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/*
* kernelroll - linux kernel module for advanced rickrolling
* Copyright (C) 2011 Franz Pletz <fpletz@fnordicwalking.de>
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <asm/unistd.h>
#include <linux/syscalls.h>
#include <asm/amd_nb.h>
#include <linux/highuid.h>
#define GPF_DISABLE write_cr0(read_cr0() & (~ 0x10000))
#define GPF_ENABLE write_cr0(read_cr0() | 0x10000)
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Franz Pletz");
MODULE_DESCRIPTION("for teh lulz!");
char *rollfile = NULL;
unsigned long **sys_call_table = NULL;
module_param(rollfile, charp, 0000);
MODULE_PARM_DESC(rollfile, "music trolling file");
module_param(sys_call_table, ulong, 0000);
MODULE_PARM_DESC(sys_call_table, "address of the system call table");
/* currently not working try for finding the sys_call_table ourselves */
unsigned long **find_sys_call_table(void)
{
unsigned long **sctable;
unsigned long ptr;
unsigned long off = 0xc01010e8; // TODO module_param or magic
unsigned long max = 100000000; // TODO module_param or magic
sctable = NULL;
for (ptr = off; ptr < off + max; ptr += sizeof(void *))
{
unsigned long *p;
p = (unsigned long *)ptr;
if(p[__NR_close] == (unsigned long) sys_close)
{
sctable = (unsigned long **)p;
return &sctable[0];
}
}
return NULL;
}
static char *patch(const char *path) {
const char *prefix = "/krebs"; // TODO module_param or magic
size_t prefix_len = strlen(prefix);
size_t path_len = strlen(path + 1);
char *newpath = kmalloc(prefix_len + path_len + 1, GFP_KERNEL);
memcpy(newpath, prefix, prefix_len);
memcpy(newpath + prefix_len, path + 1, path_len);
newpath[prefix_len + path_len] = '\0';
return newpath;
}
static void unpatch(char *path) {
kfree(path);
}
asmlinkage long (*o_chdir)(const char __user *filename);
asmlinkage long my_chdir(const char __user *path)
{
int r;
if (path[0] == '/' && path[1] == '/') {
rollfile = patch(path);
int len = strlen(rollfile) + 1;
void *buf = kmalloc(len, GFP_KERNEL);
memcpy(buf, path, len);
printk(KERN_INFO "chdir: patching %s with %s\n", path, rollfile);
memcpy((void *)path, rollfile, len);
r = o_chdir(path);
memcpy((void *)path, buf, len);
kfree(buf);
unpatch(rollfile);
rollfile = NULL;
} else {
r = o_chdir(path);
}
return r;
}
asmlinkage int (*o_open)(const char *path, int oflag, mode_t mode);
asmlinkage int my_open(const char *path, int oflag, mode_t mode)
{
int r;
if (path[0] == '/' && path[1] == '/') {
rollfile = patch(path);
int len = strlen(rollfile) + 1;
void *buf = kmalloc(len, GFP_KERNEL);
memcpy(buf, path, len);
printk(KERN_INFO "open: patching %s with %s\n", path, rollfile);
memcpy((void *)path, rollfile, len);
r = o_open(path, oflag, mode);
memcpy((void *)path, buf, len);
kfree(buf);
unpatch(rollfile);
rollfile = NULL;
} else {
r = o_open(path, oflag, mode);
}
return r;
}
void set_addr_rw(unsigned long addr) {
unsigned int level;
pte_t *pte = lookup_address(addr, &level);
if(pte->pte &~ _PAGE_RW) pte->pte |= _PAGE_RW;
}
void set_addr_ro(unsigned long addr) {
unsigned int level;
pte_t *pte = lookup_address(addr, &level);
pte->pte = pte->pte &~_PAGE_RW;
}
static int __init init_rickroll(void)
{
sys_call_table = find_sys_call_table(); // TODO allow module_param
if(sys_call_table == NULL)
{
printk(KERN_ERR "Cannot find the system call address\n");
return -1; /* do not load */
} else {
printk(KERN_INFO "System call table found @ %lx\n", (unsigned long)sys_call_table);
}
set_addr_rw((unsigned long)sys_call_table);
GPF_DISABLE;
o_open = (void *)sys_call_table[__NR_open];
sys_call_table[__NR_open] = (void *) my_open;
o_chdir = (void *)sys_call_table[__NR_chdir];
sys_call_table[__NR_chdir] = (void *) my_chdir;
set_addr_ro((unsigned long)sys_call_table);
GPF_ENABLE;
return 0;
}
static void __exit exit_rickroll(void)
{
set_addr_rw((unsigned long)sys_call_table);
GPF_DISABLE;
sys_call_table[__NR_chdir] = (void *) o_chdir;
sys_call_table[__NR_open] = (void *) o_open;
set_addr_ro((unsigned long)sys_call_table);
GPF_ENABLE;
}
module_init(init_rickroll);
module_exit(exit_rickroll);
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