[PATCH v5 0/6] Add eBPF hooks for cgroups

This is v5 of the patch set to allow eBPF programs for network
filtering and accounting to be attached to cgroups, so that they apply
to all sockets of all tasks placed in that cgroup. The logic also
allows to be extendeded for other cgroup based eBPF logic.

After chatting with Daniel Borkmann and Alexei off-list, we concluded
that __dev_queue_xmit() is the place where the egress hooks should live
when eBPF programs need access to the L2 bits of the skb.


Changes from v4:

* Plug an skb leak when dropping packets due to eBPF verdicts in
  __dev_queue_xmit(). Spotted by Daniel Borkmann.

* Check for sk_fullsock(sk) in __cgroup_bpf_run_filter() so we don't
  operate on timewait or request sockets. Suggested by Daniel Borkmann.

* Add missing @parent parameter in kerneldoc of __cgroup_bpf_update().
  Spotted by Rami Rosen.

* Include linux/jump_label.h from bpf-cgroup.h to fix a kbuild error.


Changes from v3:

* Dropped the _FILTER suffix from BPF_PROG_TYPE_CGROUP_SOCKET_FILTER,
  renamed BPF_ATTACH_TYPE_CGROUP_INET_{E,IN}GRESS to
  BPF_CGROUP_INET_{IN,E}GRESS and alias BPF_MAX_ATTACH_TYPE to
  __BPF_MAX_ATTACH_TYPE, as suggested by Daniel Borkmann.

* Dropped the attach_flags member from the anonymous struct for BPF
  attach operations in union bpf_attr. They can be added later on via
  CHECK_ATTR. Requested by Daniel Borkmann and Alexei.

* Release old_prog at the end of __cgroup_bpf_update rather that at
  the beginning to fix a race gap between program updates and their
  users. Spotted by Daniel Borkmann.

* Plugged an skb leak when dropping packets on the egress path.
  Spotted by Daniel Borkmann.

* Add cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org to the loop, as suggested by Rami Rosen.

* Some minor coding style adoptions not worth mentioning in particular.


Changes from v2:

* Fixed the RCU locking details Tejun pointed out.

* Assert bpf_attr.flags == 0 in BPF_PROG_DETACH syscall handler.


Changes from v1:

* Moved all bpf specific cgroup code into its own file, and stub
  out related functions for !CONFIG_CGROUP_BPF as static inline nops.
  This way, the call sites are not cluttered with #ifdef guards while
  the feature remains compile-time configurable.

* Implemented the new scheme proposed by Tejun. Per cgroup, store one
  set of pointers that are pinned to the cgroup, and one for the
  programs that are effective. When a program is attached or detached,
  the change is propagated to all the cgroup's descendants. If a
  subcgroup has its own pinned program, skip the whole subbranch in
  order to allow delegation models.

* The hookup for egress packets is now done from __dev_queue_xmit().

* A static key is now used in both the ingress and egress fast paths
  to keep performance penalties close to zero if the feature is
  not in use.

* Overall cleanup to make the accessors use the program arrays.
  This should make it much easier to add new program types, which
  will then automatically follow the pinned vs. effective logic.

* Fixed locking issues, as pointed out by Eric Dumazet and Alexei
  Starovoitov. Changes to the program array are now done with
  xchg() and are protected by cgroup_mutex.

* eBPF programs are now expected to return 1 to let the packet pass,
  not >= 0. Pointed out by Alexei.

* Operation is now limited to INET sockets, so local AF_UNIX sockets
  are not affected. The enum members are renamed accordingly. In case
  other socket families should be supported, this can be extended in
  the future.

* The sample program learned to support both ingress and egress, and
  can now optionally make the eBPF program drop packets by making it
  return 0.


As always, feedback is much appreciated.

