On Tue, Apr 8, 2025 at 12:31 AM Jiayuan Chen jiayuan.chen@linux.dev wrote:
There are potential concurrency issues, as shown below. ''' CPU0 CPU1 sk_psock_verdict_data_ready: socket *sock = sk->sk_socket if (!sock) return close(fd): ... ops->release() if (!sock->ops) return sock->ops = NULL rcu_call(sock) free(sock) READ_ONCE(sock->ops) ^ use 'sock' after free '''
RCU is not applicable to Unix sockets read path, because the Unix socket implementation itself assumes it's always in process context and heavily uses mutex_lock, so, we can't call read_skb within rcu lock.
Incrementing the psock reference count would not help either, since sock_map_close() does not wait for data_ready() to complete its execution.
While we don't utilize sk_socket here, implementing read_skb at the sock layer instead of socket layer might be architecturally preferable ? However, deferring this optimization as current fix adequately addresses the immediate issue.
Fixes: c63829182c37 ("af_unix: Implement ->psock_update_sk_prot()") Reported-by: syzbot+dd90a702f518e0eac072@syzkaller.appspotmail.com Closes: https://lore.kernel.org/bpf/6734c033.050a0220.2a2fcc.0015.GAE@google.com/ Signed-off-by: Jiayuan Chen jiayuan.chen@linux.dev
net/core/skmsg.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-)
diff --git a/net/core/skmsg.c b/net/core/skmsg.c index 6101c1bb279a..5e913b62929e 100644 --- a/net/core/skmsg.c +++ b/net/core/skmsg.c @@ -1231,17 +1231,24 @@ static int sk_psock_verdict_recv(struct sock *sk, struct sk_buff *skb)
static void sk_psock_verdict_data_ready(struct sock *sk) {
struct socket *sock = sk->sk_socket;
struct socket *sock; const struct proto_ops *ops; int copied; trace_sk_data_ready(sk);
if (unlikely(!sock))
rcu_read_lock();sock = sk->sk_socket;if (unlikely(!sock)) {rcu_read_unlock(); return;} ops = READ_ONCE(sock->ops);
if (!ops || !ops->read_skb)
if (!ops || !ops->read_skb) {rcu_read_unlock(); return;}rcu_read_unlock();
This makes no sense to me. RCU doesn't work this way.
pw-bot: cr