net/rds: Fix NULL pointer dereference in rds_tcp_accept_one

Save a local pointer to new_sock->sk and hold a reference before
installing callbacks in rds_tcp_accept_one. After
rds_tcp_set_callbacks() or rds_tcp_reset_callbacks(), tc->t_sock is
set to new_sock which may race with the shutdown path.  A concurrent
rds_tcp_conn_path_shutdown() may call sock_release(), which sets
new_sock->sk = NULL and may eventually free sk when the refcount
reaches zero.

Subsequent accesses to new_sock->sk->sk_state would dereference NULL,
causing the crash. The fix saves a local sk pointer before callbacks
are installed so that sk_state can be accessed safely even after
new_sock->sk is nulled, and uses sock_hold()/sock_put() to ensure
sk itself remains valid for the duration.

Fixes: 826c1004d4ae ("net/rds: rds_tcp_conn_path_shutdown must not discard messages")
Reported-by: syzbot+96046021045ffe6d7709@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=96046021045ffe6d7709
Signed-off-by: Allison Henderson <achender@kernel.org>
Link: https://patch.msgid.link/20260216222643.2391390-1-achender@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

diff --git a/net/rds/tcp_listen.c b/net/rds/tcp_listen.c
index 6fb5c92..b4ab68a 100644 (file)
--- a/net/rds/tcp_listen.c
+++ b/net/rds/tcp_listen.c
@@ -177,6 +177,7 @@ int rds_tcp_accept_one(struct rds_tcp_net *rtn)
        struct rds_tcp_connection *rs_tcp = NULL;
        int conn_state;
        struct rds_conn_path *cp;
+       struct sock *sk;
        struct in6_addr *my_addr, *peer_addr;
 #if !IS_ENABLED(CONFIG_IPV6)
        struct in6_addr saddr, daddr;
@@ -298,6 +299,17 @@ int rds_tcp_accept_one(struct rds_tcp_net *rtn)
                rds_conn_path_drop(cp, 0);
                goto rst_nsk;
        }
+       /* Save a local pointer to sk and hold a reference before setting
+        * callbacks. Once callbacks are set, a concurrent
+        * rds_tcp_conn_path_shutdown() may call sock_release(), which
+        * sets new_sock->sk to NULL and drops a reference on sk.
+        * The local pointer lets us safely access sk_state below even
+        * if new_sock->sk has been nulled, and sock_hold() keeps sk
+        * itself valid until we are done.
+        */
+       sk = new_sock->sk;
+       sock_hold(sk);
+
        if (rs_tcp->t_sock) {
                /* Duelling SYN has been handled in rds_tcp_accept_one() */
                rds_tcp_reset_callbacks(new_sock, cp);
@@ -316,13 +328,15 @@ int rds_tcp_accept_one(struct rds_tcp_net *rtn)
         * knowing that "rds_tcp_conn_path_shutdown" will
         * dequeue pending messages.
         */
-       if (new_sock->sk->sk_state == TCP_CLOSE_WAIT ||
-           new_sock->sk->sk_state == TCP_LAST_ACK ||
-           new_sock->sk->sk_state == TCP_CLOSE)
+       if (READ_ONCE(sk->sk_state) == TCP_CLOSE_WAIT ||
+           READ_ONCE(sk->sk_state) == TCP_LAST_ACK ||
+           READ_ONCE(sk->sk_state) == TCP_CLOSE)
                rds_conn_path_drop(cp, 0);
        else
                queue_delayed_work(cp->cp_wq, &cp->cp_recv_w, 0);
 
+       sock_put(sk);
+
        new_sock = NULL;
        ret = 0;
        if (conn->c_npaths == 0)