Commit 63617421 authored Nov 22, 2012 by Julian Anastasov Committed by David S. Miller Nov 22, 2012

ipv4: do not cache looped multicasts



	Starting from 3.6 we cache output routes for
multicasts only when using route to 224/4. For local receivers
we can set RTCF_LOCAL flag depending on the membership but
in such case we use maddr and saddr which are not caching
keys as before. Additionally, we can not use same place to
cache routes that differ in RTCF_LOCAL flag value.

	Fix it by caching only RTCF_MULTICAST entries
without RTCF_LOCAL (send-only, no loopback). As a side effect,
we avoid unneeded lookup for fnhe when not caching because
multicasts are not redirected and they do not learn PMTU.

	Thanks to Maxime Bizon for showing the caching
problems in __mkroute_output for 3.6 kernels: different
RTCF_LOCAL flag in cache can lead to wrong ip_mc_output or
ip_output call and the visible problem is that traffic can
not reach local receivers via loopback.

Reported-by: Maxime Bizon <mbizon@freebox.fr>
Tested-by: Maxime Bizon <mbizon@freebox.fr>
Signed-off-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 84ec95b0

net/ipv4/route.c

+5 −2

Original line number	Diff line number	Diff line
		@@ -1785,6 +1785,7 @@ static struct rtable __mkroute_output(const struct fib_result res,
		if (dev_out->flags & IFF_LOOPBACK)
		flags \|= RTCF_LOCAL;

		do_cache = true;
		if (type == RTN_BROADCAST) {
		flags \|= RTCF_BROADCAST \| RTCF_LOCAL;
		fi = NULL;
		@@ -1793,6 +1794,8 @@ static struct rtable __mkroute_output(const struct fib_result res,
		if (!ip_check_mc_rcu(in_dev, fl4->daddr, fl4->saddr,
		fl4->flowi4_proto))
		flags &= ~RTCF_LOCAL;
		else
		do_cache = false;
		/* If multicast route do not exist use
		* default one, but do not gateway in this case.
		* Yes, it is hack.
		@@ -1802,8 +1805,8 @@ static struct rtable __mkroute_output(const struct fib_result res,
		}

		fnhe = NULL;
		do_cache = fi != NULL;
		if (fi) {
		do_cache &= fi != NULL;
		if (do_cache) {
		struct rtable __rcu **prth;
		struct fib_nh nh = &FIB_RES_NH(res);

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