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/*
* enter a password in the password file
* this program should be suid with owner
* with an owner with write permission on /etc/passwd
*/
#include <stdio.h>
#include <signal.h>
#include <pwd.h>

char    passwd[] = "/etc/passwd";
char    temp[]   = "/etc/ptmp";
struct  passwd *pwd;
struct  passwd *getpwent();
int     endpwent();
char    *strcpy();
char    *crypt();
char    *getpass();
char    *getlogin();
char    *pw;
char    pwbuf[10];
char    buf[512];

main(argc, argv)
char *argv[];
{
       char *p;
       int i;
       char saltc[2];
       long salt;
       int u,fi,fo;
       int insist;
       int ok, flags;
       int c;
       int pwlen;
       FILE *tf;
       char *uname;

       insist = 0;
       if(argc < 2) {
               if ((uname = getlogin()) == NULL) {
                       printf ("Usage: passwd user\n");
                       goto bex;
               } else {
                       printf("Changing password for %s\n", uname);
               }
       } else {
               uname = argv[1];
       }
       while(((pwd=getpwent()) != NULL)&&(strcmp(pwd->pw_name,uname)!=0));
       u = getuid();
       if((pwd==NULL) || (u!=0 && u != pwd->pw_uid))
               {
               printf("Permission denied.\n");
               goto bex;
               }
       endpwent();
       if (pwd->pw_passwd[0] && u != 0) {
               strcpy(pwbuf, getpass("Old password:"));
               pw = crypt(pwbuf, pwd->pw_passwd);
               if(strcmp(pw, pwd->pw_passwd) != 0) {
                       printf("Sorry.\n");
                       goto bex;
               }
       }
tryagn:
       strcpy(pwbuf, getpass("New password:"));
       pwlen = strlen(pwbuf);
       if (pwlen == 0) {
               printf("Password unchanged.\n");
               goto bex;
       }
       ok = 0;
       flags = 0;
       p = pwbuf;
       while(c = *p++){
               if(c>='a' && c<='z') flags |= 2;
               else if(c>='A' && c<='Z') flags |= 4;
               else if(c>='0' && c<='9') flags |= 1;
               else flags |= 8;
       }
       if(flags >=7 && pwlen>= 4) ok = 1;
       if(((flags==2)||(flags==4)) && pwlen>=6) ok = 1;
       if(((flags==3)||(flags==5)||(flags==6))&&pwlen>=5) ok = 1;

       if((ok==0) && (insist<2)){
               if(flags==1)
               printf("Please use at least one non-numeric character.\n");
               else
               printf("Please use a longer password.\n");
               insist++;
               goto tryagn;
               }

       if (strcmp(pwbuf,getpass("Retype new password:")) != 0) {
               printf ("Mismatch - password unchanged.\n");
               goto bex;
       }

       time(&salt);
       salt += getpid();

       saltc[0] = salt & 077;
       saltc[1] = (salt>>6) & 077;
       for(i=0;i<2;i++){
               c = saltc[i] + '.';
               if(c>'9') c += 7;
               if(c>'Z') c += 6;
               saltc[i] = c;
       }
       pw = crypt(pwbuf, saltc);
       signal(SIGHUP, SIG_IGN);
       signal(SIGINT, SIG_IGN);
       signal(SIGQUIT, SIG_IGN);

       if(access(temp, 0) >= 0) {
               printf("Temporary file busy -- try again\n");
               goto bex;
       }
       close(creat(temp,0600));
       if((tf=fopen(temp,"w")) == NULL) {
               printf("Cannot create temporary file\n");
               goto bex;
       }

/*
*      copy passwd to temp, replacing matching lines
*      with new password.
*/

       while((pwd=getpwent()) != NULL) {
               if(strcmp(pwd->pw_name,uname) == 0) {
                       u = getuid();
                       if(u != 0 && u != pwd->pw_uid) {
                               printf("Permission denied.\n");
                               goto out;
                       }
                       pwd->pw_passwd = pw;
               }
               fprintf(tf,"%s:%s:%d:%d:%s:%s:%s\n",
                       pwd->pw_name,
                       pwd->pw_passwd,
                       pwd->pw_uid,
                       pwd->pw_gid,
                       pwd->pw_gecos,
                       pwd->pw_dir,
                       pwd->pw_shell);
       }
       endpwent();
       fclose(tf);

/*
*      copy temp back to passwd file
*/

       if((fi=open(temp,0)) < 0) {
               printf("Temp file disappeared!\n");
               goto out;
       }
       if((fo=creat(passwd, 0644)) < 0) {
               printf("Cannot recreat passwd file.\n");
               goto out;
       }
       while((u=read(fi,buf,sizeof(buf))) > 0) write(fo,buf,u);

out:
       unlink(temp);

bex:
       exit(1);
}