CODEWITHSUNDEEP
clinuxchange-password
SVC1
SVC1

Reputation: 39

Changing Password using popen() in C code

I am trying to change the password in C Code using popen.

On the Linux I have, on command prompt, passwd (busybox) works fine

    # passwd simon
    Changing password for simon
    New password:
    Retype password:
    Password for simon changed by root

I am trying to do this within C (running as root):

int len=strlen(s_password); char line[1024];
sprintf(line,"passwd  %s", s_username);
FILE *fp= popen(line,"w");

int i;
for(i=0; i<len;++i)fputc(s_password[i], fp);
for(i=0; i<len;++i)fputc(s_password[i], fp);
fputc('\n', fp);

//fprintf(fp,"%s\n",s_password);
//fprintf(fp,"%s",s_password);
pclose(fp);

I tried also fprintf (commented) but without success. Seems like the first entry is passing but not the second. When I execute the code, I get:

     Changing password for simon
     New password:
     Retype password:
     passwd: password for simon is unchanged

I tried all possible scenarios (with '\n' omitting '\n') without success.

As if the 'Retype password' is different than the 'New password'.

What am I doing wrong?

Upvotes: 1

Views: 2416

Answers (2)

L&#225;szl&#243; Papp
L&#225;szl&#243; Papp

Reputation: 53155

This util works fine for me:

main.c

#include <stdio.h>
#include <sys/wait.h>

int main(int argc, char **argv)
{
    if (argc < 3) {
        printf("Usage: %s username password\n", argv[0]);
        return 1;
    }
    char cmd[32];
    sprintf(cmd, " passwd %s", argv[1]);
    FILE *fp= popen(cmd, "w");
    fprintf(fp, "%s\n", argv[2]);
    fprintf(fp, "%s\n", argv[2]);
    printf("Return value: %i\n", WEXITSTATUS(pclose(fp)));
    return 0;
}

Build

gcc -Wall -Wpedantic -Wextra main.c

Upvotes: 3

Ferenc Deak
Ferenc Deak

Reputation: 35408

I think you should write to fileno(fp) instead of simple fp. That is your end of the pipe if I understood correctly the docs: http://linux.die.net/man/3/fileno and http://pubs.opengroup.org/onlinepubs/009696699/functions/popen.html

Upvotes: 2

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