linux-kernel - [PATCH 3.16 147/366] l2tp: hold reference on tunnels printed in l2tp/tunnels debugfs file

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Message-ID: <lsq.1539530741.816498408@decadent.org.uk>
Date:   Sun, 14 Oct 2018 16:25:41 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Guillaume Nault" <g.nault@...halink.fr>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 3.16 147/366] l2tp: hold reference on tunnels printed in
 l2tp/tunnels debugfs file

3.16.60-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Guillaume Nault <g.nault@...halink.fr>

commit f726214d9b23e5fce8c11937577a289a3202498f upstream.

Use l2tp_tunnel_get_nth() instead of l2tp_tunnel_find_nth(), to be safe
against concurrent tunnel deletion.

Use the same mechanism as in l2tp_ppp.c for dropping the reference
taken by l2tp_tunnel_get_nth(). That is, drop the reference just
before looking up the next tunnel. In case of error, drop the last
accessed tunnel in l2tp_dfs_seq_stop().

That was the last use of l2tp_tunnel_find_nth().

Fixes: 0ad6614048cf ("l2tp: Add debugfs files for dumping l2tp debug info")
Signed-off-by: Guillaume Nault <g.nault@...halink.fr>
Signed-off-by: David S. Miller <davem@...emloft.net>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 net/l2tp/l2tp_core.c    | 20 --------------------
 net/l2tp/l2tp_core.h    |  1 -
 net/l2tp/l2tp_debugfs.c | 15 +++++++++++++--
 3 files changed, 13 insertions(+), 23 deletions(-)

--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -415,26 +415,6 @@ err_tlock:
 }
 EXPORT_SYMBOL_GPL(l2tp_session_register);
 
-struct l2tp_tunnel *l2tp_tunnel_find_nth(struct net *net, int nth)
-{
-	struct l2tp_net *pn = l2tp_pernet(net);
-	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) {
-			rcu_read_unlock_bh();
-			return tunnel;
-		}
-	}
-
-	rcu_read_unlock_bh();
-
-	return NULL;
-}
-EXPORT_SYMBOL_GPL(l2tp_tunnel_find_nth);
-
 /*****************************************************************************
  * Receive data handling
  *****************************************************************************/
--- a/net/l2tp/l2tp_core.h
+++ b/net/l2tp/l2tp_core.h
@@ -242,7 +242,6 @@ struct l2tp_session *l2tp_session_get_nt
 struct l2tp_session *l2tp_session_get_by_ifname(const struct net *net,
 						const char *ifname,
 						bool do_ref);
-struct l2tp_tunnel *l2tp_tunnel_find_nth(struct net *net, int nth);
 
 int l2tp_tunnel_create(struct net *net, int fd, int version, u32 tunnel_id,
 		       u32 peer_tunnel_id, struct l2tp_tunnel_cfg *cfg,
--- a/net/l2tp/l2tp_debugfs.c
+++ b/net/l2tp/l2tp_debugfs.c
@@ -47,7 +47,11 @@ struct l2tp_dfs_seq_data {
 
 static void l2tp_dfs_next_tunnel(struct l2tp_dfs_seq_data *pd)
 {
-	pd->tunnel = l2tp_tunnel_find_nth(pd->net, pd->tunnel_idx);
+	/* Drop reference taken during previous invocation */
+	if (pd->tunnel)
+		l2tp_tunnel_dec_refcount(pd->tunnel);
+
+	pd->tunnel = l2tp_tunnel_get_nth(pd->net, pd->tunnel_idx);
 	pd->tunnel_idx++;
 }
 
@@ -96,7 +100,14 @@ static void *l2tp_dfs_seq_next(struct se
 
 static void l2tp_dfs_seq_stop(struct seq_file *p, void *v)
 {
-	/* nothing to do */
+	struct l2tp_dfs_seq_data *pd = v;
+
+	if (!pd || pd == SEQ_START_TOKEN)
+		return;
+
+	/* Drop reference taken by last invocation of l2tp_dfs_next_tunnel() */
+	if (pd->tunnel)
+		l2tp_tunnel_dec_refcount(pd->tunnel);
 }
 
 static void l2tp_dfs_seq_tunnel_show(struct seq_file *m, void *v)