[PATCH bpf-next 05/10] bpf: Implement link detach for tc BPF link programs

[Daniel Borkmann <daniel@iogearbox.net>]

Add support for forced detach operation of tc BPF link. This detaches the link
but without destroying it. It has the same semantics as auto-detaching of BPF
link due to e.g. net device being destroyed for tc or XDP BPF link. Meaning,
in this case the BPF link is still a valid kernel object, but is defunct given
it is not attached anywhere anymore. It still holds a reference to the BPF
program, though. This functionality allows users with enough access rights to
manually force-detach attached tc BPF link without killing respective owner
process and to then introspect/debug the BPF assets. Similar LINK_DETACH exists
also for other BPF link types.

Co-developed-by: Nikolay Aleksandrov <razor@blackwall.org>
Signed-off-by: Nikolay Aleksandrov <razor@blackwall.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
---
 kernel/bpf/net.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/kernel/bpf/net.c b/kernel/bpf/net.c
index a74b86bb60a9..5650f62c1315 100644
--- a/kernel/bpf/net.c
+++ b/kernel/bpf/net.c
@@ -350,6 +350,12 @@ static void xtc_link_release(struct bpf_link *l)
 	rtnl_unlock();
 }
 
+static int xtc_link_detach(struct bpf_link *l)
+{
+	xtc_link_release(l);
+	return 0;
+}
+
 static void xtc_link_dealloc(struct bpf_link *l)
 {
 	struct bpf_tc_link *link = container_of(l, struct bpf_tc_link, link);
@@ -393,6 +399,7 @@ static int xtc_link_fill_info(const struct bpf_link *l,
 
 static const struct bpf_link_ops bpf_tc_link_lops = {
 	.release	= xtc_link_release,
+	.detach		= xtc_link_detach,
 	.dealloc	= xtc_link_dealloc,
 	.update_prog	= xtc_link_update,
 	.show_fdinfo	= xtc_link_fdinfo,
-- 
2.34.1