When IPV6_MROUTE_MULTIPLE_TABLES is enabled, multicast routing tables
must be read under RCU or RTNL lock.

In case ip6mr_mfc_seq_start() fails with an error (currently not
possible, as RT6_TABLE_DFLT always exists, ip6mr_get_table() cannot fail
in this case), ip6mr_mfc_seq_stop() would be called and release the RCU
lock.

Fixes: d1db275dd3f6 ("ipv6: ip6mr: support multiple tables")
Signed-off-by: Stefan Wiehler <stefan.wiehler@nokia.com>
---
 net/ipv6/ip6mr.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/net/ipv6/ip6mr.c b/net/ipv6/ip6mr.c
index 9bf42aafc7f0..90d0f09cdd4e 100644
--- a/net/ipv6/ip6mr.c
+++ b/net/ipv6/ip6mr.c
@@ -464,10 +464,12 @@ static const struct seq_operations ip6mr_vif_seq_ops = {
 };
 
 static void *ipmr_mfc_seq_start(struct seq_file *seq, loff_t *pos)
+	__acquires(RCU)
 {
 	struct net *net = seq_file_net(seq);
 	struct mr_table *mrt;
 
+	rcu_read_lock();
 	mrt = ip6mr_get_table(net, RT6_TABLE_DFLT);
 	if (!mrt)
 		return ERR_PTR(-ENOENT);
@@ -475,6 +477,12 @@ static void *ipmr_mfc_seq_start(struct seq_file *seq, loff_t *pos)
 	return mr_mfc_seq_start(seq, pos, mrt, &mfc_unres_lock);
 }
 
+static void ipmr_mfc_seq_stop(struct seq_file *seq, void *v)
+	__releases(RCU)
+{
+	rcu_read_unlock();
+}
+
 static int ipmr_mfc_seq_show(struct seq_file *seq, void *v)
 {
 	int n;
@@ -520,7 +528,7 @@ static int ipmr_mfc_seq_show(struct seq_file *seq, void *v)
 static const struct seq_operations ipmr_mfc_seq_ops = {
 	.start = ipmr_mfc_seq_start,
 	.next  = mr_mfc_seq_next,
-	.stop  = mr_mfc_seq_stop,
+	.stop  = ipmr_mfc_seq_stop,
 	.show  = ipmr_mfc_seq_show,
 };
 #endif
-- 
2.42.0