Thanks,
Daniel


Daniel Mack (6):
  bpf: add new prog type for cgroup socket filtering
  cgroup: add support for eBPF programs
  bpf: add BPF_PROG_ATTACH and BPF_PROG_DETACH commands
  net: filter: run cgroup eBPF ingress programs
  net: core: run cgroup eBPF egress programs
  samples: bpf: add userspace example for attaching eBPF programs to
    cgroups

 include/linux/bpf-cgroup.h      |  71 +++++++++++++++++
 include/linux/cgroup-defs.h     |   4 +
 include/uapi/linux/bpf.h        |  17 ++++
 init/Kconfig                    |  12 +++
 kernel/bpf/Makefile             |   1 +
 kernel/bpf/cgroup.c             | 166 ++++++++++++++++++++++++++++++++++++++++
 kernel/bpf/syscall.c            |  81 ++++++++++++++++++++
 kernel/bpf/verifier.c           |   1 +
 kernel/cgroup.c                 |  18 +++++
 net/core/dev.c                  |   6 ++
 net/core/filter.c               |  10 +++
 samples/bpf/Makefile            |   2 +
 samples/bpf/libbpf.c            |  21 +++++
 samples/bpf/libbpf.h            |   3 +
 samples/bpf/test_cgrp2_attach.c | 147 +++++++++++++++++++++++++++++++++++
 15 files changed, 560 insertions(+)
 create mode 100644 include/linux/bpf-cgroup.h
 create mode 100644 kernel/bpf/cgroup.c
 create mode 100644 samples/bpf/test_cgrp2_attach.c

-- 
2.5.5

For now, this program type is equivalent to BPF_PROG_TYPE_SOCKET_FILTER in
terms of checks during the verification process. It may access the skb as
well.

Programs of this type will be attached to cgroups for network filtering
and accounting.

Signed-off-by: Daniel Mack <daniel@zonque.org>
---
 include/uapi/linux/bpf.h | 9 +++++++++
 kernel/bpf/verifier.c    | 1 +
 net/core/filter.c        | 6 ++++++
 3 files changed, 16 insertions(+)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index f896dfa..55f815e 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h

@@ -96,8 +96,17 @@ enum bpf_prog_type {
 	BPF_PROG_TYPE_TRACEPOINT,
 	BPF_PROG_TYPE_XDP,
 	BPF_PROG_TYPE_PERF_EVENT,
+	BPF_PROG_TYPE_CGROUP_SOCKET,
 };
 
+enum bpf_attach_type {
+	BPF_CGROUP_INET_INGRESS,
+	BPF_CGROUP_INET_EGRESS,
+	__MAX_BPF_ATTACH_TYPE
+};
+
+#define MAX_BPF_ATTACH_TYPE __MAX_BPF_ATTACH_TYPE
+
 #define BPF_PSEUDO_MAP_FD	1
 
 /* flags for BPF_MAP_UPDATE_ELEM command */

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 90493a6..d5d2875 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c

@@ -1830,6 +1830,7 @@ static bool may_access_skb(enum bpf_prog_type type)
 	case BPF_PROG_TYPE_SOCKET_FILTER:
 	case BPF_PROG_TYPE_SCHED_CLS:
 	case BPF_PROG_TYPE_SCHED_ACT:
+	case BPF_PROG_TYPE_CGROUP_SOCKET:
 		return true;
 	default:
 		return false;

diff --git a/net/core/filter.c b/net/core/filter.c
index a83766b..176b6f2 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c

@@ -2848,12 +2848,18 @@ static struct bpf_prog_type_list xdp_type __read_mostly = {
 	.type	= BPF_PROG_TYPE_XDP,
 };
 
+static struct bpf_prog_type_list cg_sk_type __read_mostly = {
+	.ops	= &sk_filter_ops,
+	.type	= BPF_PROG_TYPE_CGROUP_SOCKET,
+};
+
 static int __init register_sk_filter_ops(void)
 {
 	bpf_register_prog_type(&sk_filter_type);
 	bpf_register_prog_type(&sched_cls_type);
 	bpf_register_prog_type(&sched_act_type);
 	bpf_register_prog_type(&xdp_type);
+	bpf_register_prog_type(&cg_sk_type);
 
 	return 0;
 }

-- 
2.5.5

This patch adds two sets of eBPF program pointers to struct cgroup.
One for such that are directly pinned to a cgroup, and one for such
that are effective for it.

To illustrate the logic behind that, assume the following example
cgroup hierarchy.

