Re: [syzbot] [net?] [bpf?] possible deadlock in sock_hash_delete_elem (2)

From: Tetsuo Handa
Date: Sun May 12 2024 - 02:30:09 EST


#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

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)