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Date: Tue, 28 Feb 2023 11:37:16 -0800
From: Stanislav Fomichev <sdf@...gle.com>
To: Daniel Xu <dxu@...uu.xyz>
Cc: kuba@...nel.org, edumazet@...gle.com, davem@...emloft.net,
dsahern@...nel.org, pabeni@...hat.com,
linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
bpf@...r.kernel.org
Subject: Re: [PATCH bpf-next v2 3/8] bpf, net, frags: Add bpf_ip_check_defrag()
kfunc
On 02/27, Daniel Xu wrote:
> This kfunc is used to defragment IPv4 packets. The idea is that if you
> see a fragmented packet, you call this kfunc. If the kfunc returns 0,
> then the skb has been updated to contain the entire reassembled packet.
> If the kfunc returns an error (most likely -EINPROGRESS), then it means
> the skb is part of a yet-incomplete original packet. A reasonable
> response to -EINPROGRESS is to drop the packet, as the ip defrag
> infrastructure is already hanging onto the frag for future reassembly.
> Care has been taken to ensure the prog skb remains valid no matter what
> the underlying ip_check_defrag() call does. This is in contrast to
> ip_defrag(), which may consume the skb if the skb is part of a
> yet-incomplete original packet.
> So far this kfunc is only callable from TC clsact progs.
> Signed-off-by: Daniel Xu <dxu@...uu.xyz>
> ---
> include/net/ip.h | 11 +++++
> net/ipv4/Makefile | 1 +
> net/ipv4/ip_fragment.c | 2 +
> net/ipv4/ip_fragment_bpf.c | 98 ++++++++++++++++++++++++++++++++++++++
> 4 files changed, 112 insertions(+)
> create mode 100644 net/ipv4/ip_fragment_bpf.c
> diff --git a/include/net/ip.h b/include/net/ip.h
> index c3fffaa92d6e..f3796b1b5cac 100644
> --- a/include/net/ip.h
> +++ b/include/net/ip.h
> @@ -680,6 +680,7 @@ enum ip_defrag_users {
> IP_DEFRAG_VS_FWD,
> IP_DEFRAG_AF_PACKET,
> IP_DEFRAG_MACVLAN,
> + IP_DEFRAG_BPF,
> };
> /* Return true if the value of 'user' is between 'lower_bond'
> @@ -693,6 +694,16 @@ static inline bool ip_defrag_user_in_between(u32
> user,
> }
> int ip_defrag(struct net *net, struct sk_buff *skb, u32 user);
> +
> +#ifdef CONFIG_DEBUG_INFO_BTF
> +int register_ip_frag_bpf(void);
> +#else
> +static inline int register_ip_frag_bpf(void)
> +{
> + return 0;
> +}
> +#endif
> +
> #ifdef CONFIG_INET
> struct sk_buff *ip_check_defrag(struct net *net, struct sk_buff *skb,
> u32 user);
> #else
> diff --git a/net/ipv4/Makefile b/net/ipv4/Makefile
> index 880277c9fd07..950efb166d37 100644
> --- a/net/ipv4/Makefile
> +++ b/net/ipv4/Makefile
> @@ -65,6 +65,7 @@ obj-$(CONFIG_TCP_CONG_ILLINOIS) += tcp_illinois.o
> obj-$(CONFIG_NET_SOCK_MSG) += tcp_bpf.o
> obj-$(CONFIG_BPF_SYSCALL) += udp_bpf.o
> obj-$(CONFIG_NETLABEL) += cipso_ipv4.o
> +obj-$(CONFIG_DEBUG_INFO_BTF) += ip_fragment_bpf.o
> obj-$(CONFIG_XFRM) += xfrm4_policy.o xfrm4_state.o xfrm4_input.o \
> xfrm4_output.o xfrm4_protocol.o
> diff --git a/net/ipv4/ip_fragment.c b/net/ipv4/ip_fragment.c
> index 959d2c4260ea..e3fda5203f09 100644
> --- a/net/ipv4/ip_fragment.c
> +++ b/net/ipv4/ip_fragment.c
> @@ -759,5 +759,7 @@ void __init ipfrag_init(void)
> if (inet_frags_init(&ip4_frags))
> panic("IP: failed to allocate ip4_frags cache\n");
> ip4_frags_ctl_register();
> + if (register_ip_frag_bpf())
> + panic("IP: bpf: failed to register ip_frag_bpf\n");
> register_pernet_subsys(&ip4_frags_ops);
> }
> diff --git a/net/ipv4/ip_fragment_bpf.c b/net/ipv4/ip_fragment_bpf.c
> new file mode 100644
> index 000000000000..a9e5908ed216
> --- /dev/null
> +++ b/net/ipv4/ip_fragment_bpf.c
> @@ -0,0 +1,98 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/* Unstable ipv4 fragmentation helpers for TC-BPF hook
> + *
> + * These are called from SCHED_CLS BPF programs. Note that it is allowed
> to
> + * break compatibility for these functions since the interface they are
> exposed
> + * through to BPF programs is explicitly unstable.
