• Stephen Suryaputra Lin's avatar
    ipv4: use new_gw for redirect neigh lookup · ae9e052a
    Stephen Suryaputra Lin authored
    [ Upstream commit 969447f2 ]
    
    In v2.6, ip_rt_redirect() calls arp_bind_neighbour() which returns 0
    and then the state of the neigh for the new_gw is checked. If the state
    isn't valid then the redirected route is deleted. This behavior is
    maintained up to v3.5.7 by check_peer_redirect() because rt->rt_gateway
    is assigned to peer->redirect_learned.a4 before calling
    ipv4_neigh_lookup().
    
    After commit 5943634f ("ipv4: Maintain redirect and PMTU info in
    struct rtable again."), ipv4_neigh_lookup() is performed without the
    rt_gateway assigned to the new_gw. In the case when rt_gateway (old_gw)
    isn't zero, the function uses it as the key. The neigh is most likely
    valid since the old_gw is the one that sends the ICMP redirect message.
    Then the new_gw is assigned to fib_nh_exception. The problem is: the
    new_gw ARP may never gets resolved and the traffic is blackholed.
    
    So, use the new_gw for neigh lookup.
    
    Changes from v1:
     - use __ipv4_neigh_lookup instead (per Eric Dumazet).
    
    Fixes: 5943634f ("ipv4: Maintain redirect and PMTU info in struct rtable again.")
    Signed-off-by: default avatarStephen Suryaputra Lin <ssurya@ieee.org>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    ae9e052a
route.c 71 KB