On Tue, Jul 23, 2019 at 5:33 AM Toke Høiland-Jørgensen <toke@xxxxxxxxxx> wrote:
>
> Petar Penkov <ppenkov.kernel@xxxxxxxxx> writes:
>
> > From: Petar Penkov <ppenkov@xxxxxxxxxx>
> >
> > This helper function allows BPF programs to try to generate SYN
> > cookies, given a reference to a listener socket. The function works
> > from XDP and with an skb context since bpf_skc_lookup_tcp can lookup a
> > socket in both cases.
> >
> > Signed-off-by: Petar Penkov <ppenkov@xxxxxxxxxx>
> > Suggested-by: Eric Dumazet <edumazet@xxxxxxxxxx>
> > ---
> > include/uapi/linux/bpf.h | 30 ++++++++++++++++-
> > net/core/filter.c | 73 ++++++++++++++++++++++++++++++++++++++++
> > 2 files changed, 102 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> > index 6f68438aa4ed..20baee7b2219 100644
> > --- a/include/uapi/linux/bpf.h
> > +++ b/include/uapi/linux/bpf.h
> > @@ -2713,6 +2713,33 @@ union bpf_attr {
> > * **-EPERM** if no permission to send the *sig*.
> > *
> > * **-EAGAIN** if bpf program can try again.
> > + *
> > + * s64 bpf_tcp_gen_syncookie(struct bpf_sock *sk, void *iph, u32 iph_len, struct tcphdr *th, u32 th_len)
> > + * Description
> > + * Try to issue a SYN cookie for the packet with corresponding
> > + * IP/TCP headers, *iph* and *th*, on the listening socket in *sk*.
> > + *
> > + * *iph* points to the start of the IPv4 or IPv6 header, while
> > + * *iph_len* contains **sizeof**\ (**struct iphdr**) or
> > + * **sizeof**\ (**struct ip6hdr**).
> > + *
> > + * *th* points to the start of the TCP header, while *th_len*
> > + * contains the length of the TCP header.
> > + *
> > + * Return
> > + * On success, lower 32 bits hold the generated SYN cookie in
> > + * followed by 16 bits which hold the MSS value for that cookie,
> > + * and the top 16 bits are unused.
> > + *
> > + * On failure, the returned value is one of the following:
> > + *
> > + * **-EINVAL** SYN cookie cannot be issued due to error
> > + *
> > + * **-ENOENT** SYN cookie should not be issued (no SYN flood)
> > + *
> > + * **-ENOTSUPP** kernel configuration does not enable SYN
> > cookies
>
> nit: This should be EOPNOTSUPP - the other one is for NFS...
Will correct this in a v2, thanks for catching that!
>
> > + *
> > + * **-EPROTONOSUPPORT** IP packet version is not 4 or 6
> > */
> > #define __BPF_FUNC_MAPPER(FN) \
> > FN(unspec), \
> > @@ -2824,7 +2851,8 @@ union bpf_attr {
> > FN(strtoul), \
> > FN(sk_storage_get), \
> > FN(sk_storage_delete), \
> > - FN(send_signal),
> > + FN(send_signal), \
> > + FN(tcp_gen_syncookie),
> >
> > /* integer value in 'imm' field of BPF_CALL instruction selects which helper
> > * function eBPF program intends to call
> > diff --git a/net/core/filter.c b/net/core/filter.c
> > index 47f6386fb17a..92114271eff6 100644
> > --- a/net/core/filter.c
> > +++ b/net/core/filter.c
> > @@ -5850,6 +5850,75 @@ static const struct bpf_func_proto bpf_tcp_check_syncookie_proto = {
> > .arg5_type = ARG_CONST_SIZE,
> > };
> >
> > +BPF_CALL_5(bpf_tcp_gen_syncookie, struct sock *, sk, void *, iph, u32, iph_len,
> > + struct tcphdr *, th, u32, th_len)
> > +{
> > +#ifdef CONFIG_SYN_COOKIES
> > + u32 cookie;
> > + u16 mss;
> > +
> > + if (unlikely(th_len < sizeof(*th) || th_len != th->doff * 4))
> > + return -EINVAL;
> > +
> > + if (sk->sk_protocol != IPPROTO_TCP || sk->sk_state != TCP_LISTEN)
> > + return -EINVAL;
> > +
> > + if (!sock_net(sk)->ipv4.sysctl_tcp_syncookies)
> > + return -ENOENT;
> > +
> > + if (!th->syn || th->ack || th->fin || th->rst)
> > + return -EINVAL;
> > +
> > + if (unlikely(iph_len < sizeof(struct iphdr)))
> > + return -EINVAL;
> > +
> > + /* Both struct iphdr and struct ipv6hdr have the version field at the
> > + * same offset so we can cast to the shorter header (struct iphdr).
> > + */
> > + switch (((struct iphdr *)iph)->version) {
> > + case 4:
> > + if (sk->sk_family == AF_INET6 && sk->sk_ipv6only)
> > + return -EINVAL;
> > +
> > + mss = tcp_v4_get_syncookie(sk, iph, th, &cookie);
> > + break;
> > +
> > +#if IS_BUILTIN(CONFIG_IPV6)
> > + case 6:
> > + if (unlikely(iph_len < sizeof(struct ipv6hdr)))
> > + return -EINVAL;
> > +
> > + if (sk->sk_family != AF_INET6)
> > + return -EINVAL;
> > +
> > + mss = tcp_v6_get_syncookie(sk, iph, th, &cookie);
> > + break;
> > +#endif /* CONFIG_IPV6 */
> > +
> > + default:
> > + return -EPROTONOSUPPORT;
> > + }
> > + if (mss <= 0)
> > + return -ENOENT;
> > +
> > + return cookie | ((u64)mss << 32);
> > +#else
> > + return -ENOTSUPP;
>
> See above
>
> > +#endif /* CONFIG_SYN_COOKIES */
> > +}
> > +
> > +static const struct bpf_func_proto bpf_tcp_gen_syncookie_proto = {
> > + .func = bpf_tcp_gen_syncookie,
> > + .gpl_only = true, /* __cookie_v*_init_sequence() is GPL */
> > + .pkt_access = true,
> > + .ret_type = RET_INTEGER,
> > + .arg1_type = ARG_PTR_TO_SOCK_COMMON,
> > + .arg2_type = ARG_PTR_TO_MEM,
> > + .arg3_type = ARG_CONST_SIZE,
> > + .arg4_type = ARG_PTR_TO_MEM,
> > + .arg5_type = ARG_CONST_SIZE,
> > +};
> > +
> > #endif /* CONFIG_INET */
> >
> > bool bpf_helper_changes_pkt_data(void *func)
> > @@ -6135,6 +6204,8 @@ tc_cls_act_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
> > return &bpf_tcp_check_syncookie_proto;
> > case BPF_FUNC_skb_ecn_set_ce:
> > return &bpf_skb_ecn_set_ce_proto;
> > + case BPF_FUNC_tcp_gen_syncookie:
> > + return &bpf_tcp_gen_syncookie_proto;
> > #endif
> > default:
> > return bpf_base_func_proto(func_id);
> > @@ -6174,6 +6245,8 @@ xdp_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
> > return &bpf_xdp_skc_lookup_tcp_proto;
> > case BPF_FUNC_tcp_check_syncookie:
> > return &bpf_tcp_check_syncookie_proto;
> > + case BPF_FUNC_tcp_gen_syncookie:
> > + return &bpf_tcp_gen_syncookie_proto;
> > #endif
> > default:
> > return bpf_base_func_proto(func_id);
> > --
> > 2.22.0.657.g960e92d24f-goog
