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Subject[PATCH 3.12 71/86] l2tp: take reference on sessions being dumped
Date
From: Guillaume Nault <g.nault@alphalink.fr>

3.12-stable review patch. If anyone has any objections, please let me know.

===============

[ Upstream commit e08293a4ccbcc993ded0fdc46f1e57926b833d63 ]

Take a reference on the sessions returned by l2tp_session_find_nth()
(and rename it l2tp_session_get_nth() to reflect this change), so that
caller is assured that the session isn't going to disappear while
processing it.

For procfs and debugfs handlers, the session is held in the .start()
callback and dropped in .show(). Given that pppol2tp_seq_session_show()
dereferences the associated PPPoL2TP socket and that
l2tp_dfs_seq_session_show() might call pppol2tp_show(), we also need to
call the session's .ref() callback to prevent the socket from going
away from under us.

Fixes: fd558d186df2 ("l2tp: Split pppol2tp patch into separate l2tp and ppp parts")
Fixes: 0ad6614048cf ("l2tp: Add debugfs files for dumping l2tp debug info")
Fixes: 309795f4bec2 ("l2tp: Add netlink control API for L2TP")
Signed-off-by: Guillaume Nault <g.nault@alphalink.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>
---
net/l2tp/l2tp_core.c | 8 ++++++--
net/l2tp/l2tp_core.h | 3 ++-
net/l2tp/l2tp_debugfs.c | 10 +++++++---
net/l2tp/l2tp_netlink.c | 7 +++++--
net/l2tp/l2tp_ppp.c | 10 +++++++---
5 files changed, 27 insertions(+), 11 deletions(-)

diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
index 6639bc27edb9..d5c09cb249ea 100644
--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -280,7 +280,8 @@ struct l2tp_session *l2tp_session_find(struct net *net, struct l2tp_tunnel *tunn
}
EXPORT_SYMBOL_GPL(l2tp_session_find);

-struct l2tp_session *l2tp_session_find_nth(struct l2tp_tunnel *tunnel, int nth)
+struct l2tp_session *l2tp_session_get_nth(struct l2tp_tunnel *tunnel, int nth,
+ bool do_ref)
{
int hash;
struct l2tp_session *session;
@@ -290,6 +291,9 @@ struct l2tp_session *l2tp_session_find_nth(struct l2tp_tunnel *tunnel, int nth)
for (hash = 0; hash < L2TP_HASH_SIZE; hash++) {
hlist_for_each_entry(session, &tunnel->session_hlist[hash], hlist) {
if (++count > nth) {
+ l2tp_session_inc_refcount(session);
+ if (do_ref && session->ref)
+ session->ref(session);
read_unlock_bh(&tunnel->hlist_lock);
return session;
}
@@ -300,7 +304,7 @@ struct l2tp_session *l2tp_session_find_nth(struct l2tp_tunnel *tunnel, int nth)

return NULL;
}
-EXPORT_SYMBOL_GPL(l2tp_session_find_nth);
+EXPORT_SYMBOL_GPL(l2tp_session_get_nth);

/* Lookup a session by interface name.
* This is very inefficient but is only used by management interfaces.
diff --git a/net/l2tp/l2tp_core.h b/net/l2tp/l2tp_core.h
index f8f1089ee8f2..bf8ad2f233fc 100644
--- a/net/l2tp/l2tp_core.h
+++ b/net/l2tp/l2tp_core.h
@@ -241,7 +241,8 @@ out:
extern struct sock *l2tp_tunnel_sock_lookup(struct l2tp_tunnel *tunnel);
extern void l2tp_tunnel_sock_put(struct sock *sk);
extern struct l2tp_session *l2tp_session_find(struct net *net, struct l2tp_tunnel *tunnel, u32 session_id);
-extern struct l2tp_session *l2tp_session_find_nth(struct l2tp_tunnel *tunnel, int nth);
+extern struct l2tp_session *l2tp_session_get_nth(struct l2tp_tunnel *tunnel, int nth,
+ bool do_ref);
extern struct l2tp_session *l2tp_session_find_by_ifname(struct net *net, char *ifname);
extern struct l2tp_tunnel *l2tp_tunnel_find(struct net *net, u32 tunnel_id);
extern struct l2tp_tunnel *l2tp_tunnel_find_nth(struct net *net, int nth);
diff --git a/net/l2tp/l2tp_debugfs.c b/net/l2tp/l2tp_debugfs.c
index 072d7202e182..c6bd783cfb1b 100644
--- a/net/l2tp/l2tp_debugfs.c
+++ b/net/l2tp/l2tp_debugfs.c
@@ -53,7 +53,7 @@ static void l2tp_dfs_next_tunnel(struct l2tp_dfs_seq_data *pd)

