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Alexei Starovoitovdavem330
Alexei Starovoitov
authored and
davem330
committedMay 23, 2018
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 <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
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‎include/linux/bpfilter.h

+15
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,15 @@
1+
/* SPDX-License-Identifier: GPL-2.0 */
2+
#ifndef _LINUX_BPFILTER_H
3+
#define _LINUX_BPFILTER_H
4+
5+
#include <uapi/linux/bpfilter.h>
6+
7+
struct sock;
8+
int bpfilter_ip_set_sockopt(struct sock *sk, int optname, char *optval,
9+
unsigned int optlen);
10+
int bpfilter_ip_get_sockopt(struct sock *sk, int optname, char *optval,
11+
int *optlen);
12+
extern int (*bpfilter_process_sockopt)(struct sock *sk, int optname,
13+
char __user *optval,
14+
unsigned int optlen, bool is_set);
15+
#endif

‎include/uapi/linux/bpfilter.h

+21
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,21 @@
1+
/* SPDX-License-Identifier: GPL-2.0 */
2+
#ifndef _UAPI_LINUX_BPFILTER_H
3+
#define _UAPI_LINUX_BPFILTER_H
4+
5+
#include <linux/if.h>
6+
7+
enum {
8+
BPFILTER_IPT_SO_SET_REPLACE = 64,
9+
BPFILTER_IPT_SO_SET_ADD_COUNTERS = 65,
10+
BPFILTER_IPT_SET_MAX,
11+
};
12+
13+
enum {
14+
BPFILTER_IPT_SO_GET_INFO = 64,
15+
BPFILTER_IPT_SO_GET_ENTRIES = 65,
16+
BPFILTER_IPT_SO_GET_REVISION_MATCH = 66,
17+
BPFILTER_IPT_SO_GET_REVISION_TARGET = 67,
18+
BPFILTER_IPT_GET_MAX,
19+
};
20+
21+
#endif /* _UAPI_LINUX_BPFILTER_H */

‎net/Kconfig

+2
Original file line numberDiff line numberDiff line change
@@ -202,6 +202,8 @@ source "net/bridge/netfilter/Kconfig"
202202

203203
endif
204204

205+
source "net/bpfilter/Kconfig"
206+
205207
source "net/dccp/Kconfig"
206208
source "net/sctp/Kconfig"
207209
source "net/rds/Kconfig"

‎net/Makefile

+1
Original file line numberDiff line numberDiff line change
@@ -20,6 +20,7 @@ obj-$(CONFIG_TLS) += tls/
2020
obj-$(CONFIG_XFRM) += xfrm/
2121
obj-$(CONFIG_UNIX) += unix/
2222
obj-$(CONFIG_NET) += ipv6/
23+
obj-$(CONFIG_BPFILTER) += bpfilter/
2324
obj-$(CONFIG_PACKET) += packet/
2425
obj-$(CONFIG_NET_KEY) += key/
2526
obj-$(CONFIG_BRIDGE) += bridge/

‎net/bpfilter/Kconfig

+16
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,16 @@
1+
menuconfig BPFILTER
2+
bool "BPF based packet filtering framework (BPFILTER)"
3+
default n
4+
depends on NET && BPF
5+
help
6+
This builds experimental bpfilter framework that is aiming to
7+
provide netfilter compatible functionality via BPF
8+
9+
if BPFILTER
10+
config BPFILTER_UMH
11+
tristate "bpfilter kernel module with user mode helper"
12+
default m
13+
help
14+
This builds bpfilter kernel module with embedded user mode helper
15+
endif
16+

