[PATCH 3.4 30/37] net: avoid reference counter overflows on fib_rules in multicast forwarding

From: Greg Kroah-Hartman
Date: Tue Feb 04 2014 - 18:13:59 EST

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


From: Hannes Frederic Sowa <hannes@xxxxxxxxxxxxxxxxxxx>

[ Upstream commit 95f4a45de1a0f172b35451fc52283290adb21f6e ]

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@xxxxxxx>
Cc: Patrick McHardy <kaber@xxxxxxxxx>
Cc: Thomas Graf <tgraf@xxxxxxx>
Cc: Julian Anastasov <ja@xxxxxx>
Cc: Eric Dumazet <eric.dumazet@xxxxxxxxx>
Signed-off-by: Hannes Frederic Sowa <hannes@xxxxxxxxxxxxxxxxxxx>
Acked-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
net/ipv4/ipmr.c | 7 +++++--
net/ipv6/ip6mr.c | 7 +++++--
2 files changed, 10 insertions(+), 4 deletions(-)

--- a/net/ipv4/ipmr.c
+++ b/net/ipv4/ipmr.c
@@ -154,9 +154,12 @@ static struct mr_table *ipmr_get_table(s
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);
--- a/net/ipv6/ip6mr.c
+++ b/net/ipv6/ip6mr.c
@@ -138,9 +138,12 @@ static struct mr6_table *ip6mr_get_table
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);

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