  A - B - C
        \ D - E

If only B has a program attached, it will be effective for B, C, D
and E. If D then attaches a program itself, that will be effective for
both D and E, and the program in B will only affect B and C. Only one
program of a given type is effective for a cgroup.

Attaching and detaching programs will be done through the bpf(2)
syscall. For now, ingress and egress inet socket filtering are the
only supported use-cases.

Signed-off-by: Daniel Mack <daniel@zonque.org>
---
 include/linux/bpf-cgroup.h  |  71 +++++++++++++++++++
 include/linux/cgroup-defs.h |   4 ++
 init/Kconfig                |  12 ++++
 kernel/bpf/Makefile         |   1 +
 kernel/bpf/cgroup.c         | 166 ++++++++++++++++++++++++++++++++++++++++++++
 kernel/cgroup.c             |  18 +++++
 6 files changed, 272 insertions(+)
 create mode 100644 include/linux/bpf-cgroup.h
 create mode 100644 kernel/bpf/cgroup.c

diff --git a/include/linux/bpf-cgroup.h b/include/linux/bpf-cgroup.h
new file mode 100644
index 0000000..fc076de
--- /dev/null
+++ b/include/linux/bpf-cgroup.h

@@ -0,0 +1,71 @@
+#ifndef _BPF_CGROUP_H
+#define _BPF_CGROUP_H
+
+#include <linux/bpf.h>
+#include <linux/jump_label.h>
+#include <uapi/linux/bpf.h>
+
+struct sock;
+struct cgroup;
+struct sk_buff;
+
+#ifdef CONFIG_CGROUP_BPF
+
+extern struct static_key_false cgroup_bpf_enabled_key;
+#define cgroup_bpf_enabled static_branch_unlikely(&cgroup_bpf_enabled_key)
+
+struct cgroup_bpf {
+	/*
+	 * Store two sets of bpf_prog pointers, one for programs that are
+	 * pinned directly to this cgroup, and one for those that are effective
+	 * when this cgroup is accessed.
+	 */
+	struct bpf_prog *prog[MAX_BPF_ATTACH_TYPE];
+	struct bpf_prog *effective[MAX_BPF_ATTACH_TYPE];
+};
+
+void cgroup_bpf_put(struct cgroup *cgrp);
+void cgroup_bpf_inherit(struct cgroup *cgrp, struct cgroup *parent);
+
+void __cgroup_bpf_update(struct cgroup *cgrp,
+			 struct cgroup *parent,
+			 struct bpf_prog *prog,
+			 enum bpf_attach_type type);
+
+/* Wrapper for __cgroup_bpf_update() protected by cgroup_mutex */
+void cgroup_bpf_update(struct cgroup *cgrp,
+		       struct bpf_prog *prog,
+		       enum bpf_attach_type type);
+
+int __cgroup_bpf_run_filter(struct sock *sk,
+			    struct sk_buff *skb,
+			    enum bpf_attach_type type);
+
+/* Wrapper for __cgroup_bpf_run_filter() guarded by cgroup_bpf_enabled */
+static inline int cgroup_bpf_run_filter(struct sock *sk,
+					struct sk_buff *skb,
+					enum bpf_attach_type type)
+{
+	if (cgroup_bpf_enabled)
+		return __cgroup_bpf_run_filter(sk, skb, type);
+
+	return 0;
+}
+
+#else
+
+struct cgroup_bpf {};
+static inline void cgroup_bpf_put(struct cgroup *cgrp) {}
+static inline void cgroup_bpf_inherit(struct cgroup *cgrp,
+				      struct cgroup *parent) {}
+
+static inline int cgroup_bpf_run_filter(struct sock *sk,
+					struct sk_buff *skb,
+					enum bpf_attach_type type)
+{
+	return 0;
+}
+
+#endif /* CONFIG_CGROUP_BPF */
+
+#endif /* _BPF_CGROUP_H */

diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index 5b17de6..861b467 100644
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h

@@ -16,6 +16,7 @@
 #include <linux/percpu-refcount.h>
 #include <linux/percpu-rwsem.h>
 #include <linux/workqueue.h>
+#include <linux/bpf-cgroup.h>
 
 #ifdef CONFIG_CGROUPS
 

@@ -300,6 +301,9 @@ struct cgroup {
 	/* used to schedule release agent */
 	struct work_struct release_agent_work;
 
+	/* used to store eBPF programs */
+	struct cgroup_bpf bpf;
+
 	/* ids of the ancestors at each level including self */
 	int ancestor_ids[];
 };

diff --git a/init/Kconfig b/init/Kconfig
index cac3f09..71c71b0 100644
--- a/init/Kconfig
+++ b/init/Kconfig

@@ -1144,6 +1144,18 @@ config CGROUP_PERF
 
 	  Say N if unsure.
 
