Linux 5.12: ERROR: modpost: "find_module" [/var/lib/dkms/ipt-netflow/2.5.1/build/ipt_NETFLOW.ko] undefined!

[piso77]

Upstream has unexported find_module():

commit 089049f6c9956c5cf1fc89fe10229c76e99f4bef
Author: Christoph Hellwig <[email protected]>
Date:   Tue Feb 2 13:13:24 2021 +0100

    module: unexport find_module and module_mutex
    
    find_module is not used by modular code any more, and random driver code
    has no business calling it to start with.
    
    Reviewed-by: Miroslav Benes <[email protected]>
    Signed-off-by: Christoph Hellwig <[email protected]>
    Signed-off-by: Jessica Yu <[email protected]>

but i'm not entirely sure how to fix this -- ipt_NETFLOW.c::register_ct_events():

#if LINUX_VERSION_CODE < KERNEL_VERSION(3,2,0)
            !rcu_dereference(nf_conntrack_event_cb) ||
#endif
            !find_module(NETLINK_M)) {
                printk("Loading " NETLINK_M "\n");
                request_module(NETLINK_M);

        }
        /* Reference netlink module to prevent it's unsafe unload before us. */
        if (!netlink_m && (netlink_m = find_module(NETLINK_M))) {
#if LINUX_VERSION_CODE < KERNEL_VERSION(5,9,0)
                use_module(THIS_MODULE, netlink_m);
#else
                if (!try_module_get(netlink_m))
                        netlink_m = NULL;
#endif

[aabc]

Thanks for the report! I am working on it.