netdev - Re: [PATCH v2] ipv6: do not free rt if FIB_LOOKUP

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Date:   Tue, 24 Sep 2019 10:02:42 -0700
From:   Wei Wang <weiwan@...gle.com>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        "David S . Miller" <davem@...emloft.net>, stable@...r.kernel.org
Subject: Re: [PATCH v2] ipv6: do not free rt if FIB_LOOKUP_NOREF is set on
 suppress rule

On Tue, Sep 24, 2019 at 7:01 AM Jason A. Donenfeld <Jason@...c4.com> wrote:
>
> Commit 7d9e5f422150 removed references from certain dsts, but accounting
> for this never translated down into the fib6 suppression code. This bug
> was triggered by WireGuard users who use wg-quick(8), which uses the
> "suppress-prefix" directive to ip-rule(8) for routing all of their
> internet traffic without routing loops. The test case added here
> causes the reference underflow by causing packets to evaluate a suppress
> rule.
>
> Cc: stable@...r.kernel.org
> Fixes: 7d9e5f422150 ("ipv6: convert major tx path to use RT6_LOOKUP_F_DST_NOREF")
> Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
> ---
Acked-by: Wei Wang <weiwan@...gle.com>

Good catch. Thanks for the fix.

>  net/ipv6/fib6_rules.c                    |  3 ++-
>  tools/testing/selftests/net/fib_tests.sh | 17 ++++++++++++++++-
>  2 files changed, 18 insertions(+), 2 deletions(-)
>
> diff --git a/net/ipv6/fib6_rules.c b/net/ipv6/fib6_rules.c
> index d22b6c140f23..f9e8fe3ff0c5 100644
> --- a/net/ipv6/fib6_rules.c
> +++ b/net/ipv6/fib6_rules.c
> @@ -287,7 +287,8 @@ static bool fib6_rule_suppress(struct fib_rule *rule, struct fib_lookup_arg *arg
>         return false;
>
>  suppress_route:
> -       ip6_rt_put(rt);
> +       if (!(arg->flags & FIB_LOOKUP_NOREF))
> +               ip6_rt_put(rt);
>         return true;
>  }
>
> diff --git a/tools/testing/selftests/net/fib_tests.sh b/tools/testing/selftests/net/fib_tests.sh
> index 4465fc2dae14..c2c5f2bf0f95 100755
> --- a/tools/testing/selftests/net/fib_tests.sh
> +++ b/tools/testing/selftests/net/fib_tests.sh
> @@ -9,7 +9,7 @@ ret=0
>  ksft_skip=4
>
>  # all tests in this script. Can be overridden with -t option
> -TESTS="unregister down carrier nexthop ipv6_rt ipv4_rt ipv6_addr_metric ipv4_addr_metric ipv6_route_metrics ipv4_route_metrics ipv4_route_v6_gw rp_filter"
> +TESTS="unregister down carrier nexthop suppress ipv6_rt ipv4_rt ipv6_addr_metric ipv4_addr_metric ipv6_route_metrics ipv4_route_metrics ipv4_route_v6_gw rp_filter"
>
>  VERBOSE=0
>  PAUSE_ON_FAIL=no
> @@ -614,6 +614,20 @@ fib_nexthop_test()
>         cleanup
>  }
>
> +fib_suppress_test()
> +{
> +       $IP link add dummy1 type dummy
> +       $IP link set dummy1 up
> +       $IP -6 route add default dev dummy1
> +       $IP -6 rule add table main suppress_prefixlength 0
> +       ping -f -c 1000 -W 1 1234::1 || true
> +       $IP -6 rule del table main suppress_prefixlength 0
> +       $IP link del dummy1
> +
> +       # If we got here without crashing, we're good.
> +       return 0
> +}
> +
>  ################################################################################
>  # Tests on route add and replace
>
> @@ -1591,6 +1605,7 @@ do
>         fib_carrier_test|carrier)       fib_carrier_test;;
>         fib_rp_filter_test|rp_filter)   fib_rp_filter_test;;
>         fib_nexthop_test|nexthop)       fib_nexthop_test;;
> +       fib_suppress_test|suppress)     fib_suppress_test;;
>         ipv6_route_test|ipv6_rt)        ipv6_route_test;;
>         ipv4_route_test|ipv4_rt)        ipv4_route_test;;
>         ipv6_addr_metric)               ipv6_addr_metric_test;;
> --
> 2.21.0
>