bpf: add bpf_link support for BPF_NETFILTER programs

Add bpf_link support skeleton.  To keep this reviewable, no bpf program
can be invoked yet, if a program is attached only a c-stub is called and
not the actual bpf program.

Defaults to 'y' if both netfilter and bpf syscall are enabled in kconfig.

Uapi example usage:
	union bpf_attr attr = { };

	attr.link_create.prog_fd = progfd;
	attr.link_create.attach_type = 0; /* unused */
	attr.link_create.netfilter.pf = PF_INET;
	attr.link_create.netfilter.hooknum = NF_INET_LOCAL_IN;
	attr.link_create.netfilter.priority = -128;

	err = bpf(BPF_LINK_CREATE, &attr, sizeof(attr));

... this would attach progfd to ipv4:input hook.

Such hook gets removed automatically if the calling program exits.

BPF_NETFILTER program invocation is added in followup change.

NF_HOOK_OP_BPF enum will eventually be read from nfnetlink_hook, it
allows to tell userspace which program is attached at the given hook
when user runs 'nft hook list' command rather than just the priority
and not-very-helpful 'this hook runs a bpf prog but I can't tell which
one'.

Will also be used to disallow registration of two bpf programs with
same priority in a followup patch.

v4: arm32 cmpxchg only supports 32bit operand
    s/prio/priority/
v3: restrict prog attachment to ip/ip6 for now, lets lift restrictions if
    more use cases pop up (arptables, ebtables, netdev ingress/egress etc).

Signed-off-by: Florian Westphal <fw@strlen.de>
Link: https://lore.kernel.org/r/20230421170300.24115-2-fw@strlen.de
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Florian Westphal 2023-04-21 19:02:54 +02:00 committed by Alexei Starovoitov
parent 45cea721ea
commit 84601d6ee6
7 changed files with 194 additions and 0 deletions

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@ -80,6 +80,7 @@ typedef unsigned int nf_hookfn(void *priv,
enum nf_hook_ops_type {
NF_HOOK_OP_UNDEFINED,
NF_HOOK_OP_NF_TABLES,
NF_HOOK_OP_BPF,
};
struct nf_hook_ops {

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@ -0,0 +1,10 @@
/* SPDX-License-Identifier: GPL-2.0 */
#if IS_ENABLED(CONFIG_NETFILTER_BPF_LINK)
int bpf_nf_link_attach(const union bpf_attr *attr, struct bpf_prog *prog);
#else
static inline int bpf_nf_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
{
return -EOPNOTSUPP;
}
#endif

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@ -986,6 +986,7 @@ enum bpf_prog_type {
BPF_PROG_TYPE_LSM,
BPF_PROG_TYPE_SK_LOOKUP,
BPF_PROG_TYPE_SYSCALL, /* a program that can execute syscalls */
BPF_PROG_TYPE_NETFILTER,
};
enum bpf_attach_type {
@ -1050,6 +1051,7 @@ enum bpf_link_type {
BPF_LINK_TYPE_PERF_EVENT = 7,
BPF_LINK_TYPE_KPROBE_MULTI = 8,
BPF_LINK_TYPE_STRUCT_OPS = 9,
BPF_LINK_TYPE_NETFILTER = 10,
MAX_BPF_LINK_TYPE,
};
@ -1560,6 +1562,12 @@ union bpf_attr {
*/
__u64 cookie;
} tracing;
struct {
__u32 pf;
__u32 hooknum;
__s32 priority;
__u32 flags;
} netfilter;
};
} link_create;
@ -6410,6 +6418,12 @@ struct bpf_link_info {
struct {
__u32 map_id;
} struct_ops;
struct {
__u32 pf;
__u32 hooknum;
__s32 priority;
__u32 flags;
} netfilter;
};
} __attribute__((aligned(8)));

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@ -35,6 +35,7 @@
#include <linux/rcupdate_trace.h>
#include <linux/memcontrol.h>
#include <linux/trace_events.h>
#include <net/netfilter/nf_bpf_link.h>
#define IS_FD_ARRAY(map) ((map)->map_type == BPF_MAP_TYPE_PERF_EVENT_ARRAY || \
(map)->map_type == BPF_MAP_TYPE_CGROUP_ARRAY || \
@ -2462,6 +2463,7 @@ static bool is_net_admin_prog_type(enum bpf_prog_type prog_type)
case BPF_PROG_TYPE_CGROUP_SYSCTL:
case BPF_PROG_TYPE_SOCK_OPS:
case BPF_PROG_TYPE_EXT: /* extends any prog */
case BPF_PROG_TYPE_NETFILTER:
return true;
case BPF_PROG_TYPE_CGROUP_SKB:
/* always unpriv */
@ -4588,6 +4590,7 @@ static int link_create(union bpf_attr *attr, bpfptr_t uattr)
switch (prog->type) {
case BPF_PROG_TYPE_EXT:
case BPF_PROG_TYPE_NETFILTER:
break;
case BPF_PROG_TYPE_PERF_EVENT:
case BPF_PROG_TYPE_TRACEPOINT:
@ -4654,6 +4657,9 @@ static int link_create(union bpf_attr *attr, bpfptr_t uattr)
case BPF_PROG_TYPE_XDP:
ret = bpf_xdp_link_attach(attr, prog);
break;
case BPF_PROG_TYPE_NETFILTER:
ret = bpf_nf_link_attach(attr, prog);
break;
#endif
case BPF_PROG_TYPE_PERF_EVENT:
case BPF_PROG_TYPE_TRACEPOINT:

