If a bpf program is using cgroup local storage, allocate
a bpf_cgroup_storage structure automatically on attaching the program
to a cgroup and save the pointer into the corresponding bpf_prog_list
entry.
Analogically, release the cgroup local storage on detaching
of the bpf program.

Signed-off-by: Roman Gushchin <redacted>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Martin KaFai Lau <redacted>
---
 include/linux/bpf-cgroup.h |  1 +
 kernel/bpf/cgroup.c        | 28 ++++++++++++++++++++++++++--
 2 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/include/linux/bpf-cgroup.h b/include/linux/bpf-cgroup.h
index 1b1b4e94d77d..f37347331fdb 100644
--- a/include/linux/bpf-cgroup.h
+++ b/include/linux/bpf-cgroup.h

@@ -42,6 +42,7 @@ struct bpf_cgroup_storage {
 struct bpf_prog_list {
 	struct list_head node;
 	struct bpf_prog *prog;
+	struct bpf_cgroup_storage *storage;
 };
 
 struct bpf_prog_array;

diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
index badabb0b435c..986ff18ef92e 100644
--- a/kernel/bpf/cgroup.c
+++ b/kernel/bpf/cgroup.c

@@ -34,6 +34,8 @@ void cgroup_bpf_put(struct cgroup *cgrp)
 		list_for_each_entry_safe(pl, tmp, progs, node) {
 			list_del(&pl->node);
 			bpf_prog_put(pl->prog);
+			bpf_cgroup_storage_unlink(pl->storage);
+			bpf_cgroup_storage_free(pl->storage);
 			kfree(pl);
 			static_branch_dec(&cgroup_bpf_enabled_key);
 		}

@@ -188,6 +190,7 @@ int __cgroup_bpf_attach(struct cgroup *cgrp, struct bpf_prog *prog,
 {
 	struct list_head *progs = &cgrp->bpf.progs[type];
 	struct bpf_prog *old_prog = NULL;
+	struct bpf_cgroup_storage *storage, *old_storage = NULL;
 	struct cgroup_subsys_state *css;
 	struct bpf_prog_list *pl;
 	bool pl_was_allocated;

@@ -210,6 +213,10 @@ int __cgroup_bpf_attach(struct cgroup *cgrp, struct bpf_prog *prog,
 	if (prog_list_length(progs) >= BPF_CGROUP_MAX_PROGS)
 		return -E2BIG;
 
+	storage = bpf_cgroup_storage_alloc(prog);
+	if (IS_ERR(storage))
+		return -ENOMEM;
+
 	if (flags & BPF_F_ALLOW_MULTI) {
 		list_for_each_entry(pl, progs, node)
 			if (pl->prog == prog)

@@ -217,24 +224,33 @@ int __cgroup_bpf_attach(struct cgroup *cgrp, struct bpf_prog *prog,
 				return -EINVAL;
 
 		pl = kmalloc(sizeof(*pl), GFP_KERNEL);
-		if (!pl)
+		if (!pl) {
+			bpf_cgroup_storage_free(storage);
 			return -ENOMEM;
+		}

+
 		pl_was_allocated = true;
 		pl->prog = prog;
+		pl->storage = storage;
 		list_add_tail(&pl->node, progs);
 	} else {
 		if (list_empty(progs)) {
 			pl = kmalloc(sizeof(*pl), GFP_KERNEL);
-			if (!pl)
+			if (!pl) {
+				bpf_cgroup_storage_free(storage);
 				return -ENOMEM;
+			}
 			pl_was_allocated = true;
 			list_add_tail(&pl->node, progs);
 		} else {
 			pl = list_first_entry(progs, typeof(*pl), node);
 			old_prog = pl->prog;
+			old_storage = pl->storage;
+			bpf_cgroup_storage_unlink(old_storage);
 			pl_was_allocated = false;
 		}
 		pl->prog = prog;
+		pl->storage = storage;
 	}
 
 	cgrp->bpf.flags[type] = flags;

@@ -257,10 +273,13 @@ int __cgroup_bpf_attach(struct cgroup *cgrp, struct bpf_prog *prog,
 	}
 
 	static_branch_inc(&cgroup_bpf_enabled_key);
+	if (old_storage)
+		bpf_cgroup_storage_free(old_storage);
 	if (old_prog) {
 		bpf_prog_put(old_prog);
 		static_branch_dec(&cgroup_bpf_enabled_key);
 	}
+	bpf_cgroup_storage_link(storage, cgrp, type);
 	return 0;
 
 cleanup:

@@ -276,6 +295,9 @@ int __cgroup_bpf_attach(struct cgroup *cgrp, struct bpf_prog *prog,
 
 	/* and cleanup the prog list */
 	pl->prog = old_prog;
+	bpf_cgroup_storage_free(pl->storage);
+	pl->storage = old_storage;
+	bpf_cgroup_storage_link(old_storage, cgrp, type);
 	if (pl_was_allocated) {
 		list_del(&pl->node);
 		kfree(pl);

@@ -356,6 +378,8 @@ int __cgroup_bpf_detach(struct cgroup *cgrp, struct bpf_prog *prog,
 
 	/* now can actually delete it from this cgroup list */
 	list_del(&pl->node);
+	bpf_cgroup_storage_unlink(pl->storage);
+	bpf_cgroup_storage_free(pl->storage);
 	kfree(pl);
 	if (list_empty(progs))
 		/* last program was detached, reset flags to zero */