[PATCH bpf-next v11 08/13] bpf: hold module for bpf_struct_ops_map.

[thinker.li@gmail.com]

From: Kui-Feng Lee <thinker.li@gmail.com>

To ensure that a module remains accessible whenever a struct_ops object of
a struct_ops type provided by the module is still in use.

Signed-off-by: Kui-Feng Lee <thinker.li@gmail.com>
---
 include/linux/bpf.h          |  1 +
 include/linux/bpf_verifier.h |  1 +
 kernel/bpf/bpf_struct_ops.c  | 40 ++++++++++++++++++++++++++++++++++++
 kernel/bpf/verifier.c        | 10 +++++++++
 4 files changed, 52 insertions(+)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index f0ed874d5ac3..c287f42b2e48 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1626,6 +1626,7 @@ struct bpf_struct_ops {
 	void (*unreg)(void *kdata);
 	int (*update)(void *kdata, void *old_kdata);
 	int (*validate)(void *kdata);
+	struct module *owner;
 	const char *name;
 	struct btf_func_model func_models[BPF_STRUCT_OPS_MAX_NR_MEMBERS];
 };
diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 24213a99cc79..c1461342f19e 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -598,6 +598,7 @@ struct bpf_verifier_env {
 	u32 prev_insn_idx;
 	struct bpf_prog *prog;		/* eBPF program being verified */
 	const struct bpf_verifier_ops *ops;
+	struct module *attach_btf_mod;	/* The owner module of prog->aux->attach_btf */
 	struct bpf_verifier_stack_elem *head; /* stack of verifier states to be processed */
 	int stack_size;			/* number of states to be processed */
 	bool strict_alignment;		/* perform strict pointer alignment checks */
diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
index 2fb1b21f989a..d1af0ebaf02f 100644
--- a/kernel/bpf/bpf_struct_ops.c
+++ b/kernel/bpf/bpf_struct_ops.c
@@ -387,6 +387,7 @@ static long bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key,
 	const struct btf_member *member;
 	const struct btf_type *t = st_ops_desc->type;
 	struct bpf_tramp_links *tlinks;
+	struct module *mod = NULL;
 	void *udata, *kdata;
 	int prog_fd, err;
 	void *image, *image_end;
@@ -424,6 +425,14 @@ static long bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key,
 		goto unlock;
 	}
 
+	if (st_map->btf != btf_vmlinux) {
+		mod = btf_try_get_module(st_map->btf);
+		if (!mod) {
+			err = -EINVAL;
+			goto unlock;
+		}
+	}
+
 	memcpy(uvalue, value, map->value_size);
 
 	udata = &uvalue->data;
@@ -552,6 +561,10 @@ static long bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key,
 		 * can be seen once BPF_STRUCT_OPS_STATE_INUSE is set.
 		 */
 		smp_store_release(&kvalue->state, BPF_STRUCT_OPS_STATE_INUSE);
+		/* Hold the owner module until the struct_ops is
+		 * unregistered
+		 */
+		mod = NULL;
 		goto unlock;
 	}
 
@@ -568,6 +581,7 @@ static long bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key,
 	memset(uvalue, 0, map->value_size);
 	memset(kvalue, 0, map->value_size);
 unlock:
+	module_put(mod);
 	kfree(tlinks);
 	mutex_unlock(&st_map->lock);
 	return err;
@@ -588,6 +602,7 @@ static long bpf_struct_ops_map_delete_elem(struct bpf_map *map, void *key)
 	switch (prev_state) {
 	case BPF_STRUCT_OPS_STATE_INUSE:
 		st_map->st_ops_desc->st_ops->unreg(&st_map->kvalue.data);
+		module_put(st_map->st_ops_desc->st_ops->owner);
 		bpf_map_put(map);
 		return 0;
 	case BPF_STRUCT_OPS_STATE_TOBEFREE:
@@ -675,6 +690,7 @@ static struct bpf_map *bpf_struct_ops_map_alloc(union bpf_attr *attr)
 	size_t st_map_size;
 	struct bpf_struct_ops_map *st_map;
 	const struct btf_type *t, *vt;
+	struct module *mod = NULL;
 	struct bpf_map *map;
 	struct btf *btf;
 	int ret;
@@ -684,6 +700,14 @@ static struct bpf_map *bpf_struct_ops_map_alloc(union bpf_attr *attr)
 		btf = btf_get_by_fd(attr->value_type_btf_obj_fd);
 		if (IS_ERR(btf))
 			return ERR_PTR(PTR_ERR(btf));
+
+		if (btf != btf_vmlinux) {
+			mod = btf_try_get_module(btf);
+			if (!mod) {
+				ret = -EINVAL;
+				goto errout;
+			}
+		}
 	} else {
 		btf = btf_vmlinux;
 		btf_get(btf);
@@ -746,6 +770,8 @@ static struct bpf_map *bpf_struct_ops_map_alloc(union bpf_attr *attr)
 	set_vm_flush_reset_perms(st_map->image);
 	bpf_map_init_from_attr(map, attr);
 