> + */
> +
> +#include <linux/bpf.h>
> +#include <linux/btf_ids.h>
> +#include <linux/ip.h>
> +#include <linux/filter.h>
> +#include <linux/netdevice.h>
> +#include <net/ip.h>
> +#include <net/sock.h>
> +
> +__diag_push();
> +__diag_ignore_all("-Wmissing-prototypes",
> + "Global functions as their definitions will be in ip_fragment BTF");
> +
> +/* bpf_ip_check_defrag - Defragment an ipv4 packet
> + *
> + * This helper takes an skb as input. If this skb successfully
> reassembles
> + * the original packet, the skb is updated to contain the original,
> reassembled
> + * packet.
> + *
> + * Otherwise (on error or incomplete reassembly), the input skb remains
> + * unmodified.
> + *
> + * Parameters:
> + * @ctx - Pointer to program context (skb)
> + * @netns - Child network namespace id. If value is a negative signed
> + * 32-bit integer, the netns of the device in the skb is used.
> + *
> + * Return:
> + * 0 on successfully reassembly or non-fragmented packet. Negative value
> on
> + * error or incomplete reassembly.
> + */
> +int bpf_ip_check_defrag(struct __sk_buff *ctx, u64 netns)
Needs a __bpf_kfunc tag as well?
> +{
> + struct sk_buff *skb = (struct sk_buff *)ctx;
> + struct sk_buff *skb_cpy, *skb_out;
> + struct net *caller_net;
> + struct net *net;
> + int mac_len;
> + void *mac;
> +
[..]
> + if (unlikely(!((s32)netns < 0 || netns <= S32_MAX)))
> + return -EINVAL;
Can you explain what it does? Is it checking for -1 explicitly? Not sure
it works :-/
Maybe we can spell out the cases explicitly?
if (unlikely(
((s32)netns < 0 && netns != S32_MAX) || /* -1 */
netns > U32_MAX /* higher 4 bytes */
)
return -EINVAL;
> +
> + caller_net = skb->dev ? dev_net(skb->dev) : sock_net(skb->sk);
> + if ((s32)netns < 0) {
> + net = caller_net;
> + } else {
> + net = get_net_ns_by_id(caller_net, netns);
> + if (unlikely(!net))
> + return -EINVAL;
> + }
> +
> + mac_len = skb->mac_len;
> + skb_cpy = skb_copy(skb, GFP_ATOMIC);
> + if (!skb_cpy)
> + return -ENOMEM;
> +
> + skb_out = ip_check_defrag(net, skb_cpy, IP_DEFRAG_BPF);
> + if (IS_ERR(skb_out))
> + return PTR_ERR(skb_out);
> +
> + skb_morph(skb, skb_out);
> + kfree_skb(skb_out);
> +
> + /* ip_check_defrag() does not maintain mac header, so push empty header
> + * in so prog sees the correct layout. The empty mac header will be
> + * later pulled from cls_bpf.
> + */
> + mac = skb_push(skb, mac_len);
> + memset(mac, 0, mac_len);
> + bpf_compute_data_pointers(skb);
> +
> + return 0;
> +}
> +
> +__diag_pop()
> +
> +BTF_SET8_START(ip_frag_kfunc_set)
> +BTF_ID_FLAGS(func, bpf_ip_check_defrag, KF_CHANGES_PKT)
> +BTF_SET8_END(ip_frag_kfunc_set)
> +
> +static const struct btf_kfunc_id_set ip_frag_bpf_kfunc_set = {
> + .owner = THIS_MODULE,
> + .set = &ip_frag_kfunc_set,
> +};
> +
> +int register_ip_frag_bpf(void)
> +{
> + return register_btf_kfunc_id_set(BPF_PROG_TYPE_SCHED_CLS,
> + &ip_frag_bpf_kfunc_set);
> +}
> --
> 2.39.1
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