From d2ba09c17a0647f899d6c20a11bab9e6d3382f07 Mon Sep 17 00:00:00 2001 From: Alexei Starovoitov Date: Mon, 21 May 2018 19:22:30 -0700 Subject: net: add skeleton of bpfilter kernel module bpfilter.ko consists of bpfilter_kern.c (normal kernel module code) and user mode helper code that is embedded into bpfilter.ko The steps to build bpfilter.ko are the following: - main.c is compiled by HOSTCC into the bpfilter_umh elf executable file - with quite a bit of objcopy and Makefile magic the bpfilter_umh elf file is converted into bpfilter_umh.o object file with _binary_net_bpfilter_bpfilter_umh_start and _end symbols Example: $ nm ./bld_x64/net/bpfilter/bpfilter_umh.o 0000000000004cf8 T _binary_net_bpfilter_bpfilter_umh_end 0000000000004cf8 A _binary_net_bpfilter_bpfilter_umh_size 0000000000000000 T _binary_net_bpfilter_bpfilter_umh_start - bpfilter_umh.o and bpfilter_kern.o are linked together into bpfilter.ko bpfilter_kern.c is a normal kernel module code that calls the fork_usermode_blob() helper to execute part of its own data as a user mode process. Notice that _binary_net_bpfilter_bpfilter_umh_start - end is placed into .init.rodata section, so it's freed as soon as __init function of bpfilter.ko is finished. As part of __init the bpfilter.ko does first request/reply action via two unix pipe provided by fork_usermode_blob() helper to make sure that umh is healthy. If not it will kill it via pid. Later bpfilter_process_sockopt() will be called from bpfilter hooks in get/setsockopt() to pass iptable commands into umh via bpfilter.ko If admin does 'rmmod bpfilter' the __exit code bpfilter.ko will kill umh as well. Signed-off-by: Alexei Starovoitov Signed-off-by: David S. Miller --- net/ipv4/bpfilter/Makefile | 2 ++ net/ipv4/bpfilter/sockopt.c | 42 ++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 44 insertions(+) create mode 100644 net/ipv4/bpfilter/Makefile create mode 100644 net/ipv4/bpfilter/sockopt.c (limited to 'net/ipv4/bpfilter') diff --git a/net/ipv4/bpfilter/Makefile b/net/ipv4/bpfilter/Makefile new file mode 100644 index 000000000000..ce262d76cc48 --- /dev/null +++ b/net/ipv4/bpfilter/Makefile @@ -0,0 +1,2 @@ +obj-$(CONFIG_BPFILTER) += sockopt.o + diff --git a/net/ipv4/bpfilter/sockopt.c b/net/ipv4/bpfilter/sockopt.c new file mode 100644 index 000000000000..42a96d2d8d05 --- /dev/null +++ b/net/ipv4/bpfilter/sockopt.c @@ -0,0 +1,42 @@ +// SPDX-License-Identifier: GPL-2.0 +#include +#include +#include +#include +#include + +int (*bpfilter_process_sockopt)(struct sock *sk, int optname, + char __user *optval, + unsigned int optlen, bool is_set); +EXPORT_SYMBOL_GPL(bpfilter_process_sockopt); + +int bpfilter_mbox_request(struct sock *sk, int optname, char __user *optval, + unsigned int optlen, bool is_set) +{ + if (!bpfilter_process_sockopt) { + int err = request_module("bpfilter"); + + if (err) + return err; + if (!bpfilter_process_sockopt) + return -ECHILD; + } + return bpfilter_process_sockopt(sk, optname, optval, optlen, is_set); +} + +int bpfilter_ip_set_sockopt(struct sock *sk, int optname, char __user *optval, + unsigned int optlen) +{ + return bpfilter_mbox_request(sk, optname, optval, optlen, true); +} + +int bpfilter_ip_get_sockopt(struct sock *sk, int optname, char __user *optval, + int __user *optlen) +{ + int len; + + if (get_user(len, optlen)) + return -EFAULT; + + return bpfilter_mbox_request(sk, optname, optval, len, false); +} -- cgit v1.2.3-59-g8ed1b