ipv6/addrconf: ensure addrconf_verify_rtnl() has completed

Before freeing the hash table in addrconf_exit_net(),
we need to make sure the work queue has completed,
or risk NULL dereference or UAF.

Thus, use cancel_delayed_work_sync() to enforce this.
We do not hold RTNL in addrconf_exit_net(), making this safe.

Fixes: 8805d13ff1b2 ("ipv6/addrconf: use one delayed work per netns")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://lore.kernel.org/r/20220216182037.3742-1-eric.dumazet@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 57fbd6f..44e1647 100644 (file)
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -7187,7 +7187,7 @@ static void __net_exit addrconf_exit_net(struct net *net)
        kfree(net->ipv6.devconf_all);
        net->ipv6.devconf_all = NULL;
 
-       cancel_delayed_work(&net->ipv6.addr_chk_work);
+       cancel_delayed_work_sync(&net->ipv6.addr_chk_work);
        /*
         *      Check hash table, then free it.
         */