‎net/bpfilter/Makefile

+30
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,30 @@
1+
# SPDX-License-Identifier: GPL-2.0
2+
#
3+
# Makefile for the Linux BPFILTER layer.
4+
#
5+
6+
hostprogs-y := bpfilter_umh
7+
bpfilter_umh-objs := main.o
8+
HOSTCFLAGS += -I. -Itools/include/
9+
ifeq ($(CONFIG_BPFILTER_UMH), y)
10+
# builtin bpfilter_umh should be compiled with -static
11+
# since rootfs isn't mounted at the time of __init
12+
# function is called and do_execv won't find elf interpreter
13+
HOSTLDFLAGS += -static
14+
endif
15+
16+
# a bit of elf magic to convert bpfilter_umh binary into a binary blob
17+
# inside bpfilter_umh.o elf file referenced by
18+
# _binary_net_bpfilter_bpfilter_umh_start symbol
19+
# which bpfilter_kern.c passes further into umh blob loader at run-time
20+
quiet_cmd_copy_umh = GEN $@
21+
cmd_copy_umh = echo ':' > $(obj)/.bpfilter_umh.o.cmd; \
22+
$(OBJCOPY) -I binary -O $(CONFIG_OUTPUT_FORMAT) \
23+
-B `$(OBJDUMP) -f $<|grep architecture|cut -d, -f1|cut -d' ' -f2` \
24+
--rename-section .data=.init.rodata $< $@
25+
26+
$(obj)/bpfilter_umh.o: $(obj)/bpfilter_umh
27+
$(call cmd,copy_umh)
28+
29+
obj-$(CONFIG_BPFILTER_UMH) += bpfilter.o
30+
bpfilter-objs += bpfilter_kern.o bpfilter_umh.o

‎net/bpfilter/bpfilter_kern.c

+111
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,111 @@
1+
// SPDX-License-Identifier: GPL-2.0
2+
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
3+
#include <linux/init.h>
4+
#include <linux/module.h>
5+
#include <linux/umh.h>
6+
#include <linux/bpfilter.h>
7+
#include <linux/sched.h>
8+
#include <linux/sched/signal.h>
9+
#include <linux/fs.h>
10+
#include <linux/file.h>
11+
#include "msgfmt.h"
12+
13+
#define UMH_start _binary_net_bpfilter_bpfilter_umh_start
14+
#define UMH_end _binary_net_bpfilter_bpfilter_umh_end
15+
16+
extern char UMH_start;
17+
extern char UMH_end;
18+
19+
static struct umh_info info;
20+
/* since ip_getsockopt() can run in parallel, serialize access to umh */
21+
static DEFINE_MUTEX(bpfilter_lock);
22+
23+
static void shutdown_umh(struct umh_info *info)
24+
{
25+
struct task_struct *tsk;
26+
27+
tsk = pid_task(find_vpid(info->pid), PIDTYPE_PID);
28+
if (tsk)
29+
force_sig(SIGKILL, tsk);
30+
fput(info->pipe_to_umh);
31+
fput(info->pipe_from_umh);
32+
}
33+
34+
static void __stop_umh(void)
35+
{
36+
if (bpfilter_process_sockopt) {
37+
bpfilter_process_sockopt = NULL;
38+
shutdown_umh(&info);
39+
}
40+
}
41+
42+
static void stop_umh(void)
43+
{
44+
mutex_lock(&bpfilter_lock);
45+
__stop_umh();
46+
mutex_unlock(&bpfilter_lock);
47+
}
48+
49+
static int __bpfilter_process_sockopt(struct sock *sk, int optname,
50+
char __user *optval,
51+
unsigned int optlen, bool is_set)
52+
{
53+
struct mbox_request req;
54+
struct mbox_reply reply;
55+
loff_t pos;
56+
ssize_t n;
57+
int ret;
58+
59+
req.is_set = is_set;
60+
req.pid = current->pid;
61+
req.cmd = optname;
62+
req.addr = (long)optval;
63+
req.len = optlen;
64+
mutex_lock(&bpfilter_lock);
65+
n = __kernel_write(info.pipe_to_umh, &req, sizeof(req), &pos);
66+
if (n != sizeof(req)) {
67+
pr_err("write fail %zd\n", n);
68+
__stop_umh();
69+
ret = -EFAULT;
70+
goto out;
71+
}
72+
pos = 0;
73+
n = kernel_read(info.pipe_from_umh, &reply, sizeof(reply), &pos);
74+
if (n != sizeof(reply)) {
75+
pr_err("read fail %zd\n", n);
76+
__stop_umh();
77+
ret = -EFAULT;
78+
goto out;
79+
}
80+
ret = reply.status;
81+
out:
82+
mutex_unlock(&bpfilter_lock);
83+
return ret;
84+
}
85+
86+
static int __init load_umh(void)
87+
{
88+
int err;
89+
90+
/* fork usermode process */
91+
err = fork_usermode_blob(&UMH_start, &UMH_end - &UMH_start, &info);
92+
if (err)
93+
return err;
94+
pr_info("Loaded bpfilter_umh pid %d\n", info.pid);
95+
96+
/* health check that usermode process started correctly */
97+
if (__bpfilter_process_sockopt(NULL, 0, 0, 0, 0) != 0) {
98+
stop_umh();
99+
return -EFAULT;
100+
}
101+
bpfilter_process_sockopt = &__bpfilter_process_sockopt;
102+
return 0;
103+
}
104+
105+
static void __exit fini_umh(void)
106+
{
107+
stop_umh();
108+
}
109+
module_init(load_umh);
110+
module_exit(fini_umh);
111+
MODULE_LICENSE("GPL");

