From 91721c2d02d3a0141df8a4787c7079b89b0d0607 Mon Sep 17 00:00:00 2001 From: Daniel Xu Date: Fri, 21 Jul 2023 14:22:46 -0600 Subject: [PATCH] netfilter: bpf: Support BPF_F_NETFILTER_IP_DEFRAG in netfilter link This commit adds support for enabling IP defrag using pre-existing netfilter defrag support. Basically all the flag does is bump a refcnt while the link the active. Checks are also added to ensure the prog requesting defrag support is run _after_ netfilter defrag hooks. We also take care to avoid any issues w.r.t. module unloading -- while defrag is active on a link, the module is prevented from unloading. Signed-off-by: Daniel Xu Reviewed-by: Florian Westphal Link: https://lore.kernel.org/r/5cff26f97e55161b7d56b09ddcf5f8888a5add1d.1689970773.git.dxu@dxuuu.xyz Signed-off-by: Alexei Starovoitov --- include/uapi/linux/bpf.h | 5 ++ net/netfilter/nf_bpf_link.c | 123 +++++++++++++++++++++++++++++---- tools/include/uapi/linux/bpf.h | 5 ++ 3 files changed, 118 insertions(+), 15 deletions(-) diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index 14fd26b09e4b3..70da852006952 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -1188,6 +1188,11 @@ enum bpf_perf_event_type { */ #define BPF_F_KPROBE_MULTI_RETURN (1U << 0) +/* link_create.netfilter.flags used in LINK_CREATE command for + * BPF_PROG_TYPE_NETFILTER to enable IP packet defragmentation. + */ +#define BPF_F_NETFILTER_IP_DEFRAG (1U << 0) + /* When BPF ldimm64's insn[0].src_reg != 0 then this can have * the following extensions: * diff --git a/net/netfilter/nf_bpf_link.c b/net/netfilter/nf_bpf_link.c index c36da56d756f4..8fe594bbc7e24 100644 --- a/net/netfilter/nf_bpf_link.c +++ b/net/netfilter/nf_bpf_link.c @@ -1,6 +1,8 @@ // SPDX-License-Identifier: GPL-2.0 #include #include +#include +#include #include #include @@ -23,8 +25,88 @@ struct bpf_nf_link { struct nf_hook_ops hook_ops; struct net *net; u32 dead; + const struct nf_defrag_hook *defrag_hook; }; +static const struct nf_defrag_hook * +get_proto_defrag_hook(struct bpf_nf_link *link, + const struct nf_defrag_hook __rcu *global_hook, + const char *mod) +{ + const struct nf_defrag_hook *hook; + int err; + + /* RCU protects us from races against module unloading */ + rcu_read_lock(); + hook = rcu_dereference(global_hook); + if (!hook) { + rcu_read_unlock(); + err = request_module(mod); + if (err) + return ERR_PTR(err < 0 ? err : -EINVAL); + + rcu_read_lock(); + hook = rcu_dereference(global_hook); + } + + if (hook && try_module_get(hook->owner)) { + /* Once we have a refcnt on the module, we no longer need RCU */ + hook = rcu_pointer_handoff(hook); + } else { + WARN_ONCE(!hook, "%s has bad registration", mod); + hook = ERR_PTR(-ENOENT); + } + rcu_read_unlock(); + + if (!IS_ERR(hook)) { + err = hook->enable(link->net); + if (err) { + module_put(hook->owner); + hook = ERR_PTR(err); + } + } + + return hook; +} + +static int bpf_nf_enable_defrag(struct bpf_nf_link *link) +{ + const struct nf_defrag_hook __maybe_unused *hook; + + switch (link->hook_ops.pf) { +#if IS_ENABLED(CONFIG_NF_DEFRAG_IPV4) + case NFPROTO_IPV4: + hook = get_proto_defrag_hook(link, nf_defrag_v4_hook, "nf_defrag_ipv4"); + if (IS_ERR(hook)) + return PTR_ERR(hook); + + link->defrag_hook = hook; + return 0; +#endif +#if IS_ENABLED(CONFIG_NF_DEFRAG_IPV6) + case NFPROTO_IPV6: + hook = get_proto_defrag_hook(link, nf_defrag_v6_hook, "nf_defrag_ipv6"); + if (IS_ERR(hook)) + return PTR_ERR(hook); + + link->defrag_hook = hook; + return 0; +#endif + default: + return -EAFNOSUPPORT; + } +} + +static void bpf_nf_disable_defrag(struct bpf_nf_link *link) +{ + const struct nf_defrag_hook *hook = link->defrag_hook; + + if (!hook) + return; + hook->disable(link->net); + module_put(hook->owner); +} + static void bpf_nf_link_release(struct bpf_link *link) { struct bpf_nf_link *nf_link = container_of(link, struct bpf_nf_link, link); @@ -32,11 +114,11 @@ static void bpf_nf_link_release(struct bpf_link *link) if (nf_link->dead) return; - /* prevent hook-not-found warning splat from netfilter core when - * .detach was already called - */ - if (!cmpxchg(&nf_link->dead, 0, 1)) + /* do not double release in case .detach was already called */ + if (!cmpxchg(&nf_link->dead, 0, 1)) { nf_unregister_net_hook(nf_link->net, &nf_link->hook_ops); + bpf_nf_disable_defrag(nf_link); + } } static void bpf_nf_link_dealloc(struct bpf_link *link) @@ -92,6 +174,8 @@ static const struct bpf_link_ops bpf_nf_link_lops = { static int bpf_nf_check_pf_and_hooks(const union bpf_attr *attr) { + int prio; + switch (attr->link_create.netfilter.pf) { case NFPROTO_IPV4: case NFPROTO_IPV6: @@ -102,19 +186,18 @@ static int bpf_nf_check_pf_and_hooks(const union bpf_attr *attr) return -EAFNOSUPPORT; } - if (attr->link_create.netfilter.flags) + if (attr->link_create.netfilter.flags & ~BPF_F_NETFILTER_IP_DEFRAG) return -EOPNOTSUPP; - /* make sure conntrack confirm is always last. - * - * In the future, if userspace can e.g. request defrag, then - * "defrag_requested && prio before NF_IP_PRI_CONNTRACK_DEFRAG" - * should fail. - */ - switch (attr->link_create.netfilter.priority) { - case NF_IP_PRI_FIRST: return -ERANGE; /* sabotage_in and other warts */ - case NF_IP_PRI_LAST: return -ERANGE; /* e.g. conntrack confirm */ - } + /* make sure conntrack confirm is always last */ + prio = attr->link_create.netfilter.priority; + if (prio == NF_IP_PRI_FIRST) + return -ERANGE; /* sabotage_in and other warts */ + else if (prio == NF_IP_PRI_LAST) + return -ERANGE; /* e.g. conntrack confirm */ + else if ((attr->link_create.netfilter.flags & BPF_F_NETFILTER_IP_DEFRAG) && + prio <= NF_IP_PRI_CONNTRACK_DEFRAG) + return -ERANGE; /* cannot use defrag if prog runs before nf_defrag */ return 0; } @@ -149,6 +232,7 @@ int bpf_nf_link_attach(const union bpf_attr *attr, struct bpf_prog *prog) link->net = net; link->dead = false; + link->defrag_hook = NULL; err = bpf_link_prime(&link->link, &link_primer); if (err) { @@ -156,8 +240,17 @@ int bpf_nf_link_attach(const union bpf_attr *attr, struct bpf_prog *prog) return err; } + if (attr->link_create.netfilter.flags & BPF_F_NETFILTER_IP_DEFRAG) { + err = bpf_nf_enable_defrag(link); + if (err) { + bpf_link_cleanup(&link_primer); + return err; + } + } + err = nf_register_net_hook(net, &link->hook_ops); if (err) { + bpf_nf_disable_defrag(link); bpf_link_cleanup(&link_primer); return err; } diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h index 14fd26b09e4b3..70da852006952 100644 --- a/tools/include/uapi/linux/bpf.h +++ b/tools/include/uapi/linux/bpf.h @@ -1188,6 +1188,11 @@ enum bpf_perf_event_type { */ #define BPF_F_KPROBE_MULTI_RETURN (1U << 0) +/* link_create.netfilter.flags used in LINK_CREATE command for + * BPF_PROG_TYPE_NETFILTER to enable IP packet defragmentation. + */ +#define BPF_F_NETFILTER_IP_DEFRAG (1U << 0) + /* When BPF ldimm64's insn[0].src_reg != 0 then this can have * the following extensions: *