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2b99ef22e0
add glue code so a bpf program can be run using userspace-provided netfilter state and packet/skb. Default is to use ipv4:output hook point, but this can be overridden by userspace. Userspace provided netfilter state is restricted, only hook and protocol families can be overridden and only to ipv4/ipv6. Signed-off-by: Florian Westphal <fw@strlen.de> Link: https://lore.kernel.org/r/20230421170300.24115-7-fw@strlen.de Signed-off-by: Alexei Starovoitov <ast@kernel.org>
228 lines
5.4 KiB
C
228 lines
5.4 KiB
C
// SPDX-License-Identifier: GPL-2.0
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#include <linux/bpf.h>
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#include <linux/filter.h>
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#include <linux/netfilter.h>
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#include <net/netfilter/nf_bpf_link.h>
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#include <uapi/linux/netfilter_ipv4.h>
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static unsigned int nf_hook_run_bpf(void *bpf_prog, struct sk_buff *skb,
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const struct nf_hook_state *s)
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{
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const struct bpf_prog *prog = bpf_prog;
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struct bpf_nf_ctx ctx = {
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.state = s,
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.skb = skb,
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};
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return bpf_prog_run(prog, &ctx);
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}
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struct bpf_nf_link {
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struct bpf_link link;
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struct nf_hook_ops hook_ops;
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struct net *net;
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u32 dead;
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};
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static void bpf_nf_link_release(struct bpf_link *link)
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{
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struct bpf_nf_link *nf_link = container_of(link, struct bpf_nf_link, link);
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if (nf_link->dead)
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return;
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/* prevent hook-not-found warning splat from netfilter core when
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* .detach was already called
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*/
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if (!cmpxchg(&nf_link->dead, 0, 1))
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nf_unregister_net_hook(nf_link->net, &nf_link->hook_ops);
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}
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static void bpf_nf_link_dealloc(struct bpf_link *link)
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{
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struct bpf_nf_link *nf_link = container_of(link, struct bpf_nf_link, link);
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kfree(nf_link);
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}
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static int bpf_nf_link_detach(struct bpf_link *link)
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{
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bpf_nf_link_release(link);
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return 0;
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}
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static void bpf_nf_link_show_info(const struct bpf_link *link,
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struct seq_file *seq)
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{
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struct bpf_nf_link *nf_link = container_of(link, struct bpf_nf_link, link);
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seq_printf(seq, "pf:\t%u\thooknum:\t%u\tprio:\t%d\n",
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nf_link->hook_ops.pf, nf_link->hook_ops.hooknum,
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nf_link->hook_ops.priority);
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}
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static int bpf_nf_link_fill_link_info(const struct bpf_link *link,
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struct bpf_link_info *info)
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{
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struct bpf_nf_link *nf_link = container_of(link, struct bpf_nf_link, link);
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info->netfilter.pf = nf_link->hook_ops.pf;
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info->netfilter.hooknum = nf_link->hook_ops.hooknum;
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info->netfilter.priority = nf_link->hook_ops.priority;
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info->netfilter.flags = 0;
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return 0;
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}
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static int bpf_nf_link_update(struct bpf_link *link, struct bpf_prog *new_prog,
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struct bpf_prog *old_prog)
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{
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return -EOPNOTSUPP;
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}
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static const struct bpf_link_ops bpf_nf_link_lops = {
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.release = bpf_nf_link_release,
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.dealloc = bpf_nf_link_dealloc,
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.detach = bpf_nf_link_detach,
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.show_fdinfo = bpf_nf_link_show_info,
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.fill_link_info = bpf_nf_link_fill_link_info,
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.update_prog = bpf_nf_link_update,
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};
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static int bpf_nf_check_pf_and_hooks(const union bpf_attr *attr)
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{
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switch (attr->link_create.netfilter.pf) {
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case NFPROTO_IPV4:
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case NFPROTO_IPV6:
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if (attr->link_create.netfilter.hooknum >= NF_INET_NUMHOOKS)
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return -EPROTO;
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break;
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default:
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return -EAFNOSUPPORT;
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}
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if (attr->link_create.netfilter.flags)
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return -EOPNOTSUPP;
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/* make sure conntrack confirm is always last.
