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d2ba09c17a
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 <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
43 lines
1.1 KiB
C
43 lines
1.1 KiB
C
// SPDX-License-Identifier: GPL-2.0
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#include <linux/uaccess.h>
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#include <linux/bpfilter.h>
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#include <uapi/linux/bpf.h>
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#include <linux/wait.h>
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#include <linux/kmod.h>
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int (*bpfilter_process_sockopt)(struct sock *sk, int optname,
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char __user *optval,
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unsigned int optlen, bool is_set);
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EXPORT_SYMBOL_GPL(bpfilter_process_sockopt);
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int bpfilter_mbox_request(struct sock *sk, int optname, char __user *optval,
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unsigned int optlen, bool is_set)
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{
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if (!bpfilter_process_sockopt) {
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int err = request_module("bpfilter");
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if (err)
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return err;
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if (!bpfilter_process_sockopt)
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return -ECHILD;
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}
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return bpfilter_process_sockopt(sk, optname, optval, optlen, is_set);
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}
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int bpfilter_ip_set_sockopt(struct sock *sk, int optname, char __user *optval,
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unsigned int optlen)
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{
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return bpfilter_mbox_request(sk, optname, optval, optlen, true);
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}
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int bpfilter_ip_get_sockopt(struct sock *sk, int optname, char __user *optval,
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int __user *optlen)
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{
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int len;
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if (get_user(len, optlen))
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return -EFAULT;
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return bpfilter_mbox_request(sk, optname, optval, len, false);
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}
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