+config CGROUP_BPF
+	bool "Support for eBPF programs attached to cgroups"
+	depends on BPF_SYSCALL && SOCK_CGROUP_DATA
+	help
+	  Allow attaching eBPF programs to a cgroup using the bpf(2)
+	  syscall command BPF_PROG_ATTACH.
+
+	  In which context these programs are accessed depends on the type
+	  of attachment. For instance, programs that are attached using
+	  BPF_CGROUP_INET_INGRESS will be executed on the ingress path of
+	  inet sockets.
+
 config CGROUP_DEBUG
 	bool "Example controller"
 	default n

diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile
index eed911d..b22256b 100644
--- a/kernel/bpf/Makefile
+++ b/kernel/bpf/Makefile

@@ -5,3 +5,4 @@ obj-$(CONFIG_BPF_SYSCALL) += hashtab.o arraymap.o percpu_freelist.o
 ifeq ($(CONFIG_PERF_EVENTS),y)
 obj-$(CONFIG_BPF_SYSCALL) += stackmap.o
 endif
+obj-$(CONFIG_CGROUP_BPF) += cgroup.o

diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
new file mode 100644
index 0000000..21d168c
--- /dev/null
+++ b/kernel/bpf/cgroup.c

@@ -0,0 +1,166 @@
+/*
+ * Functions to manage eBPF programs attached to cgroups
+ *
+ * Copyright (c) 2016 Daniel Mack
+ *
+ * This file is subject to the terms and conditions of version 2 of the GNU
+ * General Public License.  See the file COPYING in the main directory of the
+ * Linux distribution for more details.
+ */
+
+#include <linux/kernel.h>
+#include <linux/atomic.h>
+#include <linux/cgroup.h>
+#include <linux/slab.h>
+#include <linux/bpf.h>
+#include <linux/bpf-cgroup.h>
+#include <net/sock.h>
+
+DEFINE_STATIC_KEY_FALSE(cgroup_bpf_enabled_key);
+EXPORT_SYMBOL(cgroup_bpf_enabled_key);
+
+/**
+ * cgroup_bpf_put() - put references of all bpf programs
+ * @cgrp: the cgroup to modify
+ */
+void cgroup_bpf_put(struct cgroup *cgrp)
+{
+	unsigned int type;
+
+	for (type = 0; type < ARRAY_SIZE(cgrp->bpf.prog); type++) {
+		struct bpf_prog *prog = cgrp->bpf.prog[type];
+
+		if (prog) {
+			bpf_prog_put(prog);
+			static_branch_dec(&cgroup_bpf_enabled_key);
+		}
+	}
+}
+
+/**
+ * cgroup_bpf_inherit() - inherit effective programs from parent
+ * @cgrp: the cgroup to modify
+ * @parent: the parent to inherit from
+ */
+void cgroup_bpf_inherit(struct cgroup *cgrp, struct cgroup *parent)
+{
+	unsigned int type;
+
+	for (type = 0; type < ARRAY_SIZE(cgrp->bpf.effective); type++) {
+		struct bpf_prog *e;
+
+		e = rcu_dereference_protected(parent->bpf.effective[type],
+					      lockdep_is_held(&cgroup_mutex));
+		rcu_assign_pointer(cgrp->bpf.effective[type], e);
+	}
+}
+
+/**
+ * __cgroup_bpf_update() - Update the pinned program of a cgroup, and
+ *                         propagate the change to descendants
+ * @cgrp: The cgroup which descendants to traverse
+ * @parent: The parent of @cgrp, or %NULL if @cgrp is the root
+ * @prog: A new program to pin
+ * @type: Type of pinning operation (ingress/egress)
+ *
+ * Each cgroup has a set of two pointers for bpf programs; one for eBPF
+ * programs it owns, and which is effective for execution.
+ *
+ * If @prog is %NULL, this function attaches a new program to the cgroup and
+ * releases the one that is currently attached, if any. @prog is then made
+ * the effective program of type @type in that cgroup.
