[Devel] [PATCH rh7] net: avoid reference counter overflows on fib_rules in multicast forwarding

[Stanislav Kinsburskiy]

Andrey, please review

23.11.2015 17:08, Stanislav Kinsburskiy пишет:
> From: Hannes Frederic Sowa <hannes at stressinduktion.org>
>
> 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.
>
> Backport: https://jira.sw.ru/browse/PSBM-41453
>
> Fixes: f0ad0860d01e47 ("ipv4: ipmr: support multiple tables")
> Fixes: d1db275dd3f6e4 ("ipv6: ip6mr: support multiple tables")
> Reported-by: Bob Falken <NetFestivalHaveFun at gmx.com>
> Cc: Patrick McHardy <kaber at trash.net>
> Cc: Thomas Graf <tgraf at suug.ch>
> Cc: Julian Anastasov <ja at ssi.bg>
> Cc: Eric Dumazet <eric.dumazet at gmail.com>
> Signed-off-by: Hannes Frederic Sowa <hannes at stressinduktion.org>
> Acked-by: Eric Dumazet <edumazet at google.com>
> Signed-off-by: David S. Miller <davem at davemloft.net>
> Signed-off-by: Stanislav Kinsburskiy <skinsbursky at odin.com>
> ---
>   net/ipv4/ipmr.c  |    7 +++++--
>   net/ipv6/ip6mr.c |    7 +++++--
>   2 files changed, 10 insertions(+), 4 deletions(-)
>
> diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
> index aa7bc00..4234b01 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 4b42124..9f44ebc 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);
>
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