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Message-ID: <CAP01T76razfX1e7BsMbbyecPF+RjtJYoZifR-Um_BAoyPNOyKg@mail.gmail.com>
Date: Wed, 15 May 2024 23:59:25 +0200
From: Kumar Kartikeya Dwivedi <memxor@...il.com>
To: Lorenzo Bianconi <lorenzo@...nel.org>
Cc: bpf@...r.kernel.org, pablo@...filter.org, kadlec@...filter.org,
davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
netfilter-devel@...r.kernel.org, netdev@...r.kernel.org, ast@...nel.org,
daniel@...earbox.net, andrii@...nel.org, lorenzo.bianconi@...hat.com,
toke@...hat.com, fw@...len.de, hawk@...nel.org, horms@...nel.org,
donhunte@...hat.com
Subject: Re: [PATCH bpf-next 2/4] netfilter: add bpf_xdp_flow_offload_lookup kfunc
On Wed, 15 May 2024 at 23:13, Lorenzo Bianconi <lorenzo@...nel.org> wrote:
>
> Introduce bpf_xdp_flow_offload_lookup kfunc in order to perform the
> lookup of a given flowtable entry based on a fib tuple of incoming
> traffic.
> bpf_xdp_flow_offload_lookup can be used as building block to offload
> in xdp the processing of sw flowtable when hw flowtable is not
> available.
>
> Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.org>
> ---
> include/net/netfilter/nf_flow_table.h | 10 +++
> net/netfilter/Makefile | 5 ++
> net/netfilter/nf_flow_table_bpf.c | 95 +++++++++++++++++++++++++++
> net/netfilter/nf_flow_table_inet.c | 2 +
> 4 files changed, 112 insertions(+)
> create mode 100644 net/netfilter/nf_flow_table_bpf.c
>
> diff --git a/include/net/netfilter/nf_flow_table.h b/include/net/netfilter/nf_flow_table.h
> index 0bbe6ea8e0651..085660cbcd3f2 100644
> --- a/include/net/netfilter/nf_flow_table.h
> +++ b/include/net/netfilter/nf_flow_table.h
> @@ -312,6 +312,16 @@ unsigned int nf_flow_offload_ip_hook(void *priv, struct sk_buff *skb,
> unsigned int nf_flow_offload_ipv6_hook(void *priv, struct sk_buff *skb,
> const struct nf_hook_state *state);
>
> +#if (IS_BUILTIN(CONFIG_NF_FLOW_TABLE) && IS_ENABLED(CONFIG_DEBUG_INFO_BTF)) || \
> + (IS_MODULE(CONFIG_NF_FLOW_TABLE) && IS_ENABLED(CONFIG_DEBUG_INFO_BTF_MODULES))
> +extern int nf_flow_offload_register_bpf(void);
> +#else
> +static inline int nf_flow_offload_register_bpf(void)
> +{
> + return 0;
> +}
> +#endif
> +
> #define MODULE_ALIAS_NF_FLOWTABLE(family) \
> MODULE_ALIAS("nf-flowtable-" __stringify(family))
>
> diff --git a/net/netfilter/Makefile b/net/netfilter/Makefile
> index 614815a3ed738..18b09cec92024 100644
> --- a/net/netfilter/Makefile
> +++ b/net/netfilter/Makefile
> @@ -144,6 +144,11 @@ obj-$(CONFIG_NF_FLOW_TABLE) += nf_flow_table.o
> nf_flow_table-objs := nf_flow_table_core.o nf_flow_table_ip.o \
> nf_flow_table_offload.o
> nf_flow_table-$(CONFIG_NF_FLOW_TABLE_PROCFS) += nf_flow_table_procfs.o
> +ifeq ($(CONFIG_NF_FLOW_TABLE),m)
> +nf_flow_table-$(CONFIG_DEBUG_INFO_BTF_MODULES) += nf_flow_table_bpf.o
> +else ifeq ($(CONFIG_NF_FLOW_TABLE),y)
> +nf_flow_table-$(CONFIG_DEBUG_INFO_BTF) += nf_flow_table_bpf.o
> +endif
>
> obj-$(CONFIG_NF_FLOW_TABLE_INET) += nf_flow_table_inet.o
>
> diff --git a/net/netfilter/nf_flow_table_bpf.c b/net/netfilter/nf_flow_table_bpf.c
> new file mode 100644
> index 0000000000000..836a1127e4052
> --- /dev/null
> +++ b/net/netfilter/nf_flow_table_bpf.c
> @@ -0,0 +1,95 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/* Unstable Flow Table Helpers for XDP hook
> + *
> + * These are called from the XDP 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/kernel.h>
> +#include <linux/init.h>
> +#include <linux/module.h>
> +#include <net/netfilter/nf_flow_table.h>
> +#include <linux/bpf.h>
> +#include <linux/btf.h>
> +#include <net/xdp.h>
> +
> +__diag_push();
> +__diag_ignore_all("-Wmissing-prototypes",
> + "Global functions as their definitions will be in nf_flow_table BTF");
> +
> +static struct flow_offload_tuple_rhash *
> +bpf_xdp_flow_offload_tuple_lookup(struct net_device *dev,
> + struct flow_offload_tuple *tuple,
> + __be16 proto)
> +{
> + struct flow_offload_tuple_rhash *tuplehash;
> + struct nf_flowtable *flow_table;
> + struct flow_offload *flow;
> +
> + flow_table = nf_flowtable_by_dev(dev);
> + if (!flow_table)
> + return ERR_PTR(-ENOENT);
> +
> + tuplehash = flow_offload_lookup(flow_table, tuple);
> + if (!tuplehash)
> + return ERR_PTR(-ENOENT);
This is fine to do, but the caller should catch it using IS_ERR_PTR
and return NULL.
