fib: use atomic_inc_not_zero() in fib_rules_lookup

It seems we dont use appropriate refcount increment in an
rcu_read_lock() protected section.

fib_rule_get() might increment a null refcount and bad things could
happen.

While fib_nl_delrule() respects an rcu grace period before calling
fib_rule_put(), fib_rules_cleanup_ops() calls fib_rule_put() without a
grace period.

Note : after this patch, we might avoid the synchronize_rcu() call done
in fib_nl_delrule()

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 5 insertions, 3 deletions

diff --git a/net/core/fib_rules.c b/net/core/fib_rules.c
index 42e84e08a1be..d0787284cb07 100644
--- a/net/core/fib_rules.c
+++ b/net/core/fib_rules.c
@@ -225,9 +225,11 @@ jumped:
                         err = ops->action(rule, fl, flags, arg);
 
                 if (err != -EAGAIN) {
-                        fib_rule_get(rule);
-                        arg->rule = rule;
-                        goto out;
+                        if (likely(atomic_inc_not_zero(&rule->refcnt))) {
+                                arg->rule = rule;
+                                goto out;
+                        }
+                        break;
                 }
         }