I have Fedora 26 and build fails with kernel-4.12.13-300.fc26.x86_64. kernel-devel is installed as well.

Thanks
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make

gcc -c -o build/relay_pop.o src/relay_pop.c
gcc -o relay_pop build/relay_pop.o
make -C /lib/modules/4.12.13-300.fc26.x86_64/build M=/root/git/TorProxy/build/kernel_module modules
make[1]: Entering directory '/usr/src/kernels/4.12.13-300.fc26.x86_64'
CC [M] /root/git/TorProxy/build/kernel_module/torproxy_module.o
/root/git/TorProxy/build/kernel_module/torproxy_module.c: In function ‘local_out_hook_func’:
/root/git/TorProxy/build/kernel_module/torproxy_module.c:200:32: error: passing argument 1 of ‘ip_route_me_harder’ from incompatible pointer type [-Werror=incompatible-pointer-types]
err = ip_route_me_harder(skb, RTN_UNSPEC);
^~~
In file included from /root/git/TorProxy/build/kernel_module/torproxy_module.c:17:0:
./include/linux/netfilter_ipv4.h:9:5: note: expected ‘struct net *’ but argument is of type ‘struct sk_buff *’
int ip_route_me_harder(struct net *net, struct sk_buff *skb, unsigned addr_type);
^~~~~~~~~~~~~~~~~~
/root/git/TorProxy/build/kernel_module/torproxy_module.c:200:13: error: too few arguments to function ‘ip_route_me_harder’
err = ip_route_me_harder(skb, RTN_UNSPEC);
^~~~~~~~~~~~~~~~~~
In file included from /root/git/TorProxy/build/kernel_module/torproxy_module.c:17:0:
./include/linux/netfilter_ipv4.h:9:5: note: declared here
int ip_route_me_harder(struct net *net, struct sk_buff *skb, unsigned addr_type);
^~~~~~~~~~~~~~~~~~
/root/git/TorProxy/build/kernel_module/torproxy_module.c:257:32: error: passing argument 1 of ‘ip_route_me_harder’ from incompatible pointer type [-Werror=incompatible-pointer-types]
err = ip_route_me_harder(skb, RTN_UNSPEC);
^~~
In file included from /root/git/TorProxy/build/kernel_module/torproxy_module.c:17:0:
./include/linux/netfilter_ipv4.h:9:5: note: expected ‘struct net *’ but argument is of type ‘struct sk_buff *’
int ip_route_me_harder(struct net *net, struct sk_buff *skb, unsigned addr_type);
^~~~~~~~~~~~~~~~~~
/root/git/TorProxy/build/kernel_module/torproxy_module.c:257:13: error: too few arguments to function ‘ip_route_me_harder’
err = ip_route_me_harder(skb, RTN_UNSPEC);
^~~~~~~~~~~~~~~~~~
In file included from /root/git/TorProxy/build/kernel_module/torproxy_module.c:17:0:
./include/linux/netfilter_ipv4.h:9:5: note: declared here
int ip_route_me_harder(struct net *net, struct sk_buff *skb, unsigned addr_type);
^~~~~~~~~~~~~~~~~~
cc1: some warnings being treated as errors
make[2]: *** [scripts/Makefile.build:309: /root/git/TorProxy/build/kernel_module/torproxy_module.o] Error 1
make[1]: *** [Makefile:1519: module/root/git/TorProxy/build/kernel_module] Error 2
make[1]: Leaving directory '/usr/src/kernels/4.12.13-300.fc26.x86_64'
make: *** [Makefile:26: torproxy_module.o] Error 2