[PATCH v2 net] ipv6: flowlabel: fl6_sock_lookup() must use atomic_inc_not_zero

[Eric Dumazet]

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>
---
 net/ipv6/ip6_flowlabel.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/net/ipv6/ip6_flowlabel.c b/net/ipv6/ip6_flowlabel.c
index 
be5f3d7ceb966d609121f89a6cc5dcc605834c89..f994f50e1516226c88101f901f71647514ad580b
 100644
--- a/net/ipv6/ip6_flowlabel.c
+++ b/net/ipv6/ip6_flowlabel.c
@@ -254,9 +254,9 @@ struct ip6_flowlabel *fl6_sock_lookup(struct sock *sk, 
__be32 label)
        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;
                }
@@ -622,7 +622,8 @@ int ipv6_flowlabel_opt(struct sock *sk, char __user 
*optval, int optlen)
                                                goto done;
                                        }
                                        fl1 = sfl->fl;
-                                       atomic_inc(&fl1->users);
+                                       if (!atomic_inc_not_zero(&fl1->users))
+                                               fl1 = NULL;
                                        break;
                                }
                        }
-- 
2.22.0.rc1.311.g5d7573a151-goog