rds_tcp: close NULL deref window in rds_tcp_set_callbacks

rds_tcp_set_callbacks() links a new rds_tcp_connection onto
rds_tcp_tc_list under rds_tcp_tc_list_lock. It releases the
lock, then assigns tc->t_sock = sock outside the lock.

rds_tcp_tc_info() and rds6_tcp_tc_info() walk rds_tcp_tc_list
under the same lock. Both dereference tc->t_sock->sk without
a NULL check.

A reader can acquire rds_tcp_tc_list_lock between the writer's
spin_unlock and the t_sock store. It then sees a list entry
whose t_sock is NULL. The dereference of tc->t_sock->sk is a
NULL access.

Move tc->t_sock = sock inside rds_tcp_tc_list_lock, before
list_add_tail. A reader holding the lock then observes the
linkage and the t_sock store together.

The restore path is safe. rds_tcp_restore_callbacks() does
list_del_init inside the lock. The matching tc->t_sock = NULL
after unlink is harmless to readers holding the lock.

Fixes: 70041088e3b9 ("RDS: Add TCP transport to RDS")
Suggested-by: Simon Horman <horms@kernel.org>
Signed-off-by: Maoyi Xie <maoyi.xie@ntu.edu.sg>
Reviewed-by: Allison Henderson <achender@kernel.org>
Link: https://patch.msgid.link/20260512142807.1855619-1-maoyi.xie@ntu.edu.sg
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/rds/tcp.c b/net/rds/tcp.c
index 654e23d13e3dfb6d242b3b8741a0b4761308198d..5830b31a1f37b3e380a58eab043ea3162d18fae5 100644 (file)
--- a/net/rds/tcp.c
+++ b/net/rds/tcp.c
@@ -198,8 +198,13 @@ void rds_tcp_set_callbacks(struct socket *sock, struct rds_conn_path *cp)
        rdsdebug("setting sock %p callbacks to tc %p\n", sock, tc);
        write_lock_bh(&sock->sk->sk_callback_lock);
 
-       /* done under the callback_lock to serialize with write_space */
+       /* done under the callback_lock to serialize with write_space.
+        * Set t_sock inside rds_tcp_tc_list_lock so readers walking
+        * rds_tcp_tc_list under the same lock cannot observe an
+        * entry whose t_sock is NULL.
+        */
        spin_lock(&rds_tcp_tc_list_lock);
+       tc->t_sock = sock;
        list_add_tail(&tc->t_list_item, &rds_tcp_tc_list);
 #if IS_ENABLED(CONFIG_IPV6)
        rds6_tcp_tc_count++;
@@ -211,8 +216,6 @@ void rds_tcp_set_callbacks(struct socket *sock, struct rds_conn_path *cp)
        /* accepted sockets need our listen data ready undone */
        if (sock->sk->sk_data_ready == rds_tcp_listen_data_ready)
                sock->sk->sk_data_ready = sock->sk->sk_user_data;
-
-       tc->t_sock = sock;
        if (!tc->t_rtn)
                tc->t_rtn = net_generic(sock_net(sock->sk), rds_tcp_netid);
        tc->t_cpath = cp;