根SUID C包装器调试

Question

I am new to C and this is a simple wrapper I wrote to run execute scripts as different user. I understand I can do visudo in etc/sudoers but, I already did this and I don't want it to go to waste, also it will help me improve writing in C. I seem to ha The problem is I am having errors when I compile it. My operating system is Ubuntu 12.04.03 LTS. Can someone help me fix these errors?

rootsuidwrapper.c: In function ‘trusted’:
rootsuidwrapper.c:60:15: warning: assignment makes pointer from integer without a cast [enabled by default]
rootsuidwrapper.c: In function ‘main’:
rootsuidwrapper.c:116:48: error: too many arguments to function ‘stat’
/usr/include/x86_64-linux-gnu/sys/stat.h:211:12: note: declared here

It would be nice if someone could fix these errors and give me the working code. Also, I would like to know what I did wrong.

 * This program must be run as root to work.
 */

#if !defined(lint) && !defined(SABER) || defined(RCS_HDRS)
#endif /* !lint && !SABER || RCS_HDRS */
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <netdb.h>
#include <sys/stat.h>

#define TRUSTED_GROUP "trusted"

typedef enum { false = 0, true } bool;

#ifdef __STDC__
bool trusted(char *whoami)
#else
bool trusted(whoami)
  char *whoami;
#endif /* __STDC__ */
{
    char *user;
    char host[BUFSIZ + 1];
    char domain[BUFSIZ + 1];
    struct hostent *hp;

    /* 
     * Figure out whether this user on this host in this domain is
     * trusted.
     */

    /* 
     * Determine our domain name
     */
    (void) memset(domain, '\0', sizeof(domain));
    getdomainname(domain, sizeof(domain) - 1);

    /* 
     * Figure out our fully canonicalized hostname
     */

    (void) memset(host, '\0', sizeof(host));
    gethostname(host, sizeof(host) - 1);
    if ((hp = gethostbyname(host)) == NULL) {
    strcat(host, ".");
    strcat(host, domain);
    fprintf(stderr, 
        "%s: WARNING: can't canonlicalize hostname; assuming %s.\n",
        whoami, host);
    }
    else {
    strcpy(host, hp->h_name);
    }

    /* 
     * Get login name of current user
     */
    if ((user = cuserid(NULL)) == NULL) {
    fprintf(stderr, " %s: You do not seem to be in the passwd file!\n",
        whoami);
    return(false);
    }

    /* 
     * Look this triple up in the trusted netgroup 
     */

    return ((innetgr(TRUSTED_GROUP, host, user, domain) == 1) ? true : false);
}


#ifdef __STDC__
main(int argc, char *argv[])
#else
main(argc, argv)
  int argc;
  char *argv[];
#endif /* __STDC__ */
{
    char *whoami;
    int ouruid;         /* uid we set to run chown and chmod */
    int proguid;        /* uid we are chowning program to */
    char *filename;
    struct stat statbuf;
    int error = 0;

    if (whoami = strrchr(argv[0], '/')) 
    whoami ++;
    else
    whoami = argv[0];

    if (argc == 3)
    proguid = atoi(argv[2]);
    else if (argc == 2)
    proguid = 0;
    else {
    fprintf(stderr, "usage: %s filename [proguid]\n", whoami);
    exit(1);
    }

    filename = argv[1];

    if (trusted(whoami)) 
    ouruid = 0;
    else
    ouruid = getuid();

    if (setuid(ouruid) == -1) {
    fprintf(stderr, "%s: Warning: setuid(%d) failed: ", whoami, ouruid);
    perror(NULL);
    exit(1);
    }

    if (stat(filename, &statbuf, sizeof(struct stat)) == -1) {
    fprintf(stderr, "%s: failure statting %s: ", whoami, filename);
    perror(NULL);
    exit(1);
    }

    if (chown(filename, proguid, -1) == -1) {
    error++;
    fprintf(stderr, "%s: chown %d %s failed: ", whoami, proguid, filename);
    perror(NULL);
    fprintf(stderr, "continuing...\n");
    }

    if (chmod(filename, statbuf.st_mode | S_ISUID)) {
    error++;
    fprintf(stderr, "%s: chmod u+s %s failed: ", whoami, filename);
    perror(NULL);
    }

    return(error);
}

Help is appreciated,

Answer 1

NAME
       stat, fstat, lstat - get file status

SYNOPSIS
       #include <sys/types.h>
       #include <sys/stat.h>
       #include <unistd.h>

       int stat(const char *path, struct stat *buf);
       int fstat(int filedes, struct stat *buf);
       int lstat(const char *path, struct stat *buf);

Remove your third parameter in the call to stat(). Your code should then be:

if (stat(filename, &statbuf) == -1) {

There is no need to tell stat() the size of the buffer because stat() expects a struct stat * which has a fixed size.

Answer 2

For the compiler warning:

cuserid() returns a pointer to a character ( char* ). When any function returns a pointer, and you want to place the return value into a buffer, then you have to put the return value into a specific place in the buffer, usually the beginning. Specifically, you should use:

*user = cuserid(NULL);
if(user == NULL)

Remember, cuserid() returns a pointer to a single character. Therefore, the return value of the function should go into a single character - that is, *user or user[0] . When the above code is used, the compiler shouldn't complain. Then you place the result of cuserid(NULL) into user , from the first byte to the rest of the memory allocated.