From: Eric Dumazet <edumazet@google.com> stable inclusion from linux-4.19.228 commit a01e60a1ec6bef9be471fb7182a33c6d6f124e93 -------------------------------- 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> Signed-off-by: Yongqiang Liu <liuyongqiang13@huawei.com> Signed-off-by: Laibin Qiu <qiulaibin@huawei.com> --- net/core/rtnetlink.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c index 83de32e34bb5..6cd0dbe42baa 100644 --- a/net/core/rtnetlink.c +++ b/net/core/rtnetlink.c @@ -2936,9 +2936,9 @@ static int rtnl_newlink(struct sk_buff *skb, struct nlmsghdr *nlh, { 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]; @@ -2973,6 +2973,8 @@ static int rtnl_newlink(struct sk_buff *skb, struct nlmsghdr *nlh, dev = NULL; } + master_dev = NULL; + m_ops = NULL; if (dev) { master_dev = netdev_master_upper_dev_get(dev); if (master_dev) -- 2.22.0