‎net/bpfilter/main.c

+63
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@@ -0,0 +1,63 @@
1+
// SPDX-License-Identifier: GPL-2.0
2+
#define _GNU_SOURCE
3+
#include <sys/uio.h>
4+
#include <errno.h>
5+
#include <stdio.h>
6+
#include <sys/socket.h>
7+
#include <fcntl.h>
8+
#include <unistd.h>
9+
#include "include/uapi/linux/bpf.h"
10+
#include <asm/unistd.h>
11+
#include "msgfmt.h"
12+
13+
int debug_fd;
14+
15+
static int handle_get_cmd(struct mbox_request *cmd)
16+
{
17+
switch (cmd->cmd) {
18+
case 0:
19+
return 0;
20+
default:
21+
break;
22+
}
23+
return -ENOPROTOOPT;
24+
}
25+
26+
static int handle_set_cmd(struct mbox_request *cmd)
27+
{
28+
return -ENOPROTOOPT;
29+
}
30+
31+
static void loop(void)
32+
{
33+
while (1) {
34+
struct mbox_request req;
35+
struct mbox_reply reply;
36+
int n;
37+
38+
n = read(0, &req, sizeof(req));
39+
if (n != sizeof(req)) {
40+
dprintf(debug_fd, "invalid request %d\n", n);
41+
return;
42+
}
43+
44+
reply.status = req.is_set ?
45+
handle_set_cmd(&req) :
46+
handle_get_cmd(&req);
47+
48+
n = write(1, &reply, sizeof(reply));
49+
if (n != sizeof(reply)) {
50+
dprintf(debug_fd, "reply failed %d\n", n);
51+
return;
52+
}
53+
}
54+
}
55+
56+
int main(void)
57+
{
58+
debug_fd = open("/dev/console", 00000002 | 00000100);
59+
dprintf(debug_fd, "Started bpfilter\n");
60+
loop();
61+
close(debug_fd);
62+
return 0;
63+
}

‎net/bpfilter/msgfmt.h

+17
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,17 @@
1+
/* SPDX-License-Identifier: GPL-2.0 */
2+
#ifndef _NET_BPFILTER_MSGFMT_H
3+
#define _NET_BPFILTER_MSGFMT_H
4+
5+
struct mbox_request {
6+
__u64 addr;
7+
__u32 len;
8+
__u32 is_set;
9+
__u32 cmd;
10+
__u32 pid;
11+
};
12+
13+
struct mbox_reply {
14+
__u32 status;
15+
};
16+
17+
#endif

‎net/ipv4/Makefile

+2
Original file line numberDiff line numberDiff line change
@@ -16,6 +16,8 @@ obj-y := route.o inetpeer.o protocol.o \
1616
inet_fragment.o ping.o ip_tunnel_core.o gre_offload.o \
1717
metrics.o
1818

19+
obj-$(CONFIG_BPFILTER) += bpfilter/
20+
1921
obj-$(CONFIG_NET_IP_TUNNEL) += ip_tunnel.o
2022
obj-$(CONFIG_SYSCTL) += sysctl_net_ipv4.o
2123
obj-$(CONFIG_PROC_FS) += proc.o

‎net/ipv4/bpfilter/Makefile

+2
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,2 @@
1+
obj-$(CONFIG_BPFILTER) += sockopt.o
2+

