linux-kernel - [PATCH 3.16 52/87] ipv6: flowlabel: fl6_sock_lookup() must use atomic_inc_not

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Message-ID: <lsq.1570043211.891718382@decadent.org.uk>
Date:   Wed, 02 Oct 2019 20:06:51 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "David S. Miller" <davem@...emloft.net>,
        "Eric Dumazet" <edumazet@...gle.com>,
        "Willem de Bruijn" <willemb@...gle.com>
Subject: [PATCH 3.16 52/87] ipv6: flowlabel: fl6_sock_lookup() must use
 atomic_inc_not_zero

3.16.75-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Dumazet <edumazet@...gle.com>

commit 65a3c497c0e965a552008db8bc2653f62bc925a1 upstream.

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 <edumazet@...gle.com>
Cc: Willem de Bruijn <willemb@...gle.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 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
@@ -255,9 +255,9 @@ struct ip6_flowlabel * fl6_sock_lookup(s
 	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;
 		}
@@ -619,7 +619,8 @@ 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;
 				}
 			}