A Linux preloader to preempt logins for apps with 8 char dependencies

build64.sh

gcc -fPIC -rdynamic -g -c -Wall getpwuid_preload64.c
gcc -fPIC -rdynamic -g -c -Wall getlogin_preload64.c
gcc -shared -WI,-soname,libcpreload64.so.1 -o libcpreload64.so.1.0.1 getpwuid_preload64.o  getlogin_preload64.o -lc -ldl

getlogin_preload64.c

// Dan Wanek <[email protected]>
// This code was written to work around the 8 character login name issue
// with Natural and still allow users to have their Active Directory logins;
// which may in fact be longer than 8 characters.  Users are assigned a group
// in AD that is actually their old RACF mainframe login.  When logging in to
// Natural this library is called (vi LD_PRELOAD) and loads our own version of
// getpwuid which swaps out the real uid for the gid that has the same
// gidNumber as their uidNumber.  This is the RACF id.  Pretty sweet huh! :)
//
// Build:
//  gcc -fPIC -rdynamic -g -c -Wall getpwuid_preload64.c
//  gcc -shared -WI,-soname,libcpreload64.so.1 -o libcpreload64.so.1.0.1 getpwuid_preload64.o -lc -ldl
//
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <pwd.h>

#include "include/getpwuid_preload64.h"


char *getlogin(void) {
  char *login;
  struct passwd *pwent;
  uid_t uid;


  // Get the uid of the current process
  uid = getuid();
  pwent = sys_getpwuid(uid);
  if(!pwent) {
    if(errno == 0) {
      fputs("User does not exist.\n",stderr);
      exit(errno);
    } else {
      fputs("Error getting group: => ",stderr);
      char* err = strerror(errno);
      fputs(err,stderr);
      fputs("\n",stderr);
    }
    exit(errno);
  }

  login = pwent->pw_name;

  return(login);
}

getpwuid_preload64.c

// Dan Wanek <[email protected]>
// This code was written to work around the 8 character login name issue
// with Natural and still allow users to have their Active Directory logins;
// which may in fact be longer than 8 characters.  Users are assigned a group
// in AD that is actually their old RACF mainframe login.  When logging in to
// Natural this library is called (vi LD_PRELOAD) and loads our own version of
// getpwuid which swaps out the real uid for the gid that has the same
// gidNumber as their uidNumber.  This is the RACF id.  Pretty sweet huh! :)
//
// Build:
//  gcc -fPIC -rdynamic -g -c -Wall getpwuid_preload64.c
//  gcc -fPIC -rdynamic -g -c -Wall getlogin_preload64.c
//  gcc -shared -WI,-soname,libcpreload64.so.1 -o libcpreload64.so.1.0.1 getpwuid_preload64.o  getlogin_preload64.o -lc -ldl
//
#include "include/getpwuid_preload64.h"

struct passwd *sys_getpwuid(uid_t uid) {
  void *clib;
  struct passwd *(*sys_getpwuid)(uid_t);
  struct passwd *pass;

  clib = dlopen("/lib64/libnss_ldap.so.2",RTLD_LAZY);
  if(!clib) {
    fputs(dlerror(), stderr);
    exit(EXIT_FAILURE);
  }

  sys_getpwuid = dlsym(clib,"getpwuid");

  pass = sys_getpwuid(uid);

  return(pass);
}

struct passwd *getpwuid(uid_t uid) {
  struct passwd *pass;
  struct group *grp;

  pass = sys_getpwuid(uid);

  if(!pass) {
    fputs("Error: => ",stderr);
    char* err = strerror(errno);
    fputs(err,stderr);
    fputs("\n",stderr);

    exit(errno);
  }

  // Get the group struct where gidNumber == uidNumber (i.e. RACF login)
  grp = getgrgid(uid);
  if(!grp) {
    if(errno == 0) {
      fputs("RACF User does not exist.\n",stderr);
      exit(errno);
    } else {
      fputs("Error getting group: => ",stderr);
      char* err = strerror(errno);
      fputs(err,stderr);
      fputs("\n",stderr);
    }
    exit(errno);
  }


  // Parse RACF- from the gid name
  char *newpw_name;
  newpw_name = strdup(grp->gr_name);
  strsep(&newpw_name,"-");

  // Now do the swap.  Set the pw_name to the RACF id.
  pass->pw_name = newpw_name;

  return(pass);
}

getpwuid_preload64.h

#include <stdio.h>
#include <stdlib.h>
#include <dlfcn.h>
#include <sys/types.h>
#include <pwd.h>
#include <grp.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>

struct passwd *sys_getpwuid(uid_t uid);