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测试了albcamus版主给的劫持execve,open调用的例程。由于我的2.6.18的内核上的有个结构体和2.6.22(albcamus版主的例程)上的不一致,暂时屏蔽了劫持execve的代码,这里仅劫持open系统调用,修改后的代码如下:
- #include <linux/kernel.h>
- #include <linux/init.h>
- #include <linux/module.h>
- #include <linux/kprobes.h>
- #include <linux/kallsyms.h>
- #include <linux/sched.h>
- #include <linux/ptrace.h>
- #include <linux/mm.h>
- #include <linux/smp.h>
- #include <linux/user.h>
- #include <linux/errno.h>
- #include <linux/cpu.h>
- #include <asm/uaccess.h>
- #include <asm/fcntl.h>
- #include <asm/unistd.h>
- MODULE_DESCRIPTION("Intercept the system call table in Linux");
- MODULE_AUTHOR("alert7 ([email]alert7@xfocus.org[/email]) \n\t\talbcamus <[email]albcamus@gmail.com[/email]>");
- MODULE_LICENSE("GPL");
- /* comment the following line to shut me up */
- #define INTERCEPT_DEBUG
- #ifdef INTERCEPT_DEBUG
- #define dbgprint(format,args...) \
- printk("intercept: function:%s-L%d: "format, __FUNCTION__, __LINE__, ##args);
- #else
- #define dbgprint(format,args...) do {} while(0);
- #endif
- /**
- * the system call table
- */
- void **my_table;
- unsigned int orig_cr0;
- /**
- * the original syscall functions
- */
- asmlinkage long (*old_open) (char __user *filename, int flags, int mode);
- asmlinkage int (*old_execve) (struct pt_regs regs);
- /** do_execve and do_fork */
- unsigned int can_exec_fork = 0;
- int (*new_do_execve) (char * filename,
- char __user *__user *argv,
- char __user *__user *envp,
- struct pt_regs * regs);
- struct idtr {
- unsigned short limit;
- unsigned int base;
- } __attribute__ ((packed));
- struct idt {
- unsigned short off1;
- unsigned short sel;
- unsigned char none, flags;
- unsigned short off2;
- } __attribute__ ((packed));
- #if 0
- /**
- * check if we can intercept fork/vfork/clone/execve or not
- *
- * return : 0 for no, 1 for yes
- */
- struct kprobe kp_exec;
- unsigned int can_intercept_fork_exec(void)
- {
- int ret = 0;
- #ifndef CONFIG_KPROBES
- return ret;
- #endif
- kp_exec.symbol_name = "do_execve";
- ret = register_kprobe(&kp_exec);
- if (ret != 0 ) {
- dbgprint("cannot find do_execve by kprobe.\n");
- return 0;
- }
- new_do_execve = ( int (*)
- (char *,
- char __user * __user *,
- char __user * __user *,
- struct pt_regs *
- )
- ) kp_exec.addr;
- dbgprint("do_execve at %p\n", (void *)kp_exec.addr);
- unregister_kprobe(&kp_exec);
- return 1;
- }
- #endif
- /**
- * clear WP bit of CR0, and return the original value
- */
- unsigned int clear_and_return_cr0(void)
- {
- unsigned int cr0 = 0;
- unsigned int ret;
- asm volatile ("movl %%cr0, %%eax"
- : "=a"(cr0)
- );
- ret = cr0;
- /* clear the 20 bit of CR0, a.k.a WP bit */
- cr0 &= 0xfffeffff;
- asm volatile ("movl %%eax, %%cr0"
- :
- : "a"(cr0)
- );
- return ret;
- }
- /** set CR0 with new value
- *
- * @val : new value to set in cr0
- */
- void setback_cr0(unsigned int val)
- {
- asm volatile ("movl %%eax, %%cr0"
- :
- : "a"(val)
- );
- }
- /**
- * Return the first appearence of NEEDLE in HAYSTACK.
