[PATCH 4.9 092/117] ipv6: flowlabel: fl6_sock_lookup() must use atomic_inc_not_zero

[Greg Kroah-Hartman]

From: Eric Dumazet <eduma...@google.com>

[ Upstream commit 65a3c497c0e965a552008db8bc2653f62bc925a1 ]

Before taking a refcount, make sure the object is not already
scheduled for deletion.

Same fix is needed in ipv6_flowlabel_opt()

Fixes: 18367681a10b ("ipv6 flowlabel: Convert np->ipv6_fl_list to RCU.")
Signed-off-by: Eric Dumazet <eduma...@google.com>
Cc: Willem de Bruijn <will...@google.com>
Signed-off-by: David S. Miller <da...@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
 net/ipv6/ip6_flowlabel.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

--- a/net/ipv6/ip6_flowlabel.c
+++ b/net/ipv6/ip6_flowlabel.c
@@ -254,9 +254,9 @@ struct ip6_flowlabel *fl6_sock_lookup(st
        rcu_read_lock_bh();
        for_each_sk_fl_rcu(np, sfl) {
                struct ip6_flowlabel *fl = sfl->fl;
-               if (fl->label == label) {
+
+               if (fl->label == label && atomic_inc_not_zero(&fl->users)) {
                        fl->lastuse = jiffies;
-                       atomic_inc(&fl->users);
                        rcu_read_unlock_bh();
                        return fl;
                }
@@ -623,7 +623,8 @@ int ipv6_flowlabel_opt(struct sock *sk,
                                                goto done;
                                        }
                                        fl1 = sfl->fl;
-                                       atomic_inc(&fl1->users);
+                                       if (!atomic_inc_not_zero(&fl1->users))
+                                               fl1 = NULL;
                                        break;
                                }
                        }