[PATCH RFC v2 bpf-next 1/3] bpf: add bpf_link support for BPF_NETFILTER programs

Florian Westphal
2023-03-02T17:28:21Z

Add bpf_link support skeleton. To keep this reviewable, no bpf program
can be invoked here, if a program would be attached only a c-stub is called.

This 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 = BPF_NETFILTER;
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'.

Signed-off-by: Florian Westphal <fw@strlen.de>
---
include/linux/netfilter.h | 1 +
include/net/netfilter/nf_hook_bpf.h | 2 +
include/uapi/linux/bpf.h | 12 +++
kernel/bpf/syscall.c | 6 ++
net/netfilter/Kconfig | 3 +
net/netfilter/Makefile | 1 +
net/netfilter/nf_bpf_link.c | 116 ++++++++++++++++++++++++++++
7 files changed, 141 insertions(+)
create mode 100644 include/net/netfilter/nf_hook_bpf.h
create mode 100644 net/netfilter/nf_bpf_link.c

diff --git a/include/linux/netfilter.h b/include/linux/netfilter.h
index 6863e271a9de..beec40ccbd79 100644
--- a/include/linux/netfilter.h
+++ b/include/linux/netfilter.h
@@ -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 {
diff --git a/include/net/netfilter/nf_hook_bpf.h b/include/net/netfilter/nf_hook_bpf.h
new file mode 100644
index 000000000000..9d1b338e89d7
--- /dev/null
+++ b/include/net/netfilter/nf_hook_bpf.h
@@ -0,0 +1,2 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+int bpf_nf_link_attach(const union bpf_attr *attr, struct bpf_prog *prog);
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index c9699304aed2..b063c6985769 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -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 {
@@ -1049,6 +1050,7 @@ 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,
};
@@ -1543,6 +1545,11 @@ union bpf_attr {
*/
__u64 cookie;
} tracing;
+ struct {
+ __u32 pf;
+ __u32 hooknum;
+ __s32 prio;
+ } netfilter;
};
} link_create;

@@ -6373,6 +6380,11 @@ struct bpf_link_info {
struct {
__u32 ifindex;
} xdp;
+ struct {
+ __u32 pf;
+ __u32 hooknum;
+ __s32 priority;
+ } netfilter;
};
} __attribute__((aligned(8)));

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index e3fcdc9836a6..8f5cd1fb83ee 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -35,6 +35,7 @@
#include <linux/rcupdate_trace.h>
#include <linux/memcontrol.h>
#include <linux/trace_events.h>
+#include <net/netfilter/nf_hook_bpf.h>

#define IS_FD_ARRAY(map) ((map)->map_type == BPF_MAP_TYPE_PERF_EVENT_ARRAY || \
(map)->map_type == BPF_MAP_TYPE_CGROUP_ARRAY || \
@@ -2448,6 +2449,7 @@ 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 */
@@ -4562,6 +4564,7 @@ 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:
@@ -4628,6 +4631,9 @@ 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:
diff --git a/net/netfilter/Kconfig b/net/netfilter/Kconfig
index 4d6737160857..bea06f62a30e 100644
--- a/net/netfilter/Kconfig
+++ b/net/netfilter/Kconfig
@@ -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
diff --git a/net/netfilter/Makefile b/net/netfilter/Makefile
index 5ffef1cd6143..d4958e7e7631 100644
--- a/net/netfilter/Makefile
+++ b/net/netfilter/Makefile
@@ -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
diff --git a/net/netfilter/nf_bpf_link.c b/net/netfilter/nf_bpf_link.c
new file mode 100644
index 000000000000..fa4fae5cc669
--- /dev/null
+++ b/net/netfilter/nf_bpf_link.c
@@ -0,0 +1,116 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/bpf.h>
+#include <linux/netfilter.h>
+
+#include <net/netfilter/nf_hook_bpf.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;
+};
+
+static void bpf_nf_link_release(struct bpf_link *link)
+{
+ struct bpf_nf_link *nf_link = container_of(link, struct bpf_nf_link, link);
+
+ 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;
+
+ 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,
+};
+
+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;
+
+ 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.prio;
+ link->hook_ops.hooknum = attr->link_create.netfilter.hooknum;
+
+ link->net = net;
+
+ err = bpf_link_prime(&link->link, &link_primer);
+ if (err)
+ goto out_free;
+
+ err = nf_register_net_hook(net, &link->hook_ops);
+ if (err) {
+ bpf_link_cleanup(&link_primer);
+ goto out_free;
+ }
+
+ return bpf_link_settle(&link_primer);
+
+out_free:
+ kfree(link);
+ return err;
+}
--
2.39.2