+ *
+ * If @prog is %NULL, the currently attached program of type @type is released,
+ * and the effective program of the parent cgroup (if any) is inherited to
+ * @cgrp.
+ *
+ * Then, the descendants of @cgrp are walked and the effective program for
+ * each of them is set to the effective program of @cgrp unless the
+ * descendant has its own program attached, in which case the subbranch is
+ * skipped. This ensures that delegated subcgroups with own programs are left
+ * untouched.
+ *
+ * Must be called with cgroup_mutex held.
+ */
+void __cgroup_bpf_update(struct cgroup *cgrp,
+			 struct cgroup *parent,
+			 struct bpf_prog *prog,
+			 enum bpf_attach_type type)
+{
+	struct bpf_prog *old_prog, *effective;
+	struct cgroup_subsys_state *pos;
+
+	old_prog = xchg(cgrp->bpf.prog + type, prog);
+
+	effective = (!prog && parent) ?
+		rcu_dereference_protected(parent->bpf.effective[type],
+					  lockdep_is_held(&cgroup_mutex)) :
+		prog;
+
+	css_for_each_descendant_pre(pos, &cgrp->self) {
+		struct cgroup *desc = container_of(pos, struct cgroup, self);
+
+		/* skip the subtree if the descendant has its own program */
+		if (desc->bpf.prog[type] && desc != cgrp)
+			pos = css_rightmost_descendant(pos);
+		else
+			rcu_assign_pointer(desc->bpf.effective[type],
+					   effective);
+	}
+
+	if (prog)
+		static_branch_inc(&cgroup_bpf_enabled_key);
+
+	if (old_prog) {
+		bpf_prog_put(old_prog);
+		static_branch_dec(&cgroup_bpf_enabled_key);
+	}
+}
+
+/**
+ * __cgroup_bpf_run_filter() - Run a program for packet filtering
+ * @sk: The socken sending or receiving traffic
+ * @skb: The skb that is being sent or received
+ * @type: The type of program to be exectuted
+ *
+ * If no socket is passed, or the socket is not of type INET or INET6,
+ * this function does nothing and returns 0.
+ *
+ * The program type passed in via @type must be suitable for network
+ * filtering. No further check is performed to assert that.
+ *
+ * This function will return %-EPERM if any if an attached program was found
+ * and if it returned != 1 during execution. In all other cases, 0 is returned.
+ */
+int __cgroup_bpf_run_filter(struct sock *sk,
+			    struct sk_buff *skb,
+			    enum bpf_attach_type type)
+{
+	struct bpf_prog *prog;
+	struct cgroup *cgrp;
+	int ret = 0;
+
+	if (!sk || !sk_fullsock(sk))
+		return 0;
+
+	if (sk->sk_family != AF_INET &&
+	    sk->sk_family != AF_INET6)
+		return 0;
+
+	cgrp = sock_cgroup_ptr(&sk->sk_cgrp_data);
+
+	rcu_read_lock();
+
+	prog = rcu_dereference(cgrp->bpf.effective[type]);
+	if (prog) {
+		unsigned int offset = skb->data - skb_mac_header(skb);
+
+		__skb_push(skb, offset);
+		ret = bpf_prog_run_clear_cb(prog, skb) == 1 ? 0 : -EPERM;
+		__skb_pull(skb, offset);
+	}
+
+	rcu_read_unlock();
+
+	return ret;
+}

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index d1c51b7..57ade89 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c

@@ -5038,6 +5038,8 @@ static void css_release_work_fn(struct work_struct *work)
 		if (cgrp->kn)
 			RCU_INIT_POINTER(*(void __rcu __force **)&cgrp->kn->priv,
 					 NULL);
+
+		cgroup_bpf_put(cgrp);
 	}
 
 	mutex_unlock(&cgroup_mutex);

