Execute shell command from other user

This is a discussion on Execute shell command from other user within the C++ Programming forums, part of the General Programming Boards category; I want to execute shell command by user with uid 501. I run this application by root. I wrote: Code: ...

  1. #1
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    Execute shell command from other user

    I want to execute shell command by user with uid 501. I run this application by root. I wrote:
    Code:
    #include <iostream>
    using namespace std;
    #include <stdlib.h>
    #include <sys/types.h>
    #include <unistd.h>
    #include <stdio.h>
    
    
    int main() {
    	
    //cout<<"started as uid="<<getuid()<<", pid="<<getpid()<<endl;
    	
            pid_t result = fork();
    
    	if (result==-1) {cout<<"error fork()"<<endl;
    	return 1;} else cout<<"fork()="<<result<<endl;
    
    	if(result==0){
    	int status=setuid(501);
    	
    //cout<<"child print setuid()="<<status<<endl;
    
    	if(status>0)
    	{
    
    //cout<<"child uid="<<getuid()<<endl;
    //cout<<"child pid="<<getpid()<<endl;
    
    sleep(20);
    
    
    system("date >/media/disk/log");
    system("whoami >/media/disk/log");
    
    
    	}} else if(result!=0){
    		
    //cout<<"parent uid="<<getuid()<<endl;
    //cout<<"parent pid="<<getpid()<<endl;}
    
    	return 0;
    }
    but /media/disk/log is empty.

  2. #2
    spurious conceit MK27's Avatar
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    move to C++
    C programming resources:
    GNU C Function and Macro Index -- glibc reference manual
    The C Book -- nice online learner guide
    Current ISO draft standard
    CCAN -- new CPAN like open source library repository
    3 (different) GNU debugger tutorials: #1 -- #2 -- #3
    cpwiki -- our wiki on sourceforge

  3. #3
    and the Hat of Guessing tabstop's Avatar
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    While we wait for the move to C++, I will ask: do you get any error messages on the console? Does the user have privileges to write to /media/disk/log? Are you aware that using > as redirect will delete any previous contents of the file, meaning you'll never see the date?

  4. #4
    and the hat of wrongness Salem's Avatar
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    Such a short program, yet somehow unreadable.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

  5. #5
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    Quote Originally Posted by Salem View Post
    Such a short program, yet somehow unreadable.

    I guess that's an achievement in itself.
    "What's up, Doc?"
    "'Up' is a relative concept. It has no intrinsic value."

  6. #6
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    Excuse for unreadable.

    While we wait for the move to C++, I will ask: do you get any error messages on the console? Does the user have privileges to write to /media/disk/log? Are you aware that using > as redirect will delete any previous contents of the file, meaning you'll never see the date?
    Code:
    [andrew@COR disk]$ ls -l
    -rwxrwxrwx.   1 root   root          6 Авг 23 18:37 log
    I know that > will delete any previous contents of the file.
    Before:
    Code:
    [andrew@COR disk]$ cat log
    empty file
    After:
    Code:
    [root@COR Release]# ./ssetu
    started as uid=0, pid=8859
    fork()=0
    child print setuid()=0
    fork()=8860
    parent uid=0
    parent pid=8859
    [root@COR Release]# cat /media/disk/log
    empty file
    My attempt to make a code more readable:

    Code:
    #include <iostream>
    using namespace std;
    #include <stdlib.h>
    #include <sys/types.h>
    #include <unistd.h>
    #include <stdio.h>
    
    
    int main() {
    	
            pid_t result = fork();
    
    	if (result==-1)   {
                 cout<<"error fork()"<<endl;
    	     return 1;
            
             } else 
                 cout<<"fork()="<<result<<endl;
    
    	if (result==0){
    	       int status=setuid(501);
    	
      	       if (status>0){
                              sleep(20);
                              system("date >/media/disk/log");
                    }
    
             } 
    	return 0;
    }

  7. #7
    and the Hat of Guessing tabstop's Avatar
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    If you take away the redirect, do you get any output?

  8. #8
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    Quote Originally Posted by tabstop View Post
    If you take away the redirect, do you get any output?
    no, if i run by root or by user with uid=501 i get nothing.
    by root:
    Code:
    [root@COR Release]# ./ssetu
    started as uid=0, pid=9571
    fork()=9572
    parent uid=0
    parent pid=9571
    fork()=0
    child print setuid()=0
    by uid=501:
    Code:
    [andrew@COR disk]$ ./ssetu
    started as uid=501, pid=9601
    fork()=9602
    parent uid=501
    parent pid=9601
    fork()=0
    child print setuid()=0
    by other user:
    Code:
    [up@COR disk]$ ./ssetu
    started as uid=500, pid=9537
    fork()=9538
    parent uid=500
    parent pid=9537
    fork()=0
    child print setuid()=-1
    Last edited by LuckyStr; 08-23-2009 at 05:11 PM.

  9. #9
    and the Hat of Guessing tabstop's Avatar
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    So ... that would be why your file is empty. Can you type "date" or "whoami" at the terminal? Does uid 501 not have a name that whoami doesn't print?

  10. #10
    Captain Crash brewbuck's Avatar
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    Here's my implementation:

    Code:
    sudo -u \#501 command
    Code:
    //try
    //{
    	if (a) do { f( b); } while(1);
    	else   do { f(!b); } while(1);
    //}

  11. #11
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    Quote Originally Posted by tabstop View Post
    So ... that would be why your file is empty. Can you type "date" or "whoami" at the terminal? Does uid 501 not have a name that whoami doesn't print?
    Code:
    [andrew@COR up]$ id
    uid=501(andrew) gid=501(andrew) группы=500(up),501(andrew),502(vboxusers) context=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023
    [andrew@COR up]$ whoami
    andrew
    [andrew@COR up]$ date
    Пнд Авг 24 16:44:30 EEST 2009
    [andrew@COR up]$

  12. #12
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    What if you execute
    date >/media/disk/log
    as user andrew?

    Or try to use the full path to date, as the $PATH environment variable might be not set.

  13. #13
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    Thank's all, but my mistake was that i check wrong value: if setuid() finished successfully it return 0.

    Code:
    #include <iostream>
    using namespace std;
    #include <stdlib.h>
    #include <sys/types.h>
    #include <unistd.h>
    #include <stdio.h>
    
    
    int main() {
    	
            pid_t result = fork();
    
    	if (result==-1)   {
                 cout<<"error fork()"<<endl;
    	     return 1;
            
             } else 
                 cout<<"fork()="<<result<<endl;
    
    	if (result==0){
    	       int status=setuid(501);
    	
      	       if (status==0){
                              sleep(20);
                              system("date >/media/disk/log");
                    }
    
             } 
    	return 0;
    }

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