The Linux Programming Interface

810 Chapter 39

if (cap_free(empty) == -1)

return -1;

return s;

}

int

main(int argc, char *argv[])

{

char *username, *password, *encrypted, *p;

struct passwd *pwd;

struct spwd *spwd;

Boolean authOk;

size_t len;

long lnmax;

lnmax = sysconf(_SC_LOGIN_NAME_MAX);

if (lnmax == -1) /* If limit is indeterminate */

lnmax = 256; /* make a guess */

username = malloc(lnmax);

if (username == NULL)

errExit("malloc");

printf("Username: ");

fflush(stdout);

if (fgets(username, lnmax, stdin) == NULL)

exit(EXIT_FAILURE); /* Exit on EOF */

len = strlen(username);

if (username[len - 1] == '\n')

username[len - 1] = '\0'; /* Remove trailing '\n' */

pwd = getpwnam(username);

if (pwd == NULL)

fatal("couldn't get password record");

/* Only raise CAP_DAC_READ_SEARCH for as long as we need it */

if (raiseCap(CAP_DAC_READ_SEARCH) == -1)

fatal("raiseCap() failed");