From: Vlad Buslov <vladbu@mellanox.com>
Date: Fri, 10 Dec 2021 10:47:25 +0000 (+0000)
Subject: net: core: netlink: add helper refcount dec and lock function
X-Git-Tag: v4.19.221~64
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=cd25f1099284a0cbe916344fc1e6c1ffed6c5306;p=thirdparty%2Fkernel%2Fstable.git

net: core: netlink: add helper refcount dec and lock function

[ Upstream commit 6f99528e9797794b91b43321fbbc93fe772b0803 ]

Rtnl lock is encapsulated in netlink and cannot be accessed by other
modules directly. This means that reference counted objects that rely on
rtnl lock cannot use it with refcounter helper function that atomically
releases decrements reference and obtains mutex.

This patch implements simple wrapper function around refcount_dec_and_lock
that obtains rtnl lock if reference counter value reached 0.

Signed-off-by: Vlad Buslov <vladbu@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[Lee: Sent to Stable]
Link: https://syzkaller.appspot.com/bug?id=d7e411c5472dd5da33d8cc921ccadc747743a568
Reported-by: syzbot+5f229e48cccc804062c0@syzkaller.appspotmail.com
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/include/linux/rtnetlink.h b/include/linux/rtnetlink.h
index 5225832bd6ff1..9cdd76348d9ab 100644
--- a/include/linux/rtnetlink.h
+++ b/include/linux/rtnetlink.h
@@ -6,6 +6,7 @@
 #include <linux/mutex.h>
 #include <linux/netdevice.h>
 #include <linux/wait.h>
+#include <linux/refcount.h>
 #include <uapi/linux/rtnetlink.h>
 
 extern int rtnetlink_send(struct sk_buff *skb, struct net *net, u32 pid, u32 group, int echo);
@@ -34,6 +35,7 @@ extern void rtnl_unlock(void);
 extern int rtnl_trylock(void);
 extern int rtnl_is_locked(void);
 extern int rtnl_lock_killable(void);
+extern bool refcount_dec_and_rtnl_lock(refcount_t *r);
 
 extern wait_queue_head_t netdev_unregistering_wq;
 extern struct rw_semaphore pernet_ops_rwsem;
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 83de32e34bb55..907dd0c7e8a66 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -130,6 +130,12 @@ int rtnl_is_locked(void)
 }
 EXPORT_SYMBOL(rtnl_is_locked);
 
+bool refcount_dec_and_rtnl_lock(refcount_t *r)
+{
+	return refcount_dec_and_mutex_lock(r, &rtnl_mutex);
+}
+EXPORT_SYMBOL(refcount_dec_and_rtnl_lock);
+
 #ifdef CONFIG_PROVE_LOCKING
 bool lockdep_rtnl_is_held(void)
 {