- * */
- static void *memmem(const void *haystack, size_t haystack_len,
- const void *needle, size_t needle_len)
- {/*{{{*/
- const char *begin;
- const char *const last_possible
- = (const char *) haystack + haystack_len - needle_len;
- if (needle_len == 0)
- /* The first occurrence of the empty string is deemed to occur at
- the beginning of the string. */
- return (void *) haystack;
- /* Sanity check, otherwise the loop might search through the whole
- memory. */
- if (__builtin_expect(haystack_len < needle_len, 0))
- return NULL;
- for (begin = (const char *) haystack; begin <= last_possible;
- ++begin)
- if (begin[0] == ((const char *) needle)[0]
- && !memcmp((const void *) &begin[1],
- (const void *) ((const char *) needle + 1),
- needle_len - 1))
- return (void *) begin;
- return NULL;
- }/*}}}*/
- /**
- * Find the location of sys_call_table
- */
- static unsigned long get_sys_call_table(void)
- {/*{{{*/
- /* we'll read first 100 bytes of int $0x80 */
- #define OFFSET_SYSCALL 100
- struct idtr idtr;
- struct idt idt;
- unsigned sys_call_off;
- unsigned retval;
- char sc_asm[OFFSET_SYSCALL], *p;
- /* well, let's read IDTR */
- asm("sidt %0":"=m"(idtr)
- :
- :"memory" );
- dbgprint("idtr base at 0x%X\n", (unsigned int)idtr.base);
- /* Read in IDT for vector 0x80 (syscall) */
- memcpy(&idt, (char *) idtr.base + 8 * 0x80, sizeof(idt));
- sys_call_off = (idt.off2 << 16) | idt.off1;
- dbgprint("idt80: flags=%X sel=%X off=%X\n",
- (unsigned) idt.flags, (unsigned) idt.sel, sys_call_off);
- /* we have syscall routine address now, look for syscall table
- dispatch (indirect call) */
- memcpy(sc_asm, (void *)sys_call_off, OFFSET_SYSCALL);
- /**
- * Search opcode of `call sys_call_table(,eax,4)'
- */
- p = (char *) memmem(sc_asm, OFFSET_SYSCALL, "\xff\x14\x85", 3);
- if (p == NULL)
- return 0;
- retval = *(unsigned *) (p + 3);
- if (p) {
- dbgprint("sys_call_table at 0x%x, call dispatch at 0x%x\n",
- retval, (unsigned int) p);
- }
- return retval;
- #undef OFFSET_SYSCALL
- }/*}}}*/
- /**
- * new_open - replace the original sys_open when initilazing,
- * as well as be got rid of when removed
- */
- asmlinkage long new_open(char *filename, int flags, int mode)
- {
- dbgprint("hello\n");
- return old_open (filename, flags, mode);
- }
- /**
- * new_execve - you should change this function whenever the kernel's sys_execve()
- * changes
- */
- asmlinkage int new_execve(struct pt_regs regs)
- {
- int error;
- char *filename;
- dbgprint("Hello\n");
- filename = getname( (char __user *) regs.ebx );
- error = PTR_ERR(filename);
- if ( IS_ERR(filename) )
- goto out;
- dbgprint("file to execve: %s\n", filename);
- error = new_do_execve(filename,
- (char __user * __user *) regs.ecx,
- (char __user * __user *) regs.edx,
- ®s);
- if (error == 0) {
- task_lock(current);
- current->ptrace &= ~PT_DTRACE;
- task_unlock(current);
- set_thread_flag(TIF_IRET);
- }
- putname (filename);
- out:
- return error;
- }
- static int intercept_init(void)
- {
- my_table = (void **)get_sys_call_table();
- if (my_table == NULL)
- return -1;
- dbgprint("sys call table address %p\n", (void *) my_table);
- #define REPLACE(x) old_##x = my_table[__NR_##x];\
- my_table[__NR_##x] = new_##x
-
- REPLACE(open);
- #if 0
- can_exec_fork = can_intercept_fork_exec();
- if(can_exec_fork == 1)
- REPLACE(execve);
- #endif
- #undef REPLACE
- return 0;
- }
- static int __init this_init(void)
- {
- int ret;
- printk("syscall intercept: Hi, poor linux!\n");
- orig_cr0 = clear_and_return_cr0();
- ret = intercept_init();
- setback_cr0(orig_cr0);
- return ret;
- }
- static void __exit this_fini(void)
- {
- printk("syscall intercept: bye, poor linux!\n");
- #define RESTORE(x) my_table[__NR_##x] = old_##x
- orig_cr0 = clear_and_return_cr0();
- RESTORE(open);
- #if 0
- if(can_exec_fork == 1)
- RESTORE(execve);
- #endif
- setback_cr0(orig_cr0);
- #undef RESTORE
- }
- module_init(this_init);
- module_exit(this_fini);
复制代码
然后查看一下日志,看到如下信息:
Sep 24 19:06:49 localhost kernel: intercept: function:get_sys_call_table-L220: sys_call_table at 0xc11f14e0, call dispatch at 0xcebeceaa
Sep 24 19:06:49 localhost kernel: intercept: function:intercept_init-L276: sys call table address c11f14e0
Sep 24 19:06:50 localhost kernel: intercept: function:new_open-L234: hello
Sep 24 19:07:00 localhost last message repeated 460 times
可见open系统调用被成功劫持,而且系统在执行的过程中,open的调用是很频繁的。 |
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