[kernel-hardening] [RFC v4 13/18] bpf/cgroup: Replace struct bpf_prog with struct bpf_object

["Mickaël Salaün" <mic@digikod.net>]

This allows CONFIG_CGROUP_BPF to manage different type of pointers
instead of only eBPF programs. This will be useful for the next commits
to support Landlock with cgroups.

Changes since v3:
* do not use an union of pointers but a struct (suggested by Kees Cook)

Signed-off-by: Mickaël Salaün <mic@digikod.net>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Daniel Mack <daniel@zonque.org>
Cc: David S. Miller <davem@davemloft.net>
Cc: Tejun Heo <tj@kernel.org>
Link: https://lkml.kernel.org/r/CAGXu5j+F80XCPSVL0VxAAoTiYk5D1NKKC3jyAU=Z0Gi7L9S0aw@mail.gmail.com
---
 include/linux/bpf-cgroup.h |  8 ++++++--
 kernel/bpf/cgroup.c        | 35 ++++++++++++++++++-----------------
 2 files changed, 24 insertions(+), 19 deletions(-)

diff --git a/include/linux/bpf-cgroup.h b/include/linux/bpf-cgroup.h
index fc076de74ab9..2f608e5d94e9 100644
--- a/include/linux/bpf-cgroup.h
+++ b/include/linux/bpf-cgroup.h
@@ -14,14 +14,18 @@ struct sk_buff;
 extern struct static_key_false cgroup_bpf_enabled_key;
 #define cgroup_bpf_enabled static_branch_unlikely(&cgroup_bpf_enabled_key)
 
+struct bpf_object {
+	struct bpf_prog *prog;
+};
+
 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];
+	struct bpf_object pinned[MAX_BPF_ATTACH_TYPE];
+	struct bpf_object effective[MAX_BPF_ATTACH_TYPE];
 };
 
 void cgroup_bpf_put(struct cgroup *cgrp);
diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
index a0ab43f264b0..75482cd92d56 100644
--- a/kernel/bpf/cgroup.c
+++ b/kernel/bpf/cgroup.c
@@ -20,18 +20,18 @@ DEFINE_STATIC_KEY_FALSE(cgroup_bpf_enabled_key);
 EXPORT_SYMBOL(cgroup_bpf_enabled_key);
 
 /**
- * cgroup_bpf_put() - put references of all bpf programs
+ * cgroup_bpf_put() - put references of all bpf objects
  * @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];
+	for (type = 0; type < ARRAY_SIZE(cgrp->bpf.pinned); type++) {
+		struct bpf_object pinned = cgrp->bpf.pinned[type];
 
-		if (prog) {
-			bpf_prog_put(prog);
+		if (pinned.prog) {
+			bpf_prog_put(pinned.prog);
 			static_branch_dec(&cgroup_bpf_enabled_key);
 		}
 	}
@@ -47,11 +47,12 @@ 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;
+		struct bpf_prog *prog;
 
-		e = rcu_dereference_protected(parent->bpf.effective[type],
-					      lockdep_is_held(&cgroup_mutex));
-		rcu_assign_pointer(cgrp->bpf.effective[type], e);
+		prog = rcu_dereference_protected(
+				parent->bpf.effective[type].prog,
+				lockdep_is_held(&cgroup_mutex));
+		rcu_assign_pointer(cgrp->bpf.effective[type].prog, prog);
 	}
 }
 
@@ -87,13 +88,13 @@ void __cgroup_bpf_update(struct cgroup *cgrp,
 			 struct bpf_prog *prog,
 			 enum bpf_attach_type type)
 {
-	struct bpf_prog *old_prog, *effective;
+	struct bpf_prog *old_prog = NULL, *effective_prog;
 	struct cgroup_subsys_state *pos;
 
-	old_prog = xchg(cgrp->bpf.prog + type, prog);
+	old_prog = xchg(&cgrp->bpf.pinned[type].prog, prog);
 
-	effective = (!prog && parent) ?
-		rcu_dereference_protected(parent->bpf.effective[type],
+	effective_prog = (!prog && parent) ?
+		rcu_dereference_protected(parent->bpf.effective[type].prog,
 					  lockdep_is_held(&cgroup_mutex)) :
 		prog;
 
@@ -101,11 +102,11 @@ void __cgroup_bpf_update(struct cgroup *cgrp,
 		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)
+		if (desc->bpf.pinned[type].prog && desc != cgrp)
 			pos = css_rightmost_descendant(pos);
 		else
-			rcu_assign_pointer(desc->bpf.effective[type],
-					   effective);
+			rcu_assign_pointer(desc->bpf.effective[type].prog,
+					   effective_prog);
 	}
 
 	if (prog)
@@ -151,7 +152,7 @@ int __cgroup_bpf_run_filter(struct sock *sk,
 
 	rcu_read_lock();
 
-	prog = rcu_dereference(cgrp->bpf.effective[type]);
+	prog = rcu_dereference(cgrp->bpf.effective[type].prog);
 	if (prog) {
 		unsigned int offset = skb->data - skb_network_header(skb);
 
-- 
2.9.3