Merge branch 'Link-based-attach-to-netns'

Jakub Sitnicki says:

====================
One of the pieces of feedback from recent review of BPF hooks for socket
lookup [0] was that new program types should use bpf_link-based
attachment.

This series introduces new bpf_link type for attaching to network
namespace. All link operations are supported. Errors returned from ops
follow cgroup example. Patch 4 description goes into error semantics.

The major change in v2 is a switch away from RCU to mutex-only
synchronization. Andrii pointed out that it is not needed, and it makes
sense to keep locking straightforward.

Also, there were a couple of bugs in update_prog and fill_info initial
implementation, one picked up by kbuild. Those are now fixed. Tests have
been extended to cover them. Full changelog below.

Series is organized as so:

Patches 1-3 prepare a space in struct net to keep state for attached BPF
programs, and massage the code in flow_dissector to make it attach type
agnostic, to finally move it under kernel/bpf/.

Patch 4, the most important one, introduces new bpf_link link type for
attaching to network namespace.

Patch 5 unifies the update error (ENOLINK) between BPF cgroup and netns.

Patches 6-8 make libbpf and bpftool aware of the new link type.

Patches 9-12 Add and extend tests to check that link low- and high-level
API for operating on links to netns works as intended.

Thanks to Alexei, Andrii, Lorenz, Marek, and Stanislav for feedback.

-jkbs

[0] https://lore.kernel.org/bpf/20200511185218.1422406-1-jakub@cloudflare.com/

Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: Lorenz Bauer <lmb@cloudflare.com>
Cc: Marek Majkowski <marek@cloudflare.com>
Cc: Stanislav Fomichev <sdf@google.com>

v1 -> v2:

- Switch to mutex-only synchronization. Don't rely on RCU grace period
  guarantee when accessing struct net from link release / update /
  fill_info, and when accessing bpf_link from pernet pre_exit
  callback. (Andrii)
- Drop patch 1, no longer needed with mutex-only synchronization.
- Don't leak uninitialized variable contents from fill_info callback
  when link is in defunct state. (kbuild)
- Make fill_info treat the link as defunct (i.e. no attached netns) when
  struct net refcount is 0, but link has not been yet auto-detached.
- Add missing BPF_LINK_TYPE define in bpf_types.h for new link type.
- Fix link update_prog callback to update the prog that will run, and
  not just the link itself.
- Return EEXIST on prog attach when link already exists, and on link
  create when prog is already attached directly. (Andrii)
- Return EINVAL on prog detach when link is attached. (Andrii)
- Fold __netns_bpf_link_attach into its only caller. (Stanislav)
- Get rid of a wrapper around container_of() (Andrii)
- Use rcu_dereference_protected instead of rcu_access_pointer on
  update-side. (Stanislav)
- Make return-on-success from netns_bpf_link_create less
  confusing. (Andrii)
- Adapt bpf_link for cgroup to return ENOLINK when updating a defunct
  link. (Andrii, Alexei)
- Order new exported symbols in libbpf.map alphabetically (Andrii)
- Keep libbpf's "failed to attach link" warning message clear as to what
  we failed to attach to (cgroup vs netns). (Andrii)
- Extract helpers for printing link attach type. (bpftool, Andrii)
- Switch flow_dissector tests to BPF skeleton and extend them to
  exercise link-based flow dissector attachment. (Andrii)
- Harden flow dissector attachment tests with prog query checks after
  prog attach/detach, or link create/update/close.
- Extend flow dissector tests to cover fill_info for defunct links.
- Rebase onto recent bpf-next
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 10 insertions, 10 deletions

diff --git a/tools/testing/selftests/bpf/progs/bpf_flow.c b/tools/testing/selftests/bpf/progs/bpf_flow.c
index 9941f0ba471e7..de6de92215180 100644
--- a/tools/testing/selftests/bpf/progs/bpf_flow.c
+++ b/tools/testing/selftests/bpf/progs/bpf_flow.c
@@ -20,20 +20,20 @@
 #include <bpf/bpf_endian.h>
 
 int _version SEC("version") = 1;
-#define PROG(F) SEC(#F) int bpf_func_##F
+#define PROG(F) PROG_(F, _##F)
+#define PROG_(NUM, NAME) SEC("flow_dissector/"#NUM) int bpf_func##NAME
 
 /* These are the identifiers of the BPF programs that will be used in tail
  * calls. Name is limited to 16 characters, with the terminating character and
  * bpf_func_ above, we have only 6 to work with, anything after will be cropped.
  */
-enum {
-	IP,
-	IPV6,
-	IPV6OP,	/* Destination/Hop-by-Hop Options IPv6 Extension header */
-	IPV6FR,	/* Fragmentation IPv6 Extension Header */
-	MPLS,
-	VLAN,
-};
+#define IP		0
+#define IPV6		1
+#define IPV6OP		2 /* Destination/Hop-by-Hop Options IPv6 Ext. Header */
+#define IPV6FR		3 /* Fragmentation IPv6 Extension Header */
+#define MPLS		4
+#define VLAN		5
+#define MAX_PROG	6
 
 #define IP_MF		0x2000
 #define IP_OFFSET	0x1FFF
@@ -59,7 +59,7 @@ struct frag_hdr {
 
 struct {
 	__uint(type, BPF_MAP_TYPE_PROG_ARRAY);
-	__uint(max_entries, 8);
+	__uint(max_entries, MAX_PROG);
 	__uint(key_size, sizeof(__u32));
 	__uint(value_size, sizeof(__u32));
 } jmp_table SEC(".maps");