@@ -5245,6 +5247,9 @@ static struct cgroup *cgroup_create(struct cgroup *parent)
 	if (!cgroup_on_dfl(cgrp))
 		cgrp->subtree_control = cgroup_control(cgrp);
 
+	if (parent)
+		cgroup_bpf_inherit(cgrp, parent);
+
 	cgroup_propagate_control(cgrp);
 
 	/* @cgrp doesn't have dir yet so the following will only create csses */

@@ -6417,6 +6422,19 @@ static __init int cgroup_namespaces_init(void)
 }
 subsys_initcall(cgroup_namespaces_init);
 
+#ifdef CONFIG_CGROUP_BPF
+void cgroup_bpf_update(struct cgroup *cgrp,
+		       struct bpf_prog *prog,
+		       enum bpf_attach_type type)
+{
+	struct cgroup *parent = cgroup_parent(cgrp);
+
+	mutex_lock(&cgroup_mutex);
+	__cgroup_bpf_update(cgrp, parent, prog, type);
+	mutex_unlock(&cgroup_mutex);
+}
+#endif /* CONFIG_CGROUP_BPF */
+
 #ifdef CONFIG_CGROUP_DEBUG
 static struct cgroup_subsys_state *
 debug_css_alloc(struct cgroup_subsys_state *parent_css)

-- 
2.5.5

Extend the bpf(2) syscall by two new commands, BPF_PROG_ATTACH and
BPF_PROG_DETACH which allow attaching and detaching eBPF programs
to a target.

On the API level, the target could be anything that has an fd in
userspace, hence the name of the field in union bpf_attr is called
'target_fd'.

When called with BPF_ATTACH_TYPE_CGROUP_INET_{E,IN}GRESS, the target is
expected to be a valid file descriptor of a cgroup v2 directory which
has the bpf controller enabled. These are the only use-cases
implemented by this patch at this point, but more can be added.

If a program of the given type already exists in the given cgroup,
the program is swapped automically, so userspace does not have to drop
an existing program first before installing a new one, which would
otherwise leave a gap in which no program is attached.

For more information on the propagation logic to subcgroups, please
refer to the bpf cgroup controller implementation.

The API is guarded by CAP_NET_ADMIN.

Signed-off-by: Daniel Mack <daniel@zonque.org>
---
 include/uapi/linux/bpf.h |  8 +++++
 kernel/bpf/syscall.c     | 81 ++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 89 insertions(+)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 55f815e..7cd3616 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h

@@ -73,6 +73,8 @@ enum bpf_cmd {
 	BPF_PROG_LOAD,
 	BPF_OBJ_PIN,
 	BPF_OBJ_GET,
+	BPF_PROG_ATTACH,
+	BPF_PROG_DETACH,
 };
 
 enum bpf_map_type {

@@ -150,6 +152,12 @@ union bpf_attr {
 		__aligned_u64	pathname;
 		__u32		bpf_fd;
 	};
+
+	struct { /* anonymous struct used by BPF_PROG_ATTACH/DETACH commands */
+		__u32		target_fd;	/* container object to attach to */
+		__u32		attach_bpf_fd;	/* eBPF program to attach */
+		__u32		attach_type;
+	};
 } __attribute__((aligned(8)));
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 228f962..1a8592a 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c

@@ -822,6 +822,77 @@ static int bpf_obj_get(const union bpf_attr *attr)
 	return bpf_obj_get_user(u64_to_ptr(attr->pathname));
 }
 