‎net/ipv4/bpfilter/sockopt.c

+42
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,42 @@
1+
// SPDX-License-Identifier: GPL-2.0
2+
#include <linux/uaccess.h>
3+
#include <linux/bpfilter.h>
4+
#include <uapi/linux/bpf.h>
5+
#include <linux/wait.h>
6+
#include <linux/kmod.h>
7+
8+
int (*bpfilter_process_sockopt)(struct sock *sk, int optname,
9+
char __user *optval,
10+
unsigned int optlen, bool is_set);
11+
EXPORT_SYMBOL_GPL(bpfilter_process_sockopt);
12+
13+
int bpfilter_mbox_request(struct sock *sk, int optname, char __user *optval,
14+
unsigned int optlen, bool is_set)
15+
{
16+
if (!bpfilter_process_sockopt) {
17+
int err = request_module("bpfilter");
18+
19+
if (err)
20+
return err;
21+
if (!bpfilter_process_sockopt)
22+
return -ECHILD;
23+
}
24+
return bpfilter_process_sockopt(sk, optname, optval, optlen, is_set);
25+
}
26+
27+
int bpfilter_ip_set_sockopt(struct sock *sk, int optname, char __user *optval,
28+
unsigned int optlen)
29+
{
30+
return bpfilter_mbox_request(sk, optname, optval, optlen, true);
31+
}
32+
33+
int bpfilter_ip_get_sockopt(struct sock *sk, int optname, char __user *optval,
34+
int __user *optlen)
35+
{
36+
int len;
37+
38+
if (get_user(len, optlen))
39+
return -EFAULT;
40+
41+
return bpfilter_mbox_request(sk, optname, optval, len, false);
42+
}

‎net/ipv4/ip_sockglue.c

+17
Original file line numberDiff line numberDiff line change
@@ -47,6 +47,8 @@
4747
#include <linux/errqueue.h>
4848
#include <linux/uaccess.h>
4949

50+
#include <linux/bpfilter.h>
51+
5052
/*
5153
* SOL_IP control messages.
5254
*/
@@ -1244,6 +1246,11 @@ int ip_setsockopt(struct sock *sk, int level,
12441246
return -ENOPROTOOPT;
12451247

12461248
err = do_ip_setsockopt(sk, level, optname, optval, optlen);
1249+
#ifdef CONFIG_BPFILTER
1250+
if (optname >= BPFILTER_IPT_SO_SET_REPLACE &&
1251+
optname < BPFILTER_IPT_SET_MAX)
1252+
err = bpfilter_ip_set_sockopt(sk, optname, optval, optlen);
1253+
#endif
12471254
#ifdef CONFIG_NETFILTER
12481255
/* we need to exclude all possible ENOPROTOOPTs except default case */
12491256
if (err == -ENOPROTOOPT && optname != IP_HDRINCL &&
@@ -1552,6 +1559,11 @@ int ip_getsockopt(struct sock *sk, int level,
15521559
int err;
15531560

15541561
err = do_ip_getsockopt(sk, level, optname, optval, optlen, 0);
1562+
#ifdef CONFIG_BPFILTER
1563+
if (optname >= BPFILTER_IPT_SO_GET_INFO &&
1564+
optname < BPFILTER_IPT_GET_MAX)
1565+
err = bpfilter_ip_get_sockopt(sk, optname, optval, optlen);
1566+
#endif
15551567
#ifdef CONFIG_NETFILTER
15561568
/* we need to exclude all possible ENOPROTOOPTs except default case */
15571569
if (err == -ENOPROTOOPT && optname != IP_PKTOPTIONS &&
@@ -1584,6 +1596,11 @@ int compat_ip_getsockopt(struct sock *sk, int level, int optname,
15841596
err = do_ip_getsockopt(sk, level, optname, optval, optlen,
15851597
MSG_CMSG_COMPAT);
15861598

1599+
#ifdef CONFIG_BPFILTER
1600+
if (optname >= BPFILTER_IPT_SO_GET_INFO &&
1601+
optname < BPFILTER_IPT_GET_MAX)
1602+
err = bpfilter_ip_get_sockopt(sk, optname, optval, optlen);
1603+
#endif
15871604
#ifdef CONFIG_NETFILTER
15881605
/* we need to exclude all possible ENOPROTOOPTs except default case */
15891606
if (err == -ENOPROTOOPT && optname != IP_PKTOPTIONS &&

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