netdev - Re: [PATCH bpf-next 07/11] bpf: make sure to clear unused fields in tunnel/xfrm state fetch

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Date:   Wed, 30 May 2018 10:15:33 -0700
From:   Song Liu <liu.song.a23@...il.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Networking <netdev@...r.kernel.org>
Subject: Re: [PATCH bpf-next 07/11] bpf: make sure to clear unused fields in
 tunnel/xfrm state fetch

On Sun, May 27, 2018 at 5:43 PM, Daniel Borkmann <daniel@...earbox.net> wrote:
> Since the remaining bits are not filled in struct bpf_tunnel_key
> resp. struct bpf_xfrm_state and originate from uninitialized stack
> space, we should make sure to clear them before handing control
> back to the program.
>
> Also add a padding element to struct bpf_xfrm_state for future use
> similar as we have in struct bpf_tunnel_key and clear it as well.
>
>   struct bpf_xfrm_state {
>       __u32                      reqid;            /*     0     4 */
>       __u32                      spi;              /*     4     4 */
>       __u16                      family;           /*     8     2 */
>
>       /* XXX 2 bytes hole, try to pack */
>
>       union {
>           __u32              remote_ipv4;          /*           4 */
>           __u32              remote_ipv6[4];       /*          16 */
>       };                                           /*    12    16 */
>
>       /* size: 28, cachelines: 1, members: 4 */
>       /* sum members: 26, holes: 1, sum holes: 2 */
>       /* last cacheline: 28 bytes */
>   };
>
> Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
> Acked-by: Alexei Starovoitov <ast@...nel.org>

Acked-by: Song Liu <songliubraving@...com>

> ---
>  include/uapi/linux/bpf.h | 3 ++-
>  net/core/filter.c        | 6 ++++++
>  2 files changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index e2853aa..7108711 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -2214,7 +2214,7 @@ struct bpf_tunnel_key {
>         };
>         __u8 tunnel_tos;
>         __u8 tunnel_ttl;
> -       __u16 tunnel_ext;
> +       __u16 tunnel_ext;       /* Padding, future use. */
>         __u32 tunnel_label;
>  };
>
> @@ -2225,6 +2225,7 @@ struct bpf_xfrm_state {
>         __u32 reqid;
>         __u32 spi;      /* Stored in network byte order */
>         __u16 family;
> +       __u16 ext;      /* Padding, future use. */
>         union {
>                 __u32 remote_ipv4;      /* Stored in network byte order */
>                 __u32 remote_ipv6[4];   /* Stored in network byte order */
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 717c740..5ceb5e6 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -3445,6 +3445,7 @@ BPF_CALL_4(bpf_skb_get_tunnel_key, struct sk_buff *, skb, struct bpf_tunnel_key
>         to->tunnel_id = be64_to_cpu(info->key.tun_id);
>         to->tunnel_tos = info->key.tos;
>         to->tunnel_ttl = info->key.ttl;
> +       to->tunnel_ext = 0;
>
>         if (flags & BPF_F_TUNINFO_IPV6) {
>                 memcpy(to->remote_ipv6, &info->key.u.ipv6.src,
> @@ -3452,6 +3453,8 @@ BPF_CALL_4(bpf_skb_get_tunnel_key, struct sk_buff *, skb, struct bpf_tunnel_key
>                 to->tunnel_label = be32_to_cpu(info->key.label);
>         } else {
>                 to->remote_ipv4 = be32_to_cpu(info->key.u.ipv4.src);
> +               memset(&to->remote_ipv6[1], 0, sizeof(__u32) * 3);
> +               to->tunnel_label = 0;
>         }
>
>         if (unlikely(size != sizeof(struct bpf_tunnel_key)))
> @@ -4047,11 +4050,14 @@ BPF_CALL_5(bpf_skb_get_xfrm_state, struct sk_buff *, skb, u32, index,
>         to->reqid = x->props.reqid;
>         to->spi = x->id.spi;
>         to->family = x->props.family;
> +       to->ext = 0;
> +
>         if (to->family == AF_INET6) {
>                 memcpy(to->remote_ipv6, x->props.saddr.a6,
>                        sizeof(to->remote_ipv6));
>         } else {
>                 to->remote_ipv4 = x->props.saddr.a4;
> +               memset(&to->remote_ipv6[1], 0, sizeof(__u32) * 3);
>         }
>
>         return 0;
> --
> 2.9.5
>