockopt, struct sock *, sk,
> +	   int, level, int, optname, char *, optval, int, optlen)
> +{
> +	return _bpf_getsockopt(sk, level, optname, optval, optlen);
> +}
> +
>   static const struct bpf_func_proto bpf_getsockopt_proto = {
>   	.func		= bpf_getsockopt,
>   	.gpl_only	= false,
>   	.ret_type	= RET_INTEGER,
> +	.arg1_type	= ARG_PTR_TO_SOCKET,
> +	.arg2_type	= ARG_ANYTHING,
> +	.arg3_type	= ARG_ANYTHING,
> +	.arg4_type	= ARG_PTR_TO_UNINIT_MEM,
> +	.arg5_type	= ARG_CONST_SIZE,
> +};
> +
[...]
> @@ -6043,6 +6098,22 @@ sock_addr_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
>   		return &bpf_sk_storage_get_proto;
>   	case BPF_FUNC_sk_storage_delete:
>   		return &bpf_sk_storage_delete_proto;
> +	case BPF_FUNC_setsockopt:
> +		switch (prog->expected_attach_type) {
> +		case BPF_CGROUP_INET4_CONNECT:
> +		case BPF_CGROUP_INET6_CONNECT:
> +			return &bpf_setsockopt_proto;

Hm, I'm not sure this is safe. In the sock_addr_func_proto() we also have
other helpers callable from connect hooks like sk_lookup_{tcp,udp} which
return a PTR_TO_SOCKET_OR_NULL, and now we can pass those sockets also into
bpf_{get,set}sockopt() helper after lookup to change various sk related stuff
but w/o being under lock. Doesn't the sock_owned_by_me() yell here at minimum
(I'd expect so)?

> +		default:
> +			return NULL;
> +		}
> +	case BPF_FUNC_getsockopt:
> +		switch (prog->expected_attach_type) {
> +		case BPF_CGROUP_INET4_CONNECT:
> +		case BPF_CGROUP_INET6_CONNECT:
> +			return &bpf_getsockopt_proto;
> +		default:
> +			return NULL;
> +		}
>   	default: