netdev - Re: [PATCH net-next] bpf: expose sk_priority through struct bpf_sock

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Date:   Fri, 10 Nov 2017 22:07:13 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Vlad Dumitrescu <vlad@...itrescu.ro>, davem@...emloft.net,
        ast@...com, brakmo@...com
Cc:     netdev@...r.kernel.org, kraigatgoog@...il.com
Subject: Re: [PATCH net-next] bpf: expose sk_priority through struct
 bpf_sock_ops

On 11/10/2017 08:17 PM, Vlad Dumitrescu wrote:
> From: Vlad Dumitrescu <vladum@...gle.com>
> 
> Allows BPF_PROG_TYPE_SOCK_OPS programs to read sk_priority.
> 
> Signed-off-by: Vlad Dumitrescu <vladum@...gle.com>
> ---
>   include/uapi/linux/bpf.h       |  1 +
>   net/core/filter.c              | 11 +++++++++++
>   tools/include/uapi/linux/bpf.h |  1 +
>   3 files changed, 13 insertions(+)
> 
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index e880ae6434ee..9757a2002513 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -947,6 +947,7 @@ struct bpf_sock_ops {
>   	__u32 local_ip6[4];	/* Stored in network byte order */
>   	__u32 remote_port;	/* Stored in network byte order */
>   	__u32 local_port;	/* stored in host byte order */
> +	__u32 priority;
>   };
>   
>   /* List of known BPF sock_ops operators.
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 61c791f9f628..a6329642d047 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -4449,6 +4449,17 @@ static u32 sock_ops_convert_ctx_access(enum bpf_access_type type,
>   		*insn++ = BPF_LDX_MEM(BPF_H, si->dst_reg, si->dst_reg,
>   				      offsetof(struct sock_common, skc_num));
>   		break;
> +
> +	case offsetof(struct bpf_sock_ops, priority):
> +		BUILD_BUG_ON(FIELD_SIZEOF(struct sock, sk_priority) != 4);
> +
> +		*insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(
> +						struct bpf_sock_ops_kern, sk),
> +				      si->dst_reg, si->src_reg,
> +				      offsetof(struct bpf_sock_ops_kern, sk));
> +		*insn++ = BPF_LDX_MEM(BPF_W, si->dst_reg, si->dst_reg,
> +				      offsetof(struct sock, sk_priority));
> +		break;

Hm, I don't think this would work, I actually think your initial patch was ok.
bpf_setsockopt() as well as bpf_getsockopt() check for sk_fullsock(sk) right
before accessing options on either socket or TCP level, and bail out with error
otherwise; in such cases we'd read something else here and assume it's sk_priority.

>   	}
>   	return insn - insn_buf;
>   }
> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> index e880ae6434ee..9757a2002513 100644
> --- a/tools/include/uapi/linux/bpf.h
> +++ b/tools/include/uapi/linux/bpf.h
> @@ -947,6 +947,7 @@ struct bpf_sock_ops {
>   	__u32 local_ip6[4];	/* Stored in network byte order */
>   	__u32 remote_port;	/* Stored in network byte order */
>   	__u32 local_port;	/* stored in host byte order */
> +	__u32 priority;
>   };
>   
>   /* List of known BPF sock_ops operators.
>