Subject: [PATCH bpf 1/4] bpf: remove __rcu annotations from bpf_prog_array

From: Stanislav Fomichev <[email-masked]>
Date: Wed, 8 May 2019 10:18:42 -0700

Drop __rcu annotations and rcu read sections. That's not needed since
all existing callers call those helpers from the rcu update side
and under a mutex. This guarantees that use-after-free could not
happen. In the next patches I'll fix the callers with missing
rcu_dereference_protected to make sparse/lockdep happy.

Signed-off-by: Stanislav Fomichev <[email-masked]>
---
 include/linux/bpf.h | 12 ++++++------
 kernel/bpf/core.c   | 31 ++++++++++++-------------------
 2 files changed, 18 insertions(+), 25 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 944ccc310201..b90d2859bc60 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -476,17 +476,17 @@ struct bpf_prog_array {
 };
 
 struct bpf_prog_array *bpf_prog_array_alloc(u32 prog_cnt, gfp_t flags);
-void bpf_prog_array_free(struct bpf_prog_array __rcu *progs);
-int bpf_prog_array_length(struct bpf_prog_array __rcu *progs);
-int bpf_prog_array_copy_to_user(struct bpf_prog_array __rcu *progs,
+void bpf_prog_array_free(struct bpf_prog_array *progs);
+int bpf_prog_array_length(struct bpf_prog_array *progs);
+int bpf_prog_array_copy_to_user(struct bpf_prog_array *progs,
 				__u32 __user *prog_ids, u32 cnt);
 
-void bpf_prog_array_delete_safe(struct bpf_prog_array __rcu *progs,
+void bpf_prog_array_delete_safe(struct bpf_prog_array *progs,
 				struct bpf_prog *old_prog);
-int bpf_prog_array_copy_info(struct bpf_prog_array __rcu *array,
+int bpf_prog_array_copy_info(struct bpf_prog_array *array,
 			     u32 *prog_ids, u32 request_cnt,
 			     u32 *prog_cnt);
-int bpf_prog_array_copy(struct bpf_prog_array __rcu *old_array,
+int bpf_prog_array_copy(struct bpf_prog_array *old_array,
 			struct bpf_prog *exclude_prog,
 			struct bpf_prog *include_prog,
 			struct bpf_prog_array **new_array);
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index ff09d32a8a1b..da03fbc811fd 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -1794,38 +1794,33 @@ struct bpf_prog_array *bpf_prog_array_alloc(u32 prog_cnt, gfp_t flags)
 	return &empty_prog_array.hdr;
 }
 
-void bpf_prog_array_free(struct bpf_prog_array __rcu *progs)
+void bpf_prog_array_free(struct bpf_prog_array *progs)
 {
-	if (!progs ||
-	    progs == (struct bpf_prog_array __rcu *)&empty_prog_array.hdr)
+	if (!progs || progs == &empty_prog_array.hdr)
 		return;
 	kfree_rcu(progs, rcu);
 }
 
-int bpf_prog_array_length(struct bpf_prog_array __rcu *array)
+int bpf_prog_array_length(struct bpf_prog_array *array)
 {
 	struct bpf_prog_array_item *item;
 	u32 cnt = 0;
 
-	rcu_read_lock();
-	item = rcu_dereference(array)->items;
-	for (; item->prog; item++)
+	for (item = array->items; item->prog; item++)
 		if (item->prog != &dummy_bpf_prog.prog)
 			cnt++;
-	rcu_read_unlock();
 	return cnt;
 }

-static bool bpf_prog_array_copy_core(struct bpf_prog_array __rcu *array,
+static bool bpf_prog_array_copy_core(struct bpf_prog_array *array,
 				     u32 *prog_ids,
 				     u32 request_cnt)
 {
 	struct bpf_prog_array_item *item;
 	int i = 0;
 
-	item = rcu_dereference_check(array, 1)->items;
-	for (; item->prog; item++) {
+	for (item = array->items; item->prog; item++) {
 		if (item->prog == &dummy_bpf_prog.prog)
 			continue;
 		prog_ids[i] = item->prog->aux->id;
@@ -1838,7 +1833,7 @@ static bool bpf_prog_array_copy_core(struct bpf_prog_array __rcu *array,
 	return !!(item->prog);
 }
 
-int bpf_prog_array_copy_to_user(struct bpf_prog_array __rcu *array,
+int bpf_prog_array_copy_to_user(struct bpf_prog_array *array,
 				__u32 __user *prog_ids, u32 cnt)
 {
 	unsigned long err = 0;
@@ -1858,9 +1853,7 @@ int bpf_prog_array_copy_to_user(struct bpf_prog_array __rcu *array,
 	ids = kcalloc(cnt, sizeof(u32), GFP_USER | __GFP_NOWARN);
 	if (!ids)
 		return -ENOMEM;
-	rcu_read_lock();
 	nospc = bpf_prog_array_copy_core(array, ids, cnt);
-	rcu_read_unlock();
 	err = copy_to_user(prog_ids, ids, cnt * sizeof(u32));
 	kfree(ids);
 	if (err)
@@ -1870,19 +1863,19 @@ int bpf_prog_array_copy_to_user(struct bpf_prog_array __rcu *array,
 	return 0;
 }
 
-void bpf_prog_array_delete_safe(struct bpf_prog_array __rcu *array,
+void bpf_prog_array_delete_safe(struct bpf_prog_array *array,
 				struct bpf_prog *old_prog)
 {
-	struct bpf_prog_array_item *item = array->items;
+	struct bpf_prog_array_item *item;
 
-	for (; item->prog; item++)
+	for (item = array->items; item->prog; item++)
 		if (item->prog == old_prog) {
 			WRITE_ONCE(item->prog, &dummy_bpf_prog.prog);
 			break;
 		}
 }
 
-int bpf_prog_array_copy(struct bpf_prog_array __rcu *old_array,
+int bpf_prog_array_copy(struct bpf_prog_array *old_array,
 			struct bpf_prog *exclude_prog,
 			struct bpf_prog *include_prog,
 			struct bpf_prog_array **new_array)
@@ -1946,7 +1939,7 @@ int bpf_prog_array_copy(struct bpf_prog_array __rcu *old_array,
 	return 0;
 }
 
-int bpf_prog_array_copy_info(struct bpf_prog_array __rcu *array,
+int bpf_prog_array_copy_info(struct bpf_prog_array *array,
 			     u32 *prog_ids, u32 request_cnt,
 			     u32 *prog_cnt)
 {
-- 
2.21.0.1020.gf2820cf01a-goog