[PATCH 4.9 31/48] rtnetlink: make sure to refresh master_dev/m_ops in __rtnl_newlink()

Greg Kroah-Hartman
2022-02-07T11:13:58Z

From: Eric Dumazet <edumazet@google.com>

commit c6f6f2444bdbe0079e41914a35081530d0409963 upstream.

While looking at one unrelated syzbot bug, I found the replay logic
in __rtnl_newlink() to potentially trigger use-after-free.

It is better to clear master_dev and m_ops inside the loop,
in case we have to replay it.

Fixes: ba7d49b1f0f8 ("rtnetlink: provide api for getting and setting slave info")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Jiri Pirko <jiri@nvidia.com>
Link: https://lore.kernel.org/r/20220201012106.216495-1-eric.dumazet@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/core/rtnetlink.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -2454,9 +2454,9 @@ static int rtnl_newlink(struct sk_buff *
{
struct net *net = sock_net(skb->sk);
const struct rtnl_link_ops *ops;
- const struct rtnl_link_ops *m_ops = NULL;
+ const struct rtnl_link_ops *m_ops;
struct net_device *dev;
- struct net_device *master_dev = NULL;
+ struct net_device *master_dev;
struct ifinfomsg *ifm;
char kind[MODULE_NAME_LEN];
char ifname[IFNAMSIZ];
@@ -2487,6 +2487,8 @@ replay:
dev = NULL;
}

+ master_dev = NULL;
+ m_ops = NULL;
if (dev) {
master_dev = netdev_master_upper_dev_get(dev);
if (master_dev)