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    Subject[PATCH 3.19.y-ckt 006/251] neigh: do not modify unlinked entries
    Date
    3.19.8-ckt4 -stable review patch.  If anyone has any objections, please let me know.

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

    From: Julian Anastasov <ja@ssi.bg>

    [ Upstream commit 2c51a97f76d20ebf1f50fef908b986cb051fdff9 ]

    The lockless lookups can return entry that is unlinked.
    Sometimes they get reference before last neigh_cleanup_and_release,
    sometimes they do not need reference. Later, any
    modification attempts may result in the following problems:

    1. entry is not destroyed immediately because neigh_update
    can start the timer for dead entry, eg. on change to NUD_REACHABLE
    state. As result, entry lives for some time but is invisible
    and out of control.

    2. __neigh_event_send can run in parallel with neigh_destroy
    while refcnt=0 but if timer is started and expired refcnt can
    reach 0 for second time leading to second neigh_destroy and
    possible crash.

    Thanks to Eric Dumazet and Ying Xue for their work and analyze
    on the __neigh_event_send change.

    Fixes: 767e97e1e0db ("neigh: RCU conversion of struct neighbour")
    Fixes: a263b3093641 ("ipv4: Make neigh lookups directly in output packet path.")
    Fixes: 6fd6ce2056de ("ipv6: Do not depend on rt->n in ip6_finish_output2().")
    Cc: Eric Dumazet <eric.dumazet@gmail.com>
    Cc: Ying Xue <ying.xue@windriver.com>
    Signed-off-by: Julian Anastasov <ja@ssi.bg>
    Acked-by: Eric Dumazet <edumazet@google.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Kamal Mostafa <kamal@canonical.com>
    ---
    net/core/neighbour.c | 13 +++++++++++++
    1 file changed, 13 insertions(+)

    diff --git a/net/core/neighbour.c b/net/core/neighbour.c
    index 8d614c9..0385351 100644
    --- a/net/core/neighbour.c
    +++ b/net/core/neighbour.c
    @@ -971,6 +971,8 @@ int __neigh_event_send(struct neighbour *neigh, struct sk_buff *skb)
    rc = 0;
    if (neigh->nud_state & (NUD_CONNECTED | NUD_DELAY | NUD_PROBE))
    goto out_unlock_bh;
    + if (neigh->dead)
    + goto out_dead;

    if (!(neigh->nud_state & (NUD_STALE | NUD_INCOMPLETE))) {
    if (NEIGH_VAR(neigh->parms, MCAST_PROBES) +
    @@ -1027,6 +1029,13 @@ out_unlock_bh:
    write_unlock(&neigh->lock);
    local_bh_enable();
    return rc;
    +
    +out_dead:
    + if (neigh->nud_state & NUD_STALE)
    + goto out_unlock_bh;
    + write_unlock_bh(&neigh->lock);
    + kfree_skb(skb);
    + return 1;
    }
    EXPORT_SYMBOL(__neigh_event_send);

    @@ -1090,6 +1099,8 @@ int neigh_update(struct neighbour *neigh, const u8 *lladdr, u8 new,
    if (!(flags & NEIGH_UPDATE_F_ADMIN) &&
    (old & (NUD_NOARP | NUD_PERMANENT)))
    goto out;
    + if (neigh->dead)
    + goto out;

    if (!(new & NUD_VALID)) {
    neigh_del_timer(neigh);
    @@ -1239,6 +1250,8 @@ EXPORT_SYMBOL(neigh_update);
    */
    void __neigh_set_probe_once(struct neighbour *neigh)
    {
    + if (neigh->dead)
    + return;
    neigh->updated = jiffies;
    if (!(neigh->nud_state & NUD_FAILED))
    return;
    --
    1.9.1


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