[PATCH] bpf, sockmap: defer sk_psock_free_link() using RCU

[Tetsuo Handa]

If a BPF program is attached to kfree() event, calling kfree()
with psock->link_lock held triggers lockdep warning.

Defer kfree() using RCU so that the attached BPF program runs
without holding psock->link_lock.

Reported-by: syzbot+ec941d6e24f633a59172@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=ec941d6e24f633a59172
Tested-by: syzbot+ec941d6e24f633a59172@xxxxxxxxxxxxxxxxxxxxxxxxx
Reported-by: syzbot+a4ed4041b9bea8177ac3@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=a4ed4041b9bea8177ac3
Tested-by: syzbot+a4ed4041b9bea8177ac3@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
---
 include/linux/skmsg.h | 7 +++++--
 net/core/skmsg.c      | 2 ++
 net/core/sock_map.c   | 2 ++
 3 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/include/linux/skmsg.h b/include/linux/skmsg.h
index a509caf823d6..66590f20b777 100644
--- a/include/linux/skmsg.h
+++ b/include/linux/skmsg.h
@@ -66,7 +66,10 @@ enum sk_psock_state_bits {
 };
 
 struct sk_psock_link {
-	struct list_head		list;
+	union {
+		struct list_head	list;
+		struct rcu_head		rcu;
+	};
 	struct bpf_map			*map;
 	void				*link_raw;
 };
@@ -418,7 +421,7 @@ static inline struct sk_psock_link *sk_psock_init_link(void)
 
 static inline void sk_psock_free_link(struct sk_psock_link *link)
 {
-	kfree(link);
+	kfree_rcu(link, rcu);
 }
 
 struct sk_psock_link *sk_psock_link_pop(struct sk_psock *psock);
diff --git a/net/core/skmsg.c b/net/core/skmsg.c
index fd20aae30be2..9cebfeecd3c9 100644
--- a/net/core/skmsg.c
+++ b/net/core/skmsg.c
@@ -791,10 +791,12 @@ static void sk_psock_link_destroy(struct sk_psock *psock)
 {
 	struct sk_psock_link *link, *tmp;
 
+	rcu_read_lock();
 	list_for_each_entry_safe(link, tmp, &psock->link, list) {
 		list_del(&link->list);
 		sk_psock_free_link(link);
 	}
+	rcu_read_unlock();
 }
 
 void sk_psock_stop(struct sk_psock *psock)
diff --git a/net/core/sock_map.c b/net/core/sock_map.c
index 8598466a3805..8bec4b7a8ec7 100644
--- a/net/core/sock_map.c
+++ b/net/core/sock_map.c
@@ -142,6 +142,7 @@ static void sock_map_del_link(struct sock *sk,
 	bool strp_stop = false, verdict_stop = false;
 	struct sk_psock_link *link, *tmp;
 
+	rcu_read_lock();
 	spin_lock_bh(&psock->link_lock);
 	list_for_each_entry_safe(link, tmp, &psock->link, list) {
 		if (link->link_raw == link_raw) {
@@ -159,6 +160,7 @@ static void sock_map_del_link(struct sock *sk,
 		}
 	}
 	spin_unlock_bh(&psock->link_lock);
+	rcu_read_unlock();
 	if (strp_stop || verdict_stop) {
 		write_lock_bh(&sk->sk_callback_lock);
 		if (strp_stop)
-- 
2.34.1