net: avoid reference counter overflows on fib_rules in multicast forwarding

Bob Falken reported that after 4G packets, multicast forwarding stopped
working. This was because of a rule reference counter overflow which
freed the rule as soon as the overflow happend.

This patch solves this by adding the FIB_LOOKUP_NOREF flag to
fib_rules_lookup calls. This is safe even from non-rcu locked sections
as in this case the flag only implies not taking a reference to the rule,
which we don't need at all.

Rules only hold references to the namespace, which are guaranteed to be
available during the call of the non-rcu protected function reg_vif_xmit
because of the interface reference which itself holds a reference to
the net namespace.

Fixes: f0ad0860d01e47 ("ipv4: ipmr: support multiple tables")
Fixes: d1db275dd3f6e4 ("ipv6: ip6mr: support multiple tables")
Reported-by: Bob Falken <NetFestivalHaveFun@gmx.com>
Cc: Patrick McHardy <kaber@trash.net>
Cc: Thomas Graf <tgraf@suug.ch>
Cc: Julian Anastasov <ja@ssi.bg>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 10 insertions, 4 deletions

diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
index 62212c772a4b..1672409f5ba5 100644
--- a/net/ipv4/ipmr.c
+++ b/net/ipv4/ipmr.c
@@ -157,9 +157,12 @@ static struct mr_table *ipmr_get_table(struct net *net, u32 id)
 static int ipmr_fib_lookup(struct net *net, struct flowi4 *flp4,
                            struct mr_table **mrt)
 {
-        struct ipmr_result res;
-        struct fib_lookup_arg arg = { .result = &res, };
         int err;
+        struct ipmr_result res;
+        struct fib_lookup_arg arg = {
+                .result = &res,
+                .flags = FIB_LOOKUP_NOREF,
+        };
 
         err = fib_rules_lookup(net->ipv4.mr_rules_ops,
                                flowi4_to_flowi(flp4), 0, &arg);
diff --git a/net/ipv6/ip6mr.c b/net/ipv6/ip6mr.c
index f365310bfcca..0eb4038a4d63 100644
--- a/net/ipv6/ip6mr.c
+++ b/net/ipv6/ip6mr.c
@@ -141,9 +141,12 @@ static struct mr6_table *ip6mr_get_table(struct net *net, u32 id)
 static int ip6mr_fib_lookup(struct net *net, struct flowi6 *flp6,
                             struct mr6_table **mrt)
 {
-        struct ip6mr_result res;
-        struct fib_lookup_arg arg = { .result = &res, };
         int err;
+        struct ip6mr_result res;
+        struct fib_lookup_arg arg = {
+                .result = &res,
+                .flags = FIB_LOOKUP_NOREF,
+        };
 
         err = fib_rules_lookup(net->ipv6.mr6_rules_ops,
                                flowi6_to_flowi(flp6), 0, &arg);