[net,v2,1/2] l2tp: convert l2tp_tunnel_list to idr

Commit Message

Cong Wang Jan. 10, 2023, 9 p.m. UTC

From: Cong Wang <[e-mail]>

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 <[e-mail]>
Cc: Guillaume Nault <[e-mail]>
Cc: Jakub Sitnicki <[e-mail]>
Cc: Eric Dumazet <[e-mail]>
Signed-off-by: Cong Wang <[e-mail]>
---
 net/l2tp/l2tp_core.c | 85 ++++++++++++++++++++++----------------------
 1 file changed, 42 insertions(+), 43 deletions(-)

Comments

Tom Parkin Jan. 11, 2023, 11:29 a.m. UTC | #1

On  Tue, Jan 10, 2023 at 13:00:29 -0800, Cong Wang wrote:
> From: Cong Wang <[e-mail]>
> 
> 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 <[e-mail]>
> Cc: Guillaume Nault <[e-mail]>
> Cc: Jakub Sitnicki <[e-mail]>
> Cc: Eric Dumazet <[e-mail]>
> Signed-off-by: Cong Wang <[e-mail]>
> ---
>  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 9a1415fe3fa7..894bc9ff0e71 100644
> --- a/net/l2tp/l2tp_core.c
> +++ b/net/l2tp/l2tp_core.c
<snip>
> @@ -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;
> +

I believe idr_alloc_u32 will return one of ENOSPC or ENOMEM on
failure, whereas previously this ID check explicitly returned EEXIST
when there was an existing tunnel in the list with the specified ID.

The return code is directly reflected back to userspace in the
pppol2tp case at least (via. the connect handler).

I don't know whether the failure return code could be considered part
of the userspace API or not, but should we be trying to return the
same error code for the "that ID is already in use" case?

Paolo Abeni Jan. 12, 2023, 1:18 p.m. UTC | #2

On Wed, 2023-01-11 at 11:29 +0000, Tom Parkin wrote:
> On  Tue, Jan 10, 2023 at 13:00:29 -0800, Cong Wang wrote:
> > From: Cong Wang <[e-mail]>
> > 
> > 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 <[e-mail]>
> > Cc: Guillaume Nault <[e-mail]>
> > Cc: Jakub Sitnicki <[e-mail]>
> > Cc: Eric Dumazet <[e-mail]>
> > Signed-off-by: Cong Wang <[e-mail]>
> > ---
> >  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 9a1415fe3fa7..894bc9ff0e71 100644
> > --- a/net/l2tp/l2tp_core.c
> > +++ b/net/l2tp/l2tp_core.c
> <snip>
> > @@ -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;
> > +
> 
> I believe idr_alloc_u32 will return one of ENOSPC or ENOMEM on
> failure, whereas previously this ID check explicitly returned EEXIST
> when there was an existing tunnel in the list with the specified ID.
> 
> The return code is directly reflected back to userspace in the
> pppol2tp case at least (via. the connect handler).
> 
> I don't know whether the failure return code could be considered part
> of the userspace API or not, but should we be trying to return the
> same error code for the "that ID is already in use" case?

I agree it would be better to preserve this specific error num. I fear
otherwise the patch could break existing applications (e.g. retrying
with a different id vs giving-up depending on the error number)

Thanks!

Paolo

Patch

diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
index 9a1415fe3fa7..894bc9ff0e71 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;
+
 	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 = {