+	module_put(mod);
+
 	return map;
 
 errout_free:
@@ -753,6 +779,7 @@ static struct bpf_map *bpf_struct_ops_map_alloc(union bpf_attr *attr)
 	btf = NULL;		/* has been released */
 errout:
 	btf_put(btf);
+	module_put(mod);
 
 	return ERR_PTR(ret);
 }
@@ -836,6 +863,7 @@ static void bpf_struct_ops_map_link_dealloc(struct bpf_link *link)
 		 * bpf_struct_ops_link_create() fails to register.
 		 */
 		st_map->st_ops_desc->st_ops->unreg(&st_map->kvalue.data);
+		module_put(st_map->st_ops_desc->st_ops->owner);
 		bpf_map_put(&st_map->map);
 	}
 	kfree(st_link);
@@ -882,6 +910,10 @@ static int bpf_struct_ops_map_link_update(struct bpf_link *link, struct bpf_map
 	if (!bpf_struct_ops_valid_to_reg(new_map))
 		return -EINVAL;
 
+	/* The old map is holding the refcount for the owner module.  The
+	 * ownership of the owner module refcount is going to be
+	 * transferred from the old map to the new map.
+	 */
 	if (!st_map->st_ops_desc->st_ops->update)
 		return -EOPNOTSUPP;
 
@@ -927,6 +959,7 @@ int bpf_struct_ops_link_create(union bpf_attr *attr)
 	struct bpf_link_primer link_primer;
 	struct bpf_struct_ops_map *st_map;
 	struct bpf_map *map;
+	struct btf *btf;
 	int err;
 
 	map = bpf_map_get(attr->link_create.map_fd);
@@ -951,8 +984,15 @@ int bpf_struct_ops_link_create(union bpf_attr *attr)
 	if (err)
 		goto err_out;
 
+	/* Hold the owner module until the struct_ops is unregistered. */
+	btf = st_map->btf;
+	if (btf != btf_vmlinux && !btf_try_get_module(btf)) {
+		err = -EINVAL;
+		goto err_out;
+	}
 	err = st_map->st_ops_desc->st_ops->reg(st_map->kvalue.data);
 	if (err) {
+		module_put(st_map->st_ops_desc->st_ops->owner);
 		bpf_link_cleanup(&link_primer);
 		link = NULL;
 		goto err_out;
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 3f446f76d4bf..20d6d9665983 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -20095,6 +20095,14 @@ static int check_struct_ops_btf_id(struct bpf_verifier_env *env)
 	}
 
 	btf = prog->aux->attach_btf;
+	if (btf != btf_vmlinux) {
+		/* Make sure st_ops is valid through the lifetime of env */
+		env->attach_btf_mod = btf_try_get_module(btf);
+		if (!env->attach_btf_mod) {
+			verbose(env, "owner module of btf is not found\n");
+			return -ENOTSUPP;
+		}
+	}
 
 	btf_id = prog->aux->attach_btf_id;
 	st_ops_desc = bpf_struct_ops_find(btf, btf_id);
@@ -20808,6 +20816,8 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr, __u3
 		env->prog->expected_attach_type = 0;
 
 	*prog = env->prog;
+
+	module_put(env->attach_btf_mod);
 err_unlock:
 	if (!is_priv)
 		mutex_unlock(&bpf_verifier_lock);
-- 
2.34.1