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    Subject[PATCH 4.9 137/171] ipv6/ndisc: Preserve IPv6 control buffer if protocol error handlers are called
    Date
    4.9-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Stefano Brivio <sbrivio@redhat.com>

    [ Upstream commit ee1abcf689353f36d9322231b4320926096bdee0 ]

    Commit a61bbcf28a8c ("[NET]: Store skb->timestamp as offset to a base
    timestamp") introduces a neighbour control buffer and zeroes it out in
    ndisc_rcv(), as ndisc_recv_ns() uses it.

    Commit f2776ff04722 ("[IPV6]: Fix address/interface handling in UDP and
    DCCP, according to the scoping architecture.") introduces the usage of the
    IPv6 control buffer in protocol error handlers (e.g. inet6_iif() in
    present-day __udp6_lib_err()).

    Now, with commit b94f1c0904da ("ipv6: Use icmpv6_notify() to propagate
    redirect, instead of rt6_redirect()."), we call protocol error handlers
    from ndisc_redirect_rcv(), after the control buffer is already stolen and
    some parts are already zeroed out. This implies that inet6_iif() on this
    path will always return zero.

    This gives unexpected results on UDP socket lookup in __udp6_lib_err(), as
    we might actually need to match sockets for a given interface.

    Instead of always claiming the control buffer in ndisc_rcv(), do that only
    when needed.

    Fixes: b94f1c0904da ("ipv6: Use icmpv6_notify() to propagate redirect, instead of rt6_redirect().")
    Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
    Reviewed-by: Sabrina Dubroca <sd@queasysnail.net>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    net/ipv6/ndisc.c | 3 +--
    1 file changed, 1 insertion(+), 2 deletions(-)

    --- a/net/ipv6/ndisc.c
    +++ b/net/ipv6/ndisc.c
    @@ -1692,10 +1692,9 @@ int ndisc_rcv(struct sk_buff *skb)
    return 0;
    }

    - memset(NEIGH_CB(skb), 0, sizeof(struct neighbour_cb));
    -
    switch (msg->icmph.icmp6_type) {
    case NDISC_NEIGHBOUR_SOLICITATION:
    + memset(NEIGH_CB(skb), 0, sizeof(struct neighbour_cb));
    ndisc_recv_ns(skb);
    break;


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