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*
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* In the future, if userspace can e.g. request defrag, then
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* "defrag_requested && prio before NF_IP_PRI_CONNTRACK_DEFRAG"
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* should fail.
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*/
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switch (attr->link_create.netfilter.priority) {
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case NF_IP_PRI_FIRST: return -ERANGE; /* sabotage_in and other warts */
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case NF_IP_PRI_LAST: return -ERANGE; /* e.g. conntrack confirm */
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}
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return 0;
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}
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int bpf_nf_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
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{
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struct net *net = current->nsproxy->net_ns;
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struct bpf_link_primer link_primer;
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struct bpf_nf_link *link;
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int err;
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if (attr->link_create.flags)
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return -EINVAL;
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err = bpf_nf_check_pf_and_hooks(attr);
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if (err)
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return err;
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link = kzalloc(sizeof(*link), GFP_USER);
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if (!link)
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return -ENOMEM;
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bpf_link_init(&link->link, BPF_LINK_TYPE_NETFILTER, &bpf_nf_link_lops, prog);
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link->hook_ops.hook = nf_hook_run_bpf;
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link->hook_ops.hook_ops_type = NF_HOOK_OP_BPF;
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link->hook_ops.priv = prog;
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link->hook_ops.pf = attr->link_create.netfilter.pf;
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link->hook_ops.priority = attr->link_create.netfilter.priority;
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link->hook_ops.hooknum = attr->link_create.netfilter.hooknum;
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link->net = net;
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link->dead = false;
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err = bpf_link_prime(&link->link, &link_primer);
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if (err) {
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kfree(link);
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return err;
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}
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err = nf_register_net_hook(net, &link->hook_ops);
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if (err) {
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bpf_link_cleanup(&link_primer);
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return err;
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}
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return bpf_link_settle(&link_primer);
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}
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const struct bpf_prog_ops netfilter_prog_ops = {
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.test_run = bpf_prog_test_run_nf,
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};
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static bool nf_ptr_to_btf_id(struct bpf_insn_access_aux *info, const char *name)
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{
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struct btf *btf;
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s32 type_id;
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btf = bpf_get_btf_vmlinux();
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if (IS_ERR_OR_NULL(btf))
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return false;
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type_id = btf_find_by_name_kind(btf, name, BTF_KIND_STRUCT);
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if (WARN_ON_ONCE(type_id < 0))
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return false;
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info->btf = btf;
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info->btf_id = type_id;
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info->reg_type = PTR_TO_BTF_ID | PTR_TRUSTED;
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return true;
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}
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static bool nf_is_valid_access(int off, int size, enum bpf_access_type type,
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const struct bpf_prog *prog,
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struct bpf_insn_access_aux *info)
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{
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if (off < 0 || off >= sizeof(struct bpf_nf_ctx))
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return false;
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if (type == BPF_WRITE)
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return false;
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switch (off) {
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case bpf_ctx_range(struct bpf_nf_ctx, skb):
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if (size != sizeof_field(struct bpf_nf_ctx, skb))
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return false;
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return nf_ptr_to_btf_id(info, "sk_buff");
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case bpf_ctx_range(struct bpf_nf_ctx, state):
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if (size != sizeof_field(struct bpf_nf_ctx, state))
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return false;
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return nf_ptr_to_btf_id(info, "nf_hook_state");
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default:
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return false;
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}
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return false;
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}
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static const struct bpf_func_proto *
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bpf_nf_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
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{
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return bpf_base_func_proto(func_id);
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}
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const struct bpf_verifier_ops netfilter_verifier_ops = {
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.is_valid_access = nf_is_valid_access,
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.get_func_proto = bpf_nf_func_proto,
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};
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