From 6e77507cc06bb2f9eea08a8e1a5d8d28c0a4ec6c Mon Sep 17 00:00:00 2001 From: Jakub Sitnicki Date: Mon, 14 Nov 2022 20:16:19 +0100 Subject: [PATCH] l2tp: Serialize access to sk_user_data with sk_callback_lock sk->sk_user_data has multiple users, which are not compatible with each other. Writers must synchronize by grabbing the sk->sk_callback_lock. l2tp currently fails to grab the lock when modifying the underlying tunnel socket fields. Fix it by adding appropriate locking. We err on the side of safety and grab the sk_callback_lock also inside the sk_destruct callback overridden by l2tp, even though there should be no refs allowing access to the sock at the time when sk_destruct gets called. v4: - serialize write to sk_user_data in l2tp sk_destruct v3: - switch from sock lock to sk_callback_lock - document write-protection for sk_user_data v2: - update Fixes to point to origin of the bug - use real names in Reported/Tested-by tags Cc: Tom Parkin Fixes: 72ecdb28cfd7 ("[L2TP]: PPP over L2TP driver core") Reported-by: Haowei Yan Signed-off-by: Jakub Sitnicki Signed-off-by: David S. Miller --- include/net/sock.h | 2 +- net/l2tp/l2tp_core.c | 19 +++++++++++++------ 2 files changed, 14 insertions(+), 7 deletions(-) diff --git a/include/net/sock.h b/include/net/sock.h index 5db02546941cf..e0517ecc65315 100644 --- a/include/net/sock.h +++ b/include/net/sock.h @@ -323,7 +323,7 @@ struct sk_filter; * @sk_tskey: counter to disambiguate concurrent tstamp requests * @sk_zckey: counter to order MSG_ZEROCOPY notifications * @sk_socket: Identd and reporting IO signals - * @sk_user_data: RPC layer private data + * @sk_user_data: RPC layer private data. Write-protected by @sk_callback_lock. * @sk_frag: cached page frag * @sk_peek_off: current peek_offset value * @sk_send_head: front of stuff to transmit diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c index 7499c51b18502..754fdda8a5f52 100644 --- a/net/l2tp/l2tp_core.c +++ b/net/l2tp/l2tp_core.c @@ -1150,8 +1150,10 @@ static void l2tp_tunnel_destruct(struct sock *sk) } /* Remove hooks into tunnel socket */ + write_lock_bh(&sk->sk_callback_lock); sk->sk_destruct = tunnel->old_sk_destruct; sk->sk_user_data = NULL; + write_unlock_bh(&sk->sk_callback_lock); /* Call the original destructor */ if (sk->sk_destruct) @@ -1469,16 +1471,18 @@ int l2tp_tunnel_register(struct l2tp_tunnel *tunnel, struct net *net, sock = sockfd_lookup(tunnel->fd, &ret); if (!sock) goto err; - - ret = l2tp_validate_socket(sock->sk, net, tunnel->encap); - if (ret < 0) - goto err_sock; } + sk = sock->sk; + write_lock(&sk->sk_callback_lock); + + ret = l2tp_validate_socket(sk, net, tunnel->encap); + if (ret < 0) + goto err_sock; + tunnel->l2tp_net = net; pn = l2tp_pernet(net); - sk = sock->sk; sock_hold(sk); tunnel->sock = sk; @@ -1504,7 +1508,7 @@ int l2tp_tunnel_register(struct l2tp_tunnel *tunnel, struct net *net, setup_udp_tunnel_sock(net, sock, &udp_cfg); } else { - sk->sk_user_data = tunnel; + rcu_assign_sk_user_data(sk, tunnel); } tunnel->old_sk_destruct = sk->sk_destruct; @@ -1518,6 +1522,7 @@ int l2tp_tunnel_register(struct l2tp_tunnel *tunnel, struct net *net, if (tunnel->fd >= 0) sockfd_put(sock); + write_unlock(&sk->sk_callback_lock); return 0; err_sock: @@ -1525,6 +1530,8 @@ err_sock: sock_release(sock); else sockfd_put(sock); + + write_unlock(&sk->sk_callback_lock); err: return ret; } -- 2.39.5