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@ -30,6 +30,9 @@ config NETFILTER_FAMILY_BRIDGE
config NETFILTER_FAMILY_ARP
bool
config NETFILTER_BPF_LINK
def_bool BPF_SYSCALL
config NETFILTER_NETLINK_HOOK
tristate "Netfilter base hook dump support"
depends on NETFILTER_ADVANCED

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@ -22,6 +22,7 @@ nf_conntrack-$(CONFIG_DEBUG_INFO_BTF) += nf_conntrack_bpf.o
endif
obj-$(CONFIG_NETFILTER) = netfilter.o
obj-$(CONFIG_NETFILTER_BPF_LINK) += nf_bpf_link.o
obj-$(CONFIG_NETFILTER_NETLINK) += nfnetlink.o
obj-$(CONFIG_NETFILTER_NETLINK_ACCT) += nfnetlink_acct.o

159
net/netfilter/nf_bpf_link.c Normal file
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@ -0,0 +1,159 @@
// SPDX-License-Identifier: GPL-2.0
#include <linux/bpf.h>
#include <linux/netfilter.h>
#include <net/netfilter/nf_bpf_link.h>
#include <uapi/linux/netfilter_ipv4.h>
static unsigned int nf_hook_run_bpf(void *bpf_prog, struct sk_buff *skb,
const struct nf_hook_state *s)
{
return NF_ACCEPT;
}
struct bpf_nf_link {
struct bpf_link link;
struct nf_hook_ops hook_ops;
struct net *net;
u32 dead;
};
static void bpf_nf_link_release(struct bpf_link *link)
{
struct bpf_nf_link *nf_link = container_of(link, struct bpf_nf_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))
nf_unregister_net_hook(nf_link->net, &nf_link->hook_ops);
}
static void bpf_nf_link_dealloc(struct bpf_link *link)
{
struct bpf_nf_link *nf_link = container_of(link, struct bpf_nf_link, link);
kfree(nf_link);
}
static int bpf_nf_link_detach(struct bpf_link *link)
{
bpf_nf_link_release(link);
return 0;
}
static void bpf_nf_link_show_info(const struct bpf_link *link,
struct seq_file *seq)
{
struct bpf_nf_link *nf_link = container_of(link, struct bpf_nf_link, link);
seq_printf(seq, "pf:\t%u\thooknum:\t%u\tprio:\t%d\n",
nf_link->hook_ops.pf, nf_link->hook_ops.hooknum,
nf_link->hook_ops.priority);
}
static int bpf_nf_link_fill_link_info(const struct bpf_link *link,
struct bpf_link_info *info)
{
struct bpf_nf_link *nf_link = container_of(link, struct bpf_nf_link, link);
info->netfilter.pf = nf_link->hook_ops.pf;
info->netfilter.hooknum = nf_link->hook_ops.hooknum;
info->netfilter.priority = nf_link->hook_ops.priority;
info->netfilter.flags = 0;
return 0;
}
static int bpf_nf_link_update(struct bpf_link *link, struct bpf_prog *new_prog,
struct bpf_prog *old_prog)
{
return -EOPNOTSUPP;
}
static const struct bpf_link_ops bpf_nf_link_lops = {
.release = bpf_nf_link_release,
.dealloc = bpf_nf_link_dealloc,
.detach = bpf_nf_link_detach,
.show_fdinfo = bpf_nf_link_show_info,
.fill_link_info = bpf_nf_link_fill_link_info,
.update_prog = bpf_nf_link_update,
};
static int bpf_nf_check_pf_and_hooks(const union bpf_attr *attr)
{
switch (attr->link_create.netfilter.pf) {
case NFPROTO_IPV4:
case NFPROTO_IPV6:
if (attr->link_create.netfilter.hooknum >= NF_INET_NUMHOOKS)
return -EPROTO;
break;
default:
return -EAFNOSUPPORT;
}
if (attr->link_create.netfilter.flags)
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 */
}
return 0;
}
int bpf_nf_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
{
struct net *net = current->nsproxy->net_ns;
struct bpf_link_primer link_primer;
struct bpf_nf_link *link;
int err;
if (attr->link_create.flags)
return -EINVAL;
err = bpf_nf_check_pf_and_hooks(attr);
if (err)
return err;
link = kzalloc(sizeof(*link), GFP_USER);
if (!link)
return -ENOMEM;
bpf_link_init(&link->link, BPF_LINK_TYPE_NETFILTER, &bpf_nf_link_lops, prog);
link->hook_ops.hook = nf_hook_run_bpf;
link->hook_ops.hook_ops_type = NF_HOOK_OP_BPF;
link->hook_ops.priv = prog;
link->hook_ops.pf = attr->link_create.netfilter.pf;
link->hook_ops.priority = attr->link_create.netfilter.priority;
link->hook_ops.hooknum = attr->link_create.netfilter.hooknum;
link->net = net;
link->dead = false;
err = bpf_link_prime(&link->link, &link_primer);
if (err) {
kfree(link);
return err;
}
err = nf_register_net_hook(net, &link->hook_ops);
if (err) {
bpf_link_cleanup(&link_primer);
return err;
}
return bpf_link_settle(&link_primer);
}