BPF side cannot distinguish ERR_PTR from normal pointer, so this will
cause a bad deref in the program.
> +
> + flow = container_of(tuplehash, struct flow_offload,
> + tuplehash[tuplehash->tuple.dir]);
> + flow_offload_refresh(flow_table, flow, false);
> +
> + return tuplehash;
> +}
> +
> +__bpf_kfunc struct flow_offload_tuple_rhash *
> +bpf_xdp_flow_offload_lookup(struct xdp_md *ctx,
> + struct bpf_fib_lookup *fib_tuple,
> + u32 fib_tuple__sz)
Do you think the __sz has the intended effect? It only works when the
preceding parameter is a void *.
If you have a type like struct bpf_fib_lookup, I think it should work
fine without taking a size at all.
> +{
> + struct xdp_buff *xdp = (struct xdp_buff *)ctx;
> + struct flow_offload_tuple tuple = {
> + .iifidx = fib_tuple->ifindex,
> + .l3proto = fib_tuple->family,
> + .l4proto = fib_tuple->l4_protocol,
> + .src_port = fib_tuple->sport,
> + .dst_port = fib_tuple->dport,
> + };
> + __be16 proto;
> +
> + switch (fib_tuple->family) {
> + case AF_INET:
> + tuple.src_v4.s_addr = fib_tuple->ipv4_src;
> + tuple.dst_v4.s_addr = fib_tuple->ipv4_dst;
> + proto = htons(ETH_P_IP);
> + break;
> + case AF_INET6:
> + tuple.src_v6 = *(struct in6_addr *)&fib_tuple->ipv6_src;
> + tuple.dst_v6 = *(struct in6_addr *)&fib_tuple->ipv6_dst;
> + proto = htons(ETH_P_IPV6);
> + break;
> + default:
> + return ERR_PTR(-EINVAL);
Likewise. While you check IS_ERR_VALUE in selftest, direct dereference
will be allowed by verifier, which would crash the kernel.
It's better to do something like conntrack kfuncs, where they set
opts->error when returning NULL, allowing better debugging in case
lookup fails.
> + }
> +
> + return bpf_xdp_flow_offload_tuple_lookup(xdp->rxq->dev, &tuple, proto);
> +}
> +
> +__diag_pop()
> +
> +BTF_KFUNCS_START(nf_ft_kfunc_set)
> +BTF_ID_FLAGS(func, bpf_xdp_flow_offload_lookup)
> +BTF_KFUNCS_END(nf_ft_kfunc_set)
> +
> +static const struct btf_kfunc_id_set nf_flow_offload_kfunc_set = {
> + .owner = THIS_MODULE,
> + .set = &nf_ft_kfunc_set,
> +};
> +
> +int nf_flow_offload_register_bpf(void)
> +{
> + return register_btf_kfunc_id_set(BPF_PROG_TYPE_XDP,
> + &nf_flow_offload_kfunc_set);
> +}
We should probably also expose it to skb? We just need net_device, so
it can work with both XDP and TC progs.
That would be similar to how we expose conntrack kfuncs to both XDP
and TC progs.
> +EXPORT_SYMBOL_GPL(nf_flow_offload_register_bpf);
> diff --git a/net/netfilter/nf_flow_table_inet.c b/net/netfilter/nf_flow_table_inet.c
> index 6eef15648b7b0..b13587238eceb 100644
> --- a/net/netfilter/nf_flow_table_inet.c
> +++ b/net/netfilter/nf_flow_table_inet.c
> @@ -98,6 +98,8 @@ static int __init nf_flow_inet_module_init(void)
> nft_register_flowtable_type(&flowtable_ipv6);
> nft_register_flowtable_type(&flowtable_inet);
>
> + nf_flow_offload_register_bpf();
> +
Error checking needed here? Kfunc registration can fail.
> return 0;
> }
>
> --
> 2.45.0
>
>
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