我目前已登录seed,在我的 Ubuntu 系统上运行 test.c 后,我获得了root许可。我只是想知道为什么system("/bin/sh")可以做出这样的改变?

首先,我在和su root中编译test.c。当我退出#时,运行文件并获取#chmod 4755 testroot

[04/03/2018 05:27] seed@ubuntu:~/Desktop/assignment$ id
uid=1000(seed) gid=1000(seed) groups=1000(seed),4(adm),24(cdrom),27(sudo),30(dip),46(plugdev),109(lpadmin),124(s 
ambashare),130(wireshark),1001(vboxsf)
[04/03/2018 05:27] seed@ubuntu:~/Desktop/assignment$ cat test.c
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>

int main(){


system("/bin/sh");
printf("successful!");
return 0;


}
[04/03/2018 05:27] seed@ubuntu:~/Desktop/assignment$ ./test
# whoami
root
# id 
uid=1000(seed) gid=1000(seed) euid=0(root) groups=0(root),4(adm),24(cdrom),27(sudo),30(dip),46(plugdev),109(lpadmin),124(sambashare),130(wireshark),1000(seed),1001(vboxsf)

- - 更新 - - -

[04/03/2018 06:03] seed@ubuntu:~/Desktop/assignment$ ls -l /bin/sh
lrwxrwxrwx 1 root root 4 Aug 13  2013 /bin/sh -> dash
[04/03/2018 06:04] seed@ubuntu:~/Desktop/assignment$ ls -l test
-rwsr-xr-x 1 root root 7198 Apr  3 05:56 test


[04/03/2018 06:14] seed@ubuntu:~/Desktop/assignment$ uname -a
Linux ubuntu 3.5.0-37-generic #58~precise1-Ubuntu SMP Wed Jul 10 17:51:56 UTC 
2013 i686 i686 i386 GNU/Linux
[04/03/2018 06:14] seed@ubuntu:~/Desktop/assignment$ ./test
# uname -a
Linux ubuntu 3.5.0-37-generic #58~precise1-Ubuntu SMP Wed Jul 10 17:51:56 UTC 2013 i686 i686 i386 GNU/Linux

答案1

首先,您以 root 身份编译程序,因此生成的二进制文件归 root 所有:

[04/03/2018 06:04] seed@ubuntu:~/Desktop/assignment$ ls -l test
-rwsr-xr-x 1 root root 7198 Apr  3 05:56 test
#            ^^^^

其次,通过运行chmod 4755 test你设置设定值点上./test

[04/03/2018 06:04] seed@ubuntu:~/Desktop/assignment$ ls -l test
-rwsr-xr-x 1 root root 7198 Apr  3 05:56 test
#  ^

这意味着,您的二进制文件以其文件所有者(=root)身份运行,而不是以启动它的用户身份运行。这就是为什么/bin/sh由它生成的也是由 root 运行的。

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