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    Subject[PATCH AUTOSEL 6.1 18/24] neigh: make sure used and confirmed times are valid
    Date
    From: Julian Anastasov <ja@ssi.bg>

    [ Upstream commit c1d2ecdf5e38e3489ce8328238b558b3b2866fe1 ]

    Entries can linger in cache without timer for days, thanks to
    the gc_thresh1 limit. As result, without traffic, the confirmed
    time can be outdated and to appear to be in the future. Later,
    on traffic, NUD_STALE entries can switch to NUD_DELAY and start
    the timer which can see the invalid confirmed time and wrongly
    switch to NUD_REACHABLE state instead of NUD_PROBE. As result,
    timer is set many days in the future. This is more visible on
    32-bit platforms, with higher HZ value.

    Why this is a problem? While we expect unused entries to expire,
    such entries stay in REACHABLE state for too long, locked in
    cache. They are not expired normally, only when cache is full.

    Problem and the wrong state change reported by Zhang Changzhong:

    172.16.1.18 dev bond0 lladdr 0a:0e:0f:01:12:01 ref 1 used 350521/15994171/350520 probes 4 REACHABLE

    350520 seconds have elapsed since this entry was last updated, but it is
    still in the REACHABLE state (base_reachable_time_ms is 30000),
    preventing lladdr from being updated through probe.

    Fix it by ensuring timer is started with valid used/confirmed
    times. Considering the valid time range is LONG_MAX jiffies,
    we try not to go too much in the past while we are in
    DELAY/PROBE state. There are also places that need
    used/updated times to be validated while timer is not running.

    Reported-by: Zhang Changzhong <zhangchangzhong@huawei.com>
    Signed-off-by: Julian Anastasov <ja@ssi.bg>
    Tested-by: Zhang Changzhong <zhangchangzhong@huawei.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    net/core/neighbour.c | 18 +++++++++++++++---
    1 file changed, 15 insertions(+), 3 deletions(-)

    diff --git a/net/core/neighbour.c b/net/core/neighbour.c
    index 952a54763358e..bf081f62ae58b 100644
    --- a/net/core/neighbour.c
    +++ b/net/core/neighbour.c
    @@ -269,7 +269,7 @@ static int neigh_forced_gc(struct neigh_table *tbl)
    (n->nud_state == NUD_NOARP) ||
    (tbl->is_multicast &&
    tbl->is_multicast(n->primary_key)) ||
    - time_after(tref, n->updated))
    + !time_in_range(n->updated, tref, jiffies))
    remove = true;
    write_unlock(&n->lock);

    @@ -289,7 +289,17 @@ static int neigh_forced_gc(struct neigh_table *tbl)

    static void neigh_add_timer(struct neighbour *n, unsigned long when)
    {
    + /* Use safe distance from the jiffies - LONG_MAX point while timer
    + * is running in DELAY/PROBE state but still show to user space
    + * large times in the past.
    + */
    + unsigned long mint = jiffies - (LONG_MAX - 86400 * HZ);
    +
    neigh_hold(n);
    + if (!time_in_range(n->confirmed, mint, jiffies))
    + n->confirmed = mint;
    + if (time_before(n->used, n->confirmed))
    + n->used = n->confirmed;
    if (unlikely(mod_timer(&n->timer, when))) {
    printk("NEIGH: BUG, double timer add, state is %x\n",
    n->nud_state);
    @@ -1001,12 +1011,14 @@ static void neigh_periodic_work(struct work_struct *work)
    goto next_elt;
    }

    - if (time_before(n->used, n->confirmed))
    + if (time_before(n->used, n->confirmed) &&
    + time_is_before_eq_jiffies(n->confirmed))
    n->used = n->confirmed;

    if (refcount_read(&n->refcnt) == 1 &&
    (state == NUD_FAILED ||
    - time_after(jiffies, n->used + NEIGH_VAR(n->parms, GC_STALETIME)))) {
    + !time_in_range_open(jiffies, n->used,
    + n->used + NEIGH_VAR(n->parms, GC_STALETIME)))) {
    *np = n->next;
    neigh_mark_dead(n);
    write_unlock(&n->lock);
    --
    2.39.0
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