[PATCH bpf-next 1/7] tools: libbpf: add netfilter link attach helper

Daniel Xu
2023-06-26T23:02:35Z

Add new api function: bpf_program__attach_netfilter.

It takes a bpf program (netfilter type), and a pointer to a option struct
that contains the desired attachment (protocol family, priority, hook
location, ...).

It returns a pointer to a 'bpf_link' structure or NULL on error.

Next patch adds new netfilter_basic test that uses this function to
attach a program to a few pf/hook/priority combinations.

Co-developed-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Florian Westphal <fw@strlen.de>
Suggested-by: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Signed-off-by: Daniel Xu <dxu@dxuuu.xyz>
---
tools/lib/bpf/bpf.c | 8 +++++++
tools/lib/bpf/bpf.h | 6 +++++
tools/lib/bpf/libbpf.c | 47 ++++++++++++++++++++++++++++++++++++++++
tools/lib/bpf/libbpf.h | 15 +++++++++++++
tools/lib/bpf/libbpf.map | 1 +
5 files changed, 77 insertions(+)

diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
index ed86b37d8024..3b0da19715e1 100644
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c
@@ -741,6 +741,14 @@ int bpf_link_create(int prog_fd, int target_fd,
if (!OPTS_ZEROED(opts, tracing))
return libbpf_err(-EINVAL);
break;
+ case BPF_NETFILTER:
+ attr.link_create.netfilter.pf = OPTS_GET(opts, netfilter.pf, 0);
+ attr.link_create.netfilter.hooknum = OPTS_GET(opts, netfilter.hooknum, 0);
+ attr.link_create.netfilter.priority = OPTS_GET(opts, netfilter.priority, 0);
+ attr.link_create.netfilter.flags = OPTS_GET(opts, netfilter.flags, 0);
+ if (!OPTS_ZEROED(opts, netfilter))
+ return libbpf_err(-EINVAL);
+ break;
default:
if (!OPTS_ZEROED(opts, flags))
return libbpf_err(-EINVAL);
diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
index 9aa0ee473754..c676295ab9bf 100644
--- a/tools/lib/bpf/bpf.h
+++ b/tools/lib/bpf/bpf.h
@@ -349,6 +349,12 @@ struct bpf_link_create_opts {
struct {
__u64 cookie;
} tracing;
+ struct {
+ __u32 pf;
+ __u32 hooknum;
+ __s32 priority;
+ __u32 flags;
+ } netfilter;
};
size_t :0;
};
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 214f828ece6b..a8b9d5abb55f 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -11811,6 +11811,53 @@ static int attach_iter(const struct bpf_program *prog, long cookie, struct bpf_l
return libbpf_get_error(*link);
}

+struct bpf_link *bpf_program__attach_netfilter(const struct bpf_program *prog,
+ const struct bpf_netfilter_opts *opts)
+{
+ DECLARE_LIBBPF_OPTS(bpf_link_create_opts, link_create_opts);
+ struct bpf_link *link;
+ int prog_fd, link_fd;
+
+ if (!OPTS_VALID(opts, bpf_netfilter_opts))
+ return libbpf_err_ptr(-EINVAL);
+
+ link_create_opts.netfilter.pf = OPTS_GET(opts, pf, 0);
+ link_create_opts.netfilter.hooknum = OPTS_GET(opts, hooknum, 0);
+ link_create_opts.netfilter.priority = OPTS_GET(opts, priority, 0);
+ link_create_opts.netfilter.flags = OPTS_GET(opts, flags, 0);
+
+ prog_fd = bpf_program__fd(prog);
+ if (prog_fd < 0) {
+ pr_warn("prog '%s': can't attach before loaded\n", prog->name);
+ return libbpf_err_ptr(-EINVAL);
+ }
+
+ link = calloc(1, sizeof(*link));
+ if (!link)
+ return libbpf_err_ptr(-ENOMEM);
+ link->detach = &bpf_link__detach_fd;
+
+ link_fd = bpf_link_create(prog_fd, 0, BPF_NETFILTER, &link_create_opts);
+
+ link->fd = ensure_good_fd(link_fd);
+
+ if (link->fd < 0) {
+ char errmsg[STRERR_BUFSIZE];
+
+ link_fd = -errno;
+ free(link);
+ pr_warn("prog '%s': failed to attach to pf:%d,hooknum:%d:prio:%d: %s\n",
+ prog->name,
+ OPTS_GET(opts, pf, 0),
+ OPTS_GET(opts, hooknum, 0),
+ OPTS_GET(opts, priority, 0),
+ libbpf_strerror_r(link_fd, errmsg, sizeof(errmsg)));
+ return libbpf_err_ptr(link_fd);
+ }
+
+ return link;
+}
+
struct bpf_link *bpf_program__attach(const struct bpf_program *prog)
{
struct bpf_link *link = NULL;
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index 754da73c643b..10642ad69d76 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -718,6 +718,21 @@ LIBBPF_API struct bpf_link *
bpf_program__attach_freplace(const struct bpf_program *prog,
int target_fd, const char *attach_func_name);

+struct bpf_netfilter_opts {
+ /* size of this struct, for forward/backward compatibility */
+ size_t sz;
+
+ __u32 pf;
+ __u32 hooknum;
+ __s32 priority;
+ __u32 flags;
+};
+#define bpf_netfilter_opts__last_field flags
+
+LIBBPF_API struct bpf_link *
+bpf_program__attach_netfilter(const struct bpf_program *prog,
+ const struct bpf_netfilter_opts *opts);
+
struct bpf_map;

LIBBPF_API struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map);
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index 7521a2fb7626..d9ec4407befa 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -395,4 +395,5 @@ LIBBPF_1.2.0 {
LIBBPF_1.3.0 {
global:
bpf_obj_pin_opts;
+ bpf_program__attach_netfilter;
} LIBBPF_1.2.0;
--
2.40.1