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

Ben Hutchings
2018-10-14T15:25:41Z

From: Guillaume Nault <g.nault@alphalink.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@alphalink.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.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)