net: fix possible store tearing in neigh_periodic_work()

While looking at a related syzbot report involving neigh_periodic_work(),
I found that I forgot to add an annotation when deleting an
RCU protected item from a list.

Readers use rcu_deference(*np), we need to use either
rcu_assign_pointer() or WRITE_ONCE() on writer side
to prevent store tearing.

I use rcu_assign_pointer() to have lockdep support,
this was the choice made in neigh_flush_dev().

Fixes: 767e97e1e0db ("neigh: RCU conversion of struct neighbour")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 6b76cd103195374f73786b7bb94fb2f4051a3c73..7212c7e521ef6388f450f3882077e26088bb3644 100644 (file)
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -988,7 +988,9 @@ static void neigh_periodic_work(struct work_struct *work)
                            (state == NUD_FAILED ||
                             !time_in_range_open(jiffies, n->used,
                                                 n->used + NEIGH_VAR(n->parms, GC_STALETIME)))) {
-                               *np = n->next;
+                               rcu_assign_pointer(*np,
+                                       rcu_dereference_protected(n->next,
+                                               lockdep_is_held(&tbl->lock)));
                                neigh_mark_dead(n);
                                write_unlock(&n->lock);
                                neigh_cleanup_and_release(n);