netdev - Re: [PATCH v4 bpf-next 15/20] bpf: Annotate context types

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <7092A2D7-BE2A-431F-B6A4-55BA963C36BF@fb.com>
Date:   Thu, 14 Nov 2019 22:55:37 +0000
From:   Song Liu <songliubraving@...com>
To:     Alexei Starovoitov <ast@...nel.org>
CC:     "davem@...emloft.net" <davem@...emloft.net>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        "x86@...nel.org" <x86@...nel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        Kernel Team <Kernel-team@...com>
Subject: Re: [PATCH v4 bpf-next 15/20] bpf: Annotate context types



> On Nov 14, 2019, at 10:57 AM, Alexei Starovoitov <ast@...nel.org> wrote:
> 
> Annotate BPF program context types with program-side type and kernel-side type.
> This type information is used by the verifier. btf_get_prog_ctx_type() is
> used in the later patches to verify that BTF type of ctx in BPF program matches to
> kernel expected ctx type. For example, the XDP program type is:
> BPF_PROG_TYPE(BPF_PROG_TYPE_XDP, xdp, struct xdp_md, struct xdp_buff)
> That means that XDP program should be written as:
> int xdp_prog(struct xdp_md *ctx) { ... }
> 
> Signed-off-by: Alexei Starovoitov <ast@...nel.org>
> 

[...]

> +	/* only compare that prog's ctx type name is the same as
> +	 * kernel expects. No need to compare field by field.
> +	 * It's ok for bpf prog to do:
> +	 * struct __sk_buff {};
> +	 * int socket_filter_bpf_prog(struct __sk_buff *skb)
> +	 * { // no fields of skb are ever used }
> +	 */
> +	if (strcmp(ctx_tname, tname))
> +		return NULL;

Do we need to check size of the two struct? I guess we should not 
allow something like

	struct __sk_buff {
		char data[REALLY_BIG_NUM]; 
	};
	int socket_filter_bpf_prog(struct __sk_buff *skb)
	{ /* access end of skb */ }

Or did I miss the size check? 

Thanks,
Song