From c4d48a58f32c5972174a1d01c33b296fe378cce0 Mon Sep 17 00:00:00 2001 From: Cong Wang Date: Fri, 13 Jan 2023 19:01:36 -0800 Subject: [PATCH 1/2] l2tp: convert l2tp_tunnel_list to idr l2tp uses l2tp_tunnel_list to track all registered tunnels and to allocate tunnel ID's. IDR can do the same job. More importantly, with IDR we can hold the ID before a successful registration so that we don't need to worry about late error handling, it is not easy to rollback socket changes. This is a preparation for the following fix. Cc: Tetsuo Handa Cc: Guillaume Nault Cc: Jakub Sitnicki Cc: Eric Dumazet Cc: Tom Parkin Signed-off-by: Cong Wang Reviewed-by: Guillaume Nault Signed-off-by: David S. Miller --- net/l2tp/l2tp_core.c | 85 ++++++++++++++++++++++---------------------- 1 file changed, 42 insertions(+), 43 deletions(-) diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c index 9a1415fe3fa78..e9c0ce0b7972d 100644 --- a/net/l2tp/l2tp_core.c +++ b/net/l2tp/l2tp_core.c @@ -104,9 +104,9 @@ static struct workqueue_struct *l2tp_wq; /* per-net private data for this module */ static unsigned int l2tp_net_id; struct l2tp_net { - struct list_head l2tp_tunnel_list; - /* Lock for write access to l2tp_tunnel_list */ - spinlock_t l2tp_tunnel_list_lock; + /* Lock for write access to l2tp_tunnel_idr */ + spinlock_t l2tp_tunnel_idr_lock; + struct idr l2tp_tunnel_idr; struct hlist_head l2tp_session_hlist[L2TP_HASH_SIZE_2]; /* Lock for write access to l2tp_session_hlist */ spinlock_t l2tp_session_hlist_lock; @@ -208,13 +208,10 @@ struct l2tp_tunnel *l2tp_tunnel_get(const struct net *net, u32 tunnel_id) struct l2tp_tunnel *tunnel; rcu_read_lock_bh(); - list_for_each_entry_rcu(tunnel, &pn->l2tp_tunnel_list, list) { - if (tunnel->tunnel_id == tunnel_id && - refcount_inc_not_zero(&tunnel->ref_count)) { - rcu_read_unlock_bh(); - - return tunnel; - } + tunnel = idr_find(&pn->l2tp_tunnel_idr, tunnel_id); + if (tunnel && refcount_inc_not_zero(&tunnel->ref_count)) { + rcu_read_unlock_bh(); + return tunnel; } rcu_read_unlock_bh(); @@ -224,13 +221,14 @@ EXPORT_SYMBOL_GPL(l2tp_tunnel_get); struct l2tp_tunnel *l2tp_tunnel_get_nth(const struct net *net, int nth) { - const struct l2tp_net *pn = l2tp_pernet(net); + struct l2tp_net *pn = l2tp_pernet(net); + unsigned long tunnel_id, tmp; struct l2tp_tunnel *tunnel; int count = 0; rcu_read_lock_bh(); - list_for_each_entry_rcu(tunnel, &pn->l2tp_tunnel_list, list) { - if (++count > nth && + idr_for_each_entry_ul(&pn->l2tp_tunnel_idr, tunnel, tmp, tunnel_id) { + if (tunnel && ++count > nth && refcount_inc_not_zero(&tunnel->ref_count)) { rcu_read_unlock_bh(); return tunnel; @@ -1227,6 +1225,15 @@ static void l2tp_udp_encap_destroy(struct sock *sk) l2tp_tunnel_delete(tunnel); } +static void l2tp_tunnel_remove(struct net *net, struct l2tp_tunnel *tunnel) +{ + struct l2tp_net *pn = l2tp_pernet(net); + + spin_lock_bh(&pn->l2tp_tunnel_idr_lock); + idr_remove(&pn->l2tp_tunnel_idr, tunnel->tunnel_id); + spin_unlock_bh(&pn->l2tp_tunnel_idr_lock); +} + /* Workqueue tunnel deletion function */ static void l2tp_tunnel_del_work(struct work_struct *work) { @@ -1234,7 +1241,6 @@ static void l2tp_tunnel_del_work(struct work_struct *work) del_work); struct sock *sk = tunnel->sock; struct socket *sock = sk->sk_socket; - struct l2tp_net *pn; l2tp_tunnel_closeall(tunnel); @@ -1248,12 +1254,7 @@ static void l2tp_tunnel_del_work(struct