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    Subject[PATCH 4.19 446/639] ip6_fib: Dont discard nodes with valid routing information in fib6_locate_1()
    Date
    From: Stefano Brivio <sbrivio@redhat.com>

    [ Upstream commit 40cb35d5dc04e7f89cbc7b1fc9b4b48d9f1e5343 ]

    When we perform an inexact match on FIB nodes via fib6_locate_1(), longer
    prefixes will be preferred to shorter ones. However, it might happen that
    a node, with higher fn_bit value than some other, has no valid routing
    information.

    In this case, we'll pick that node, but it will be discarded by the check
    on RTN_RTINFO in fib6_locate(), and we might miss nodes with valid routing
    information but with lower fn_bit value.

    This is apparent when a routing exception is created for a default route:
    # ip -6 route list
    fc00:1::/64 dev veth_A-R1 proto kernel metric 256 pref medium
    fc00:2::/64 dev veth_A-R2 proto kernel metric 256 pref medium
    fc00:4::1 via fc00:2::2 dev veth_A-R2 metric 1024 pref medium
    fe80::/64 dev veth_A-R1 proto kernel metric 256 pref medium
    fe80::/64 dev veth_A-R2 proto kernel metric 256 pref medium
    default via fc00:1::2 dev veth_A-R1 metric 1024 pref medium
    # ip -6 route list cache
    fc00:4::1 via fc00:2::2 dev veth_A-R2 metric 1024 expires 593sec mtu 1500 pref medium
    fc00:3::1 via fc00:1::2 dev veth_A-R1 metric 1024 expires 593sec mtu 1500 pref medium
    # ip -6 route flush cache # node for default route is discarded
    Failed to send flush request: No such process
    # ip -6 route list cache
    fc00:3::1 via fc00:1::2 dev veth_A-R1 metric 1024 expires 586sec mtu 1500 pref medium

    Check right away if the node has a RTN_RTINFO flag, before replacing the
    'prev' pointer, that indicates the longest matching prefix found so far.

    Fixes: 38fbeeeeccdb ("ipv6: prepare fib6_locate() for exception table")
    Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    net/ipv6/ip6_fib.c | 3 ++-
    1 file changed, 2 insertions(+), 1 deletion(-)

    diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
    index bbb5ffb3397d8..7091568b9f630 100644
    --- a/net/ipv6/ip6_fib.c
    +++ b/net/ipv6/ip6_fib.c
    @@ -1529,7 +1529,8 @@ static struct fib6_node *fib6_locate_1(struct fib6_node *root,
    if (plen == fn->fn_bit)
    return fn;

    - prev = fn;
    + if (fn->fn_flags & RTN_RTINFO)
    + prev = fn;

    next:
    /*
    --
    2.20.1


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