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Patch "l2tp: take reference on sessions being dumped" has been added to the 4.9-stable tree

PATCH [email protected] 1 participant 1 message Apr 29, 2017

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This is a note to let you know that I've just added the patch titled

l2tp: take reference on sessions being dumped

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
l2tp-take-reference-on-sessions-being-dumped.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

Quoted 1 line

From foo@baz Sat Apr 29 08:22:13 CEST 2017

From: Guillaume Nault <[email protected]>
Date: Mon, 3 Apr 2017 12:03:13 +0200
Subject: l2tp: take reference on sessions being dumped

From: Guillaume Nault <[email protected]>

[ 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 <[email protected]>
Signed-off-by David S. Miller <[email protected]>
Signed-off-by Greg Kroah-Hartman <[email protected]>
---
 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(-)
net/l2tp/l2tp_core.c +6 -2
@@ -278,7 +278,8 @@ struct l2tp_session *l2tp_session_find(s
 }
 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;

@@ -288,6 +289,9 @@ struct l2tp_session *l2tp_session_find_n
 	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;
 			}

@@ -298,7 +302,7 @@ struct l2tp_session *l2tp_session_find_n
 
 	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.
net/l2tp/l2tp_core.h +2 -1
@@ -243,7 +243,8 @@ out:
 struct l2tp_session *l2tp_session_find(struct net *net,
 				       struct l2tp_tunnel *tunnel,
 				       u32 session_id);
-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);
 struct l2tp_session *l2tp_session_find_by_ifname(struct net *net, char *ifname);
 struct l2tp_tunnel *l2tp_tunnel_find(struct net *net, u32 tunnel_id);
 struct l2tp_tunnel *l2tp_tunnel_find_nth(struct net *net, int nth);
net/l2tp/l2tp_debugfs.c +7 -3
@@ -53,7 +53,7 @@ static void l2tp_dfs_next_tunnel(struct
 
 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) {

@@ -238,10 +238,14 @@ static int l2tp_dfs_seq_show(struct seq_
 	}
 
 	/* 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;
net/l2tp/l2tp_netlink.c +5 -2
@@ -844,7 +844,7 @@ static int l2tp_nl_cmd_session_dump(stru
 				goto out;
 		}
 
-		session = l2tp_session_find_nth(tunnel, si);
+		session = l2tp_session_get_nth(tunnel, si, false);
 		if (session == NULL) {
 			ti++;
 			tunnel = NULL;

@@ -854,8 +854,11 @@ static int l2tp_nl_cmd_session_dump(stru
 
 		if (l2tp_nl_session_send(skb, NETLINK_CB(cb->skb).portid,
 					 cb->nlh->nlmsg_seq, NLM_F_MULTI,
-					 session, L2TP_CMD_SESSION_GET) < 0)
+					 session, L2TP_CMD_SESSION_GET) < 0) {
+			l2tp_session_dec_refcount(session);
 			break;
+		}
+		l2tp_session_dec_refcount(session);
 
 		si++;
 	}
net/l2tp/l2tp_ppp.c +7 -3
@@ -1555,7 +1555,7 @@ static void pppol2tp_next_tunnel(struct
 
 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) {

@@ -1682,10 +1682,14 @@ static int pppol2tp_seq_show(struct seq_
 
 	/* 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;

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/l2tp-purge-socket-queues-in-the-.destruct-callback.patch queue-4.9/l2tp-hold-tunnel-socket-when-handling-control-frames-in-l2tp_ip-and-l2tp_ip6.patch queue-4.9/l2tp-take-reference-on-sessions-being-dumped.patch queue-4.9/l2tp-fix-ppp-pseudo-wire-auto-loading.patch