work_struct *work) } } - /* Remove the tunnel struct from the tunnel list */ - pn = l2tp_pernet(tunnel->l2tp_net); - spin_lock_bh(&pn->l2tp_tunnel_list_lock); - list_del_rcu(&tunnel->list); - spin_unlock_bh(&pn->l2tp_tunnel_list_lock); - + l2tp_tunnel_remove(tunnel->l2tp_net, tunnel); /* drop initial ref */ l2tp_tunnel_dec_refcount(tunnel); @@ -1455,12 +1456,19 @@ static int l2tp_validate_socket(const struct sock *sk, const struct net *net, int l2tp_tunnel_register(struct l2tp_tunnel *tunnel, struct net *net, struct l2tp_tunnel_cfg *cfg) { - struct l2tp_tunnel *tunnel_walk; - struct l2tp_net *pn; + struct l2tp_net *pn = l2tp_pernet(net); + u32 tunnel_id = tunnel->tunnel_id; struct socket *sock; struct sock *sk; int ret; + spin_lock_bh(&pn->l2tp_tunnel_idr_lock); + ret = idr_alloc_u32(&pn->l2tp_tunnel_idr, NULL, &tunnel_id, tunnel_id, + GFP_ATOMIC); + spin_unlock_bh(&pn->l2tp_tunnel_idr_lock); + if (ret) + return ret == -ENOSPC ? -EEXIST : ret; + if (tunnel->fd < 0) { ret = l2tp_tunnel_sock_create(net, tunnel->tunnel_id, tunnel->peer_tunnel_id, cfg, @@ -1481,23 +1489,13 @@ int l2tp_tunnel_register(struct l2tp_tunnel *tunnel, struct net *net, rcu_assign_sk_user_data(sk, tunnel); write_unlock_bh(&sk->sk_callback_lock); - tunnel->l2tp_net = net; - pn = l2tp_pernet(net); - sock_hold(sk); tunnel->sock = sk; + tunnel->l2tp_net = net; - spin_lock_bh(&pn->l2tp_tunnel_list_lock); - list_for_each_entry(tunnel_walk, &pn->l2tp_tunnel_list, list) { - if (tunnel_walk->tunnel_id == tunnel->tunnel_id) { - spin_unlock_bh(&pn->l2tp_tunnel_list_lock); - sock_put(sk); - ret = -EEXIST; - goto err_sock; - } - } - list_add_rcu(&tunnel->list, &pn->l2tp_tunnel_list); - spin_unlock_bh(&pn->l2tp_tunnel_list_lock); + spin_lock_bh(&pn->l2tp_tunnel_idr_lock); + idr_replace(&pn->l2tp_tunnel_idr, tunnel, tunnel->tunnel_id); + spin_unlock_bh(&pn->l2tp_tunnel_idr_lock); if (tunnel->encap == L2TP_ENCAPTYPE_UDP) { struct udp_tunnel_sock_cfg udp_cfg = { @@ -1523,9 +1521,6 @@ int l2tp_tunnel_register(struct l2tp_tunnel *tunnel, struct net *net, return 0; -err_sock: - write_lock_bh(&sk->sk_callback_lock); - rcu_assign_sk_user_data(sk, NULL); err_inval_sock: write_unlock_bh(&sk->sk_callback_lock); @@ -1534,6 +1529,7 @@ int l2tp_tunnel_register(struct l2tp_tunnel *tunnel, struct net *net, else sockfd_put(sock); err: + l2tp_tunnel_remove(net, tunnel); return ret; } EXPORT_SYMBOL_GPL(l2tp_tunnel_register); @@ -1647,8 +1643,8 @@ static __net_init int l2tp_init_net(struct net *net) struct l2tp_net *pn = net_generic(net, l2tp_net_id); int hash; - INIT_LIST_HEAD(&pn->l2tp_tunnel_list); - spin_lock_init(&pn->l2tp_tunnel_list_lock); + idr_init(&pn->l2tp_tunnel_idr); + spin_lock_init(&pn->l2tp_tunnel_idr_lock); for (hash = 0; hash < L2TP_HASH_SIZE_2; hash++) INIT_HLIST_HEAD(&pn->l2tp_session_hlist[hash]); @@ -1662,11 +1658,13 @@ static __net_exit void l2tp_exit_net(struct net *net) { struct l2tp_net *pn = l2tp_pernet(net); struct l2tp_tunnel *tunnel = NULL; + unsigned long tunnel_id, tmp; int hash; rcu_read_lock_bh(); - list_for_each_entry_rcu(tunnel, &pn->l2tp_tunnel_list, list) { - l2tp_tunnel_delete(tunnel); + idr_for_each_entry_ul(&pn->l2tp_tunnel_idr, tunnel, tmp, tunnel_id) { + if (tunnel) + l2tp_tunnel_delete(tunnel); } rcu_read_unlock_bh(); @@ -1676,6 +1674,7 @@ static __net_exit void l2tp_exit_net(struct net *net) for (hash = 0; hash < L2TP_HASH_SIZE_2; hash++) WARN_ON_ONCE(!hlist_empty(&pn->l2tp_session_hlist[hash])); + idr_destroy(&pn->l2tp_tunnel_idr); } static struct pernet_operations l2tp_net_ops = { From 0b2c59720e65885a394a017d0cf9cab118914682 Mon Sep 17 00:00:00 2001 From: Cong Wang Date: Fri, 13 Jan 2023 19:01:37 -0800 Subject: [PATCH 2/2] l2tp: close all race conditions in l2tp_tunnel_register() The code in l2tp_tunnel_register() is racy in several ways: 1. It modifies the tunnel socket _after_ publishing it. 2. It calls setup_udp_tunnel_sock() on an existing socket without locking. 3. It changes sock lock class on fly, which triggers many syzbot reports. This patch amends all of them by moving socket initialization code before publishing and under sock lock. As suggested by Jakub, the l2tp lockdep class is not necessary as we can just switch to bh_lock_sock_nested(). Fixes: 37159ef2c1ae ("l2tp: fix a lockdep splat") Fixes: 6b9f34239b00 ("l2tp: fix races in tunnel creation") Reported-by: syzbot+52866e24647f9a23403f@syzkaller.appspotmail.com Reported-by: syzbot+94cc2a66fc228b23f360@syzkaller.appspotmail.com Reported-by: Tetsuo Handa Cc: Guillaume Nault Cc: Jakub Sitnicki Cc: Eric Dumazet Cc: Tom Parkin Signed-off-by: Cong Wang Reviewed-by: Guillaume Nault Signed-off-by: David S. Miller --- net/l2tp/l2tp_core.c | 28 ++++++++++++++-------------- 1 file changed, 14 insertions(+), 14 deletions(-) diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c index e9c0ce0b7972d..b6554e32bb12a 100644 --- a/net/l2tp/l2tp_core.c +++ b/net/l2tp/l2tp_core.c @@ -1041,7 +1041,7 @@ static int l2tp_xmit_core(struct l2tp_session *session, struct sk_buff *skb, uns IPCB(skb)->flags &= ~(IPSKB_XFRM_TUNNEL_SIZE | IPSKB_XFRM_TRANSFORMED | IPSKB_REROUTED); nf_reset_ct(skb); - bh_lock_sock(sk); + bh_lock_sock_nested(sk); if (sock_owned_by_user(sk)) { kfree_skb(skb); ret = NET_XMIT_DROP; @@ -1385,8 +1385,6 @@ static int l2tp_tunnel_sock_create(struct net *net, return err; } -static struct lock_class_key l2tp_socket_class; - int l2tp_tunnel_create(int fd, int version, u32 tunnel_id, u32 peer_tunnel_id, struct l2tp_tunnel_cfg *cfg, struct l2tp_tunnel **tunnelp) { @@ -1482,21 +1480,16 @@ int l2tp_tunnel_register(struct l2tp_tunnel *tunnel, struct net *net, } sk = sock->sk; + lock_sock(sk); write_lock_bh(&sk->sk_callback_lock); ret = l2tp_validate_socket(sk, net, tunnel->encap); - if (ret < 0) + if (ret < 0) { + release_sock(sk); goto err_inval_sock; + } rcu_assign_sk_user_data(sk, tunnel); write_unlock_bh(&sk->sk_callback_lock); - sock_hold(sk); - tunnel->sock = sk; - tunnel->l2tp_net = net; - - spin_lock_bh(&pn->l2tp_tunnel_idr_lock); - idr_replace(&pn->l2tp_tunnel_idr, tunnel, tunnel->tunnel_id); - spin_unlock_bh(&pn->l2tp_tunnel_idr_lock); - if (tunnel->encap == L2TP_ENCAPTYPE_UDP) { struct udp_tunnel_sock_cfg udp_cfg = { .sk_user_data = tunnel, @@ -1510,9 +1503,16 @@ int l2tp_tunnel_register(struct l2tp_tunnel *tunnel, struct net *net, tunnel->old_sk_destruct = sk->sk_destruct; sk->sk_destruct = &l2tp_tunnel_destruct; - lockdep_set_class_and_name(&sk->sk_lock.slock, &l2tp_socket_class, - "l2tp_sock"); sk->sk_allocation = GFP_ATOMIC; + release_sock(sk); + + sock_hold(sk); + tunnel->sock = sk; + tunnel->l2tp_net = net; + + spin_lock_bh(&pn->l2tp_tunnel_idr_lock); + idr_replace(&pn->l2tp_tunnel_idr, tunnel, tunnel->tunnel_id); + spin_unlock_bh(&pn->l2tp_tunnel_idr_lock); trace_register_tunnel(tunnel);