Commit d2ba09c1 authored by Alexei Starovoitov's avatar Alexei Starovoitov Committed by David S. Miller

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: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 449325b5
/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _LINUX_BPFILTER_H
#define _LINUX_BPFILTER_H
#include <uapi/linux/bpfilter.h>
struct sock;
int bpfilter_ip_set_sockopt(struct sock *sk, int optname, char *optval,
unsigned int optlen);
int bpfilter_ip_get_sockopt(struct sock *sk, int optname, char *optval,
int *optlen);
extern int (*bpfilter_process_sockopt)(struct sock *sk, int optname,
char __user *optval,
unsigned int optlen, bool is_set);
#endif
/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _UAPI_LINUX_BPFILTER_H
#define _UAPI_LINUX_BPFILTER_H
#include <linux/if.h>
enum {
BPFILTER_IPT_SO_SET_REPLACE = 64,
BPFILTER_IPT_SO_SET_ADD_COUNTERS = 65,
BPFILTER_IPT_SET_MAX,
};
enum {
BPFILTER_IPT_SO_GET_INFO = 64,
BPFILTER_IPT_SO_GET_ENTRIES = 65,
BPFILTER_IPT_SO_GET_REVISION_MATCH = 66,
BPFILTER_IPT_SO_GET_REVISION_TARGET = 67,
BPFILTER_IPT_GET_MAX,
};
#endif /* _UAPI_LINUX_BPFILTER_H */
......@@ -202,6 +202,8 @@ source "net/bridge/netfilter/Kconfig"
endif
source "net/bpfilter/Kconfig"
source "net/dccp/Kconfig"
source "net/sctp/Kconfig"
source "net/rds/Kconfig"
......
......@@ -20,6 +20,7 @@ obj-$(CONFIG_TLS) += tls/
obj-$(CONFIG_XFRM) += xfrm/
obj-$(CONFIG_UNIX) += unix/
obj-$(CONFIG_NET) += ipv6/
obj-$(CONFIG_BPFILTER) += bpfilter/
obj-$(CONFIG_PACKET) += packet/
obj-$(CONFIG_NET_KEY) += key/
obj-$(CONFIG_BRIDGE) += bridge/
......
menuconfig BPFILTER
bool "BPF based packet filtering framework (BPFILTER)"
default n
depends on NET && BPF
help
This builds experimental bpfilter framework that is aiming to
provide netfilter compatible functionality via BPF
if BPFILTER
config BPFILTER_UMH
tristate "bpfilter kernel module with user mode helper"
default m
help
This builds bpfilter kernel module with embedded user mode helper
endif
# SPDX-License-Identifier: GPL-2.0
#
# Makefile for the Linux BPFILTER layer.
#
hostprogs-y := bpfilter_umh
bpfilter_umh-objs := main.o
HOSTCFLAGS += -I. -Itools/include/
ifeq ($(CONFIG_BPFILTER_UMH), y)
# builtin bpfilter_umh should be compiled with -static
# since rootfs isn't mounted at the time of __init
# function is called and do_execv won't find elf interpreter
HOSTLDFLAGS += -static
endif
# a bit of elf magic to convert bpfilter_umh binary into a binary blob
# inside bpfilter_umh.o elf file referenced by
# _binary_net_bpfilter_bpfilter_umh_start symbol
# which bpfilter_kern.c passes further into umh blob loader at run-time
quiet_cmd_copy_umh = GEN $@
cmd_copy_umh = echo ':' > $(obj)/.bpfilter_umh.o.cmd; \
$(OBJCOPY) -I binary -O $(CONFIG_OUTPUT_FORMAT) \
-B `$(OBJDUMP) -f $<|grep architecture|cut -d, -f1|cut -d' ' -f2` \
--rename-section .data=.init.rodata $< $@
$(obj)/bpfilter_umh.o: $(obj)/bpfilter_umh
$(call cmd,copy_umh)
obj-$(CONFIG_BPFILTER_UMH) += bpfilter.o
bpfilter-objs += bpfilter_kern.o bpfilter_umh.o
