Obtaining ROOT privileges in program run by user

you may use sudo. please see

http://www.gratisoft.us/sudo/man/sudoers.html#examples

I stated that command line solutions are not an option.

please read the second line of the first comment.....

You can start an other program (with root preperties, that can only read the boot sector of a disk and write it into a pipeline you read in your own program.....)

the way it works is: (sortof, you have to readup on details for pipe(), fork(), execv*()...)

int channels[2];
pipe(channels)
if (fork()==0) {
  close (channel[1]);
  close(1);
  dup(channel[0]);
  close(channel[0]);
  execv("/opt/myapp/mbrreader","mbrreader","/dev/hda");
  exit(200);
} else {
   close(channels[0]);
   read(channels[1], mbrbuffer,sizeof(mbrbuffer))
   close (channels[1]);
}




your mbrreader.c, after compilation: chown root mbrreader, chmod o+sx mbrreader.
main()
{
    fd= open(argv[1],"r");
    read(fd,mbr,512);
    write(1,mbr,512);
    exit(0);
}


Check for errors etc..

noci,

Seems like it's exactly what I was looking for, shall slap it it compile and see how it goes...

Cheers.

it needs some work though, you can only use the above as a guide.../pseudo code.

I've been fiddling with the below code, and still cant get it going!

Can you see anything wrong with it?

Cheers,

KB.

Makefile to suite, if you care to compile...

--------CUT-----------
all: printmbr

printmbr: printmbr.o
      gcc printmbr.o -o printmbr

printmbr.o: printmbr.c
      gcc -c printmbr.c

clean:
      rm -rf *o printmbr
--------CUT-----------

#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <unistd.h>
#include <errno.h>
#include <stdlib.h> 
#define PIPE_PARENT 0
#define PIPE_CHILD 1 
int main (int argc, char *argv[])
{ 
  int channels[2]; 
  char mbr[512]; 
  pipe(channels); 
  pid_t pid = fork(); 
  if (pid == 0) { 
    // Child process, close parent's end.
    close (channels[PIPE_PARENT]); 
    // Close STDOUT
    close(1); 
    // Duplicate the child channel to STDOUT
    dup2(channels[PIPE_CHILD], 1); 
    // Close our old channel fd
    close(channels[PIPE_CHILD]); 
    // Execute a file, hopefully anything it prints to STDOUT shoots straight through
    // our channel[PIPE_CHILD]
    execv("echo","Test message!"); 
    exit(100); 
  } else if (pid > 0) { 
    // Parent, close childs end.
    close(channels[PIPE_CHILD]); 
    // Open the parent's end
    FILE *f = fdopen(channels[PIPE_PARENT], "r"); 
    if (f == NULL) {
      printf("ERROR: Failed to open channel PIPE_PARENT, errno = %d\n", errno);
    } else {
      // Should read the char 'T'...
      printf("fread(PIPE_PARENT): %d, errno = %d\n", fread(&mbr, 1, 1, f), errno);
      fclose(f);
    } 
    close(channels[PIPE_PARENT]); 
  } else { 
    // Failure
    printf("ERROR: FORK Failed, errno = %d\n", errno); 
  } 
  return 0;
}
                                              

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it's execv args:

execv("/bin/echo","echo","hello",NULL);                              // the trailing 0 is optional...

The first argument is the file, the next is argv[0]...
I'll try tonight, I have no linux at the current workplace.

According to LIBC:

 Function: int execv (const char *filename, char *const argv[])

This works a little better...
execl works as intended.
Your fread only read 1 , 1 byte block, now it return 14 (the echo string + \n).

#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <unistd.h>
#include <errno.h>
#include <stdlib.h> 
#define PIPE_PARENT 0
#define PIPE_CHILD 1 
int main (int argc, char *argv[])
{ 
  int channels[2]; 
  char mbr[512]; 
  pipe(channels); 
  pid_t pid = fork(); 
  if (pid == 0) { 
    // Child process, close parent's end.
    close (channels[PIPE_PARENT]); 
    // Close STDOUT
    close(1); 
    // Duplicate the child channel to STDOUT
    dup2(channels[PIPE_CHILD], 1); 
    // Close our old channel fd
    close(channels[PIPE_CHILD]);
    // Execute a file, hopefully anything it prints to STDOUT shoots straight through
    // our channel[PIPE_CHILD]
    execl("/bin/echo","echo","Test message!",NULL);
    exit(100);
  } else if (pid > 0) {
    FILE *f;
    // Parent, close childs end.
    close(channels[PIPE_CHILD]);
    // Open the parent's end
    f = fdopen(channels[PIPE_PARENT], "r");
    if (f == NULL) {
      printf("ERROR: Failed to open channel PIPE_PARENT, errno = %d\n", errno);
    } else {
      // Should read the char 'T'...
      printf("fread(PIPE_PARENT): %d, errno = %d\n", (int) fread(&mbr, 1, 512, f), errno);
      fclose(f);
    }
    close(channels[PIPE_PARENT]);
  } else {
    // Failure
    printf("ERROR: FORK Failed, errno = %d\n", errno);
  }
  return 0;
}
                                              

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Work well, if your UID/GID = 0....

If I su to a test user, it doesn't work which is what I require...

For a little more insight into the project,

I'm running Apache/PHP, I really don't want the apache/php process to have root privileges since it makes security so much more complicated!

I require a php script to call an executable that outputs data in a pre-defined format (Readable from my php script), but that executable requires root privileges to read the mbr of any given disk...

This is why sudo cannot work (Apache/PHP has no tty environment, sudo requires one).

Hope the context allows you to give me an alternate solution since the above, tho close, does not give me what I need.

Cheers,

KB.

ls -l of directory contents:

-rw-r--r-- 1 root root  258 2009-11-05 11:36 Makefile
-rwxr-xr-x 1 root root 6323 2009-11-10 18:58 printmbr
-rw-r--r-- 1 root root 1380 2009-11-10 18:58 printmbr.c
-rw-r--r-- 1 root root 1932 2009-11-10 18:58 printmbr.o
-rws--x--x 1 root root 5494 2009-11-05 22:43 readmbr
-rw-r--r-- 1 root root  843 2009-11-05 22:43 readmbr.c
-rw-r--r-- 1 root root 1364 2009-11-05 22:43 readmbr.o

Output of ./printmbr as user 'test'

[test@localhost printmbr]$ ./printmbr
Cannot open /dev/sda
fread(PIPE_PARENT): 0, errno = 29
Value = 0
Result = ''
[test@localhost printmbr]$



Is there something I'm missing?
Do I need to setuid() within readmbr?

WORKING!!!


Added some seteuid() code to readmbr... Presto!


Many thanks noci, much appreaciated.