static void l2tp_dfs_next_session(struct l2tp_dfs_seq_data *pd)
{
- pd->session = l2tp_session_find_nth(pd->tunnel, pd->session_idx);
+ pd->session = l2tp_session_get_nth(pd->tunnel, pd->session_idx, true);
pd->session_idx++;

if (pd->session == NULL) {
@@ -237,10 +237,14 @@ static int l2tp_dfs_seq_show(struct seq_file *m, void *v)
}

/* Show the tunnel or session context */
- if (pd->session == NULL)
+ if (!pd->session) {
l2tp_dfs_seq_tunnel_show(m, pd->tunnel);
- else
+ } else {
l2tp_dfs_seq_session_show(m, pd->session);
+ if (pd->session->deref)
+ pd->session->deref(pd->session);
+ l2tp_session_dec_refcount(pd->session);
+ }

out:
return 0;
diff --git a/net/l2tp/l2tp_netlink.c b/net/l2tp/l2tp_netlink.c
index 0825ff26e113..490024eaece8 100644
--- a/net/l2tp/l2tp_netlink.c
+++ b/net/l2tp/l2tp_netlink.c
@@ -719,7 +719,7 @@ static int l2tp_nl_cmd_session_dump(struct sk_buff *skb, struct netlink_callback
goto out;
}

- session = l2tp_session_find_nth(tunnel, si);
+ session = l2tp_session_get_nth(tunnel, si, false);
if (session == NULL) {
ti++;
tunnel = NULL;
@@ -729,8 +729,11 @@ static int l2tp_nl_cmd_session_dump(struct sk_buff *skb, struct netlink_callback

if (l2tp_nl_session_send(skb, NETLINK_CB(cb->skb).portid,
cb->nlh->nlmsg_seq, NLM_F_MULTI,
- session) <= 0)
+ session) <= 0) {
+ l2tp_session_dec_refcount(session);
break;
+ }
+ l2tp_session_dec_refcount(session);

si++;
}
diff --git a/net/l2tp/l2tp_ppp.c b/net/l2tp/l2tp_ppp.c
index c3ae2411650c..c06c7ed47b69 100644
--- a/net/l2tp/l2tp_ppp.c
+++ b/net/l2tp/l2tp_ppp.c
@@ -1576,7 +1576,7 @@ static void pppol2tp_next_tunnel(struct net *net, struct pppol2tp_seq_data *pd)

static void pppol2tp_next_session(struct net *net, struct pppol2tp_seq_data *pd)
{
- pd->session = l2tp_session_find_nth(pd->tunnel, pd->session_idx);
+ pd->session = l2tp_session_get_nth(pd->tunnel, pd->session_idx, true);
pd->session_idx++;

if (pd->session == NULL) {
@@ -1703,10 +1703,14 @@ static int pppol2tp_seq_show(struct seq_file *m, void *v)

/* Show the tunnel or session context.
*/
- if (pd->session == NULL)
+ if (!pd->session) {
pppol2tp_seq_tunnel_show(m, pd->tunnel);
- else
+ } else {
pppol2tp_seq_session_show(m, pd->session);
+ if (pd->session->deref)
+ pd->session->deref(pd->session);
+ l2tp_session_dec_refcount(pd->session);
+ }

out:
return 0;
--
2.12.2
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