// SPDX-License-Identifier: GPL-2.0
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/init.h>
#include <linux/module.h>
#include <linux/umh.h>
#include <linux/bpfilter.h>
#include <linux/sched.h>
#include <linux/sched/signal.h>
#include <linux/fs.h>
#include <linux/file.h>
#include "msgfmt.h"
#define UMH_start _binary_net_bpfilter_bpfilter_umh_start
#define UMH_end _binary_net_bpfilter_bpfilter_umh_end
extern char UMH_start;
extern char UMH_end;
static struct umh_info info;
/* since ip_getsockopt() can run in parallel, serialize access to umh */
static DEFINE_MUTEX(bpfilter_lock);
static void shutdown_umh(struct umh_info *info)
{
struct task_struct *tsk;
tsk = pid_task(find_vpid(info->pid), PIDTYPE_PID);
if (tsk)
force_sig(SIGKILL, tsk);
fput(info->pipe_to_umh);
fput(info->pipe_from_umh);
}
static void __stop_umh(void)
{
if (bpfilter_process_sockopt) {
bpfilter_process_sockopt = NULL;
shutdown_umh(&info);
}
}
static void stop_umh(void)
{
mutex_lock(&bpfilter_lock);
__stop_umh();
mutex_unlock(&bpfilter_lock);
}
static int __bpfilter_process_sockopt(struct sock *sk, int optname,
char __user *optval,
unsigned int optlen, bool is_set)
{
struct mbox_request req;
struct mbox_reply reply;
loff_t pos;
ssize_t n;
int ret;
req.is_set = is_set;
req.pid = current->pid;
req.cmd = optname;
req.addr = (long)optval;
req.len = optlen;
mutex_lock(&bpfilter_lock);
n = __kernel_write(info.pipe_to_umh, &req, sizeof(req), &pos);
if (n != sizeof(req)) {
pr_err("write fail %zd\n", n);
__stop_umh();
ret = -EFAULT;
goto out;
}
pos = 0;
n = kernel_read(info.pipe_from_umh, &reply, sizeof(reply), &pos);
if (n != sizeof(reply)) {
pr_err("read fail %zd\n", n);
__stop_umh();
ret = -EFAULT;
goto out;
}
ret = reply.status;
out:
mutex_unlock(&bpfilter_lock);
return ret;
}
static int __init load_umh(void)
{
int err;
/* fork usermode process */
err = fork_usermode_blob(&UMH_start, &UMH_end - &UMH_start, &info);
if (err)
return err;
pr_info("Loaded bpfilter_umh pid %d\n", info.pid);
/* health check that usermode process started correctly */
if (__bpfilter_process_sockopt(NULL, 0, 0, 0, 0) != 0) {
stop_umh();
return -EFAULT;
}
bpfilter_process_sockopt = &__bpfilter_process_sockopt;
return 0;
}
static void __exit fini_umh(void)
{
stop_umh();
}
module_init(load_umh);
module_exit(fini_umh);
MODULE_LICENSE("GPL");
// SPDX-License-Identifier: GPL-2.0
#define _GNU_SOURCE
#include <sys/uio.h>
#include <errno.h>
#include <stdio.h>
#include <sys/socket.h>
#include <fcntl.h>
#include <unistd.h>
#include "include/uapi/linux/bpf.h"
#include <asm/unistd.h>
#include "msgfmt.h"
int debug_fd;
static int handle_get_cmd(struct mbox_request *cmd)
{
switch (cmd->cmd) {
case 0:
return 0;
default:
break;
}
return -ENOPROTOOPT;
}
static int handle_set_cmd(struct mbox_request *cmd)
{
return -ENOPROTOOPT;
}
static void loop(void)
{
while (1) {
struct mbox_request req;
struct mbox_reply reply;
int n;
n = read(0, &req, sizeof(req));
if (n != sizeof(req)) {
dprintf(debug_fd, "invalid request %d\n", n);
return;
}
reply.status = req.is_set ?
