su.c

#define LOG_TAG "su"
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <dirent.h>
#include <errno.h>
#include <unistd.h>
#include <time.h>
#include <pwd.h>
/*
 * SU can be given a specific command to exec. UID _must_ be
 * specified for this (ie argc => 3).
 *
 * Usage:
 * su 1000
 * su 1000 ls -l
 */
int main(int argc, char **argv)
{
    struct passwd *pw;
    int uid, gid, myuid;
    /* Until we have something better, only root and the shell can use su. */
    myuid = getuid();
    if(argc < 2) {
        uid = gid = 0;
    } else {
        pw = getpwnam(argv[1]);
        if(pw == 0) {
            uid = gid = atoi(argv[1]);
        } else {
            uid = pw->pw_uid;
            gid = pw->pw_gid;
        }
    }
    if(setgid(gid) || setuid(uid)) {
        printf("su: permission denied\n");
        return 1;
    }
    /* User specified command for exec. */
    if (argc == 3 ) {
        if (execlp(argv[2], argv[2], NULL) < 0) {
            printf("su: exec failed for %s Error:%s\n", argv[2],
                    strerror(errno));
            return -errno;
        }
    } else if (argc > 3) {
        /* Copy the rest of the args from main. */
        char *exec_args[argc - 1];
        memset(exec_args, 0, sizeof(exec_args));
        memcpy(exec_args, &argv[2], sizeof(exec_args));
        if (execvp(argv[2], exec_args) < 0) {
            printf("su: exec failed for %s Error:%s\n", argv[2],
                    strerror(errno));
            return -errno;
        }
    }
    /* Default exec shell. */
    execlp("/system/bin/sh", "sh", NULL);
    printf("su: exec failed\n");
    return 1;
}