+#ifdef CONFIG_CGROUP_BPF
+
+#define BPF_PROG_ATTACH_LAST_FIELD attach_type
+
+static int bpf_prog_attach(const union bpf_attr *attr)
+{
+	struct bpf_prog *prog;
+	struct cgroup *cgrp;
+
+	if (!capable(CAP_NET_ADMIN))
+		return -EPERM;
+
+	if (CHECK_ATTR(BPF_PROG_ATTACH))
+		return -EINVAL;
+
+	switch (attr->attach_type) {
+	case BPF_CGROUP_INET_INGRESS:
+	case BPF_CGROUP_INET_EGRESS:
+		prog = bpf_prog_get_type(attr->attach_bpf_fd,
+					 BPF_PROG_TYPE_CGROUP_SOCKET);
+		if (IS_ERR(prog))
+			return PTR_ERR(prog);
+
+		cgrp = cgroup_get_from_fd(attr->target_fd);
+		if (IS_ERR(cgrp)) {
+			bpf_prog_put(prog);
+			return PTR_ERR(cgrp);
+		}
+
+		cgroup_bpf_update(cgrp, prog, attr->attach_type);
+		cgroup_put(cgrp);
+		break;
+
+	default:
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+#define BPF_PROG_DETACH_LAST_FIELD attach_type
+
+static int bpf_prog_detach(const union bpf_attr *attr)
+{
+	struct cgroup *cgrp;
+
+	if (!capable(CAP_NET_ADMIN))
+		return -EPERM;
+
+	if (CHECK_ATTR(BPF_PROG_DETACH))
+		return -EINVAL;
+
+	switch (attr->attach_type) {
+	case BPF_CGROUP_INET_INGRESS:
+	case BPF_CGROUP_INET_EGRESS:
+		cgrp = cgroup_get_from_fd(attr->target_fd);
+		if (IS_ERR(cgrp))
+			return PTR_ERR(cgrp);
+
+		cgroup_bpf_update(cgrp, NULL, attr->attach_type);
+		cgroup_put(cgrp);
+		break;
+
+	default:
+		return -EINVAL;
+	}
+
+	return 0;
+}
+#endif /* CONFIG_CGROUP_BPF */
+
 SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, size)
 {
 	union bpf_attr attr = {};

@@ -888,6 +959,16 @@ SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, siz
 	case BPF_OBJ_GET:
 		err = bpf_obj_get(&attr);
 		break;
+
+#ifdef CONFIG_CGROUP_BPF
+	case BPF_PROG_ATTACH:
+		err = bpf_prog_attach(&attr);
+		break;
+	case BPF_PROG_DETACH:
+		err = bpf_prog_detach(&attr);
+		break;
+#endif
+
 	default:
 		err = -EINVAL;
 		break;

-- 
2.5.5

Hi,

On Mon, Sep 12, 2016 at 06:12:09PM +0200, Daniel Mack wrote:

This is v5 of the patch set to allow eBPF programs for network
filtering and accounting to be attached to cgroups, so that they apply
to all sockets of all tasks placed in that cgroup. The logic also
allows to be extendeded for other cgroup based eBPF logic.

1) This infrastructure can only be useful to systemd, or any similar
   orchestration daemon. Look, you can only apply filtering policies
   to processes that are launched by systemd, so this only works
   for server processes. For client processes this infrastructure is
   *racy*, you have to add new processes in runtime to the cgroup,
   thus there will be time some little time where no filtering policy
   will be applied. For quality of service, this may be an acceptable
   race, but this is aiming to deploy a filtering policy.

2) This aproach looks uninfrastructured to me. This provides a hook
   to push a bpf blob at a place in the stack that deploys a filtering
   policy that is not visible to others. We have interfaces that allows
   us to dump the filtering policy that is being applied, report events
   to enable cooperation between several processes with similar
   capabilities and so on.  For the XDP thing, this ability to push
   blobs may be fine as long as it will not interfer with the stack so
   we can provide an alternative to DPDK in Linux. For tracing, that's
   fine too since it is innocuous. And likely for other applications is
   a good fit. But I don't think this is the case.

After chatting with Daniel Borkmann and Alexei off-list, we concluded
that __dev_queue_xmit() is the place where the egress hooks should live
when eBPF programs need access to the L2 bits of the skb.

3) This egress hook is coming very late, the only reason I find to
   place it at __dev_queue_xmit() is that bpf naturally works with
   layer 2 information in place. But this new hook is placed in
   _everyone's output ath_ that only works for the very specific
   usecase I exposed above.

The main concern during the workshop was that a hook only for cgroups
is too specific, but this is actually even more specific than this.

I have nothing against systemd or the needs for more
programmability/flexibility in the stack, but I think this needs to
fulfill some requirements to fit into the infrastructure that we have
in the right way.

