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netlink: move docs to README

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Ciro Santilli
2018-07-06 08:56:22 +01:00
parent 3d4e0c095d
commit e05eb91add
7 changed files with 72 additions and 29 deletions
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2
kernel_module/README.adoc
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@@ -9,8 +9,6 @@ Our kernel modules!
.. link:timer.c[]
.. link:work_from_work.c[]
.. link:workqueue_cheat.c[]
. Misc
.. link:netlink.c[]
. Hardening
.. link:strlen_overflow.c[]
. Tracing

34
kernel_module/netlink.c
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@@ -1,46 +1,34 @@
/*
https://en.wikipedia.org/wiki/Netlink
https://stackoverflow.com/questions/3299386/how-to-use-netlink-socket-to-communicate-with-a-kernel-module
*/
/* https://github.com/cirosantilli/linux-kernel-module-cheat#netlink-sockets */
#include <linux/delay.h> /* usleep_range */
#include <linux/jiffies.h>
#include <linux/module.h>
#include <linux/netlink.h>
#include <linux/skbuff.h>
#include <net/sock.h>
/* Socket identifier, matches userland. TODO can be anything?
* Is there a more scalable way to do it? E.g. ioctl device,
* kernel generates one on the fly, then give it back and connect?
* https://stackoverflow.com/questions/32898173/can-i-have-more-than-32-netlink-sockets-in-kernelspace */
#define NETLINK_USER 31
#include "netlink.h"
struct sock *nl_sk = NULL;
static u32 count;
static u32 sleep;
module_param(sleep, int, S_IRUSR | S_IWUSR);
static void callback(struct sk_buff *skb)
{
char readbuf[1024];
char readbuf[9];
size_t readbuflen;
int pid;
int res;
struct nlmsghdr *nlh;
struct sk_buff *skb_out;
/* Read user message. */
nlh = (struct nlmsghdr *)skb->data;
pr_info("kernel received: %s\n", (char *)nlmsg_data(nlh));
/* Add an artificial sleep to see what happens when
* multiple requests come in at the same time.
*
* Try this out (it works):
* for i in `seq 16`; do /netlink.out & done */
usleep_range(1000000, 1000001);
/* Reply with jiffies. */
readbuflen = snprintf(readbuf, sizeof(readbuf), "%llu", (unsigned long long)jiffies);
if (sleep)
usleep_range(1000000, 1000001);
readbuflen = snprintf(readbuf, sizeof(readbuf), "%x", count);
count++;
pid = nlh->nlmsg_pid;
skb_out = nlmsg_new(readbuflen, 0);
if (!skb_out) {

10
kernel_module/netlink.h Normal file
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@@ -0,0 +1,10 @@
#ifndef NETLINK_H
#define NETLINK_H
/* Socket identifier, matches userland. TODO can be anything?
* Is there a more scalable way to do it? E.g. ioctl device,
* kernel generates one on the fly, then give it back and connect?
* https://stackoverflow.com/questions/32898173/can-i-have-more-than-32-netlink-sockets-in-kernelspace */
#define NETLINK_USER 31
#endif

11
kernel_module/user/netlink.c
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@@ -1,3 +1,5 @@
/* https://github.com/cirosantilli/linux-kernel-module-cheat#netlink-sockets */
#include <linux/netlink.h>
#include <stdio.h>
#include <stdlib.h>
@@ -5,8 +7,9 @@
#include <sys/socket.h>
#include <unistd.h>
#include "../netlink.h"
#define MAX_PAYLOAD 1024
#define NETLINK_USER 31
/* Some of these structs fields must be zeroed.
* We could brute force memset them, but
@@ -40,10 +43,10 @@ int main()
msg.msg_namelen = sizeof(dest_addr);
msg.msg_iov = &iov;
msg.msg_iovlen = 1;
printf("before sendmsg\n");
fprintf(stderr, "before sendmsg\n");
sendmsg(sock_fd, &msg, 0);
printf("after sendmsg\n");
fprintf(stderr, "after sendmsg\n");
recvmsg(sock_fd, &msg, 0);
printf("userland received: %s\n", (char *)NLMSG_DATA(nlh));
printf("%s\n", (char *)NLMSG_DATA(nlh));
close(sock_fd);
}