From: Eric Dumazet <edumazet@xxxxxxxxxx> 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@xxxxxxxxxx> Cc: Jiri Pirko <jiri@xxxxxxxxxx> Link: https://lore.kernel.org/r/20220201012106.216495-1-eric.dumazet@xxxxxxxxx Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- 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) Patches currently in stable-queue which might be from edumazet@xxxxxxxxxx are queue-4.9/ipv4-avoid-using-shared-ip-generator-for-connected-sockets.patch queue-4.9/ipv4-tcp-send-zero-ipid-in-synack-messages.patch queue-4.9/rtnetlink-make-sure-to-refresh-master_dev-m_ops-in-__rtnl_newlink.patch queue-4.9/ipv4-raw-lock-the-socket-in-raw_bind.patch queue-4.9/af_packet-fix-data-race-in-packet_setsockopt-packet_setsockopt.patch