handle_set_cmd(&req) :
handle_get_cmd(&req);
n = write(1, &reply, sizeof(reply));
if (n != sizeof(reply)) {
dprintf(debug_fd, "reply failed %d\n", n);
return;
}
}
}
int main(void)
{
debug_fd = open("/dev/console", 00000002 | 00000100);
dprintf(debug_fd, "Started bpfilter\n");
loop();
close(debug_fd);
return 0;
}
/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _NET_BPFILTER_MSGFMT_H
#define _NET_BPFILTER_MSGFMT_H
struct mbox_request {
__u64 addr;
__u32 len;
__u32 is_set;
__u32 cmd;
__u32 pid;
};
struct mbox_reply {
__u32 status;
};
#endif
......@@ -16,6 +16,8 @@ obj-y := route.o inetpeer.o protocol.o \
inet_fragment.o ping.o ip_tunnel_core.o gre_offload.o \
metrics.o
obj-$(CONFIG_BPFILTER) += bpfilter/
obj-$(CONFIG_NET_IP_TUNNEL) += ip_tunnel.o
obj-$(CONFIG_SYSCTL) += sysctl_net_ipv4.o
obj-$(CONFIG_PROC_FS) += proc.o
......
obj-$(CONFIG_BPFILTER) += sockopt.o
// SPDX-License-Identifier: GPL-2.0
#include <linux/uaccess.h>
#include <linux/bpfilter.h>
#include <uapi/linux/bpf.h>
#include <linux/wait.h>
#include <linux/kmod.h>
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);
}
......@@ -47,6 +47,8 @@
#include <linux/errqueue.h>
#include <linux/uaccess.h>
#include <linux/bpfilter.h>
/*
* SOL_IP control messages.
*/
......@@ -1244,6 +1246,11 @@ int ip_setsockopt(struct sock *sk, int level,
return -ENOPROTOOPT;
err = do_ip_setsockopt(sk, level, optname, optval, optlen);
#ifdef CONFIG_BPFILTER
if (optname >= BPFILTER_IPT_SO_SET_REPLACE &&
optname < BPFILTER_IPT_SET_MAX)
err = bpfilter_ip_set_sockopt(sk, optname, optval, optlen);
#endif
#ifdef CONFIG_NETFILTER
/* we need to exclude all possible ENOPROTOOPTs except default case */
if (err == -ENOPROTOOPT && optname != IP_HDRINCL &&
......@@ -1552,6 +1559,11 @@ int ip_getsockopt(struct sock *sk, int level,
int err;
err = do_ip_getsockopt(sk, level, optname, optval, optlen, 0);
#ifdef CONFIG_BPFILTER
if (optname >= BPFILTER_IPT_SO_GET_INFO &&
optname < BPFILTER_IPT_GET_MAX)
err = bpfilter_ip_get_sockopt(sk, optname, optval, optlen);
#endif
#ifdef CONFIG_NETFILTER
/* we need to exclude all possible ENOPROTOOPTs except default case */
if (err == -ENOPROTOOPT && optname != IP_PKTOPTIONS &&
......@@ -1584,6 +1596,11 @@ int compat_ip_getsockopt(struct sock *sk, int level, int optname,
err = do_ip_getsockopt(sk, level, optname, optval, optlen,
MSG_CMSG_COMPAT);
#ifdef CONFIG_BPFILTER
if (optname >= BPFILTER_IPT_SO_GET_INFO &&
optname < BPFILTER_IPT_GET_MAX)
err = bpfilter_ip_get_sockopt(sk, optname, optval, optlen);
#endif
#ifdef CONFIG_NETFILTER
/* we need to exclude all possible ENOPROTOOPTs except default case */
if (err == -ENOPROTOOPT && optname != IP_PKTOPTIONS &&
......
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