Hi,

On 09/13/2016 01:56 PM, Pablo Neira Ayuso wrote:

On Mon, Sep 12, 2016 at 06:12:09PM +0200, Daniel Mack wrote:

quoted

This is v5 of the patch set to allow eBPF programs for network
filtering and accounting to be attached to cgroups, so that they apply
to all sockets of all tasks placed in that cgroup. The logic also
allows to be extendeded for other cgroup based eBPF logic.

1) This infrastructure can only be useful to systemd, or any similar
   orchestration daemon. Look, you can only apply filtering policies
   to processes that are launched by systemd, so this only works
   for server processes.

Sorry, but both statements aren't true. The eBPF policies apply to every
process that is placed in a cgroup, and my example program in 6/6 shows
how that can be done from the command line. Also, systemd is able to
control userspace processes just fine, and it not limited to 'server
processes'.

For client processes this infrastructure is
   *racy*, you have to add new processes in runtime to the cgroup,
   thus there will be time some little time where no filtering policy
   will be applied. For quality of service, this may be an acceptable
   race, but this is aiming to deploy a filtering policy.

That's a limitation that applies to many more control mechanisms in the
kernel, and it's something that can easily be solved with fork+exec.

2) This aproach looks uninfrastructured to me. This provides a hook
   to push a bpf blob at a place in the stack that deploys a filtering
   policy that is not visible to others.

That's just as transparent as SO_ATTACH_FILTER. What kind of
introspection mechanism do you have in mind?

We have interfaces that allows
   us to dump the filtering policy that is being applied, report events
   to enable cooperation between several processes with similar
   capabilities and so on.

Well, in practice, for netfilter, there can only be one instance in the
system that acts as central authoritative, otherwise you'll end up with
orphaned entries or with situation where some client deletes rules
behind the back of the one that originally installed it. So I really
think there is nothing wrong with demanding a single, privileged
controller to manage things.

quoted

After chatting with Daniel Borkmann and Alexei off-list, we concluded
that __dev_queue_xmit() is the place where the egress hooks should live
when eBPF programs need access to the L2 bits of the skb.

3) This egress hook is coming very late, the only reason I find to
   place it at __dev_queue_xmit() is that bpf naturally works with
   layer 2 information in place. But this new hook is placed in
   _everyone's output ath_ that only works for the very specific
   usecase I exposed above.

It's about filtering outgoing network packets of applications, and
providing them with L2 information for filtering purposes. I don't think
that's a very specific use-case.

When the feature is not used at all, the added costs on the output path
are close to zero, due to the use of static branches. If used somewhere
in the system but not for the packet in flight, costs are slightly
higher but acceptable. In fact, it's not even measurable in my tests
here. How is that different from the netfilter OUTPUT hook, btw?

That said, limiting it to L3 is still an option. It's just that we need
ingress and egress to be in sync, so both would be L3 then. So far, the
possible advantages for future use-cases having access to L2 outweighed
the concerns of putting the hook to dev_queue_xmit(), but I'm open to
discussing that.

The main concern during the workshop was that a hook only for cgroups
is too specific, but this is actually even more specific than this.

This patch set merely implements an infrastructure that can accommodate
many more things as well in the future. We could, in theory, even add
hooks for forwarded packets specifically, or other eBPF programs, not
even for network filtering etc.

I have nothing against systemd or the needs for more
programmability/flexibility in the stack, but I think this needs to
fulfill some requirements to fit into the infrastructure that we have
in the right way.

Well, as I explained already, this patch set results from endless
discussions that went nowhere, about how such a thing can be achieved
with netfilter.


Thanks,
Daniel

 ❦ 12 septembre 2016 18:12 CEST, Daniel Mack [off-list ref] :

* The sample program learned to support both ingress and egress, and
  can now optionally make the eBPF program drop packets by making it
  return 0.

Ability to lock the eBPF program to avoid modification from a later
program or in a subcgroup would be pretty interesting from a security
perspective.
-- 
Use recursive procedures for recursively-defined data structures.
            - The Elements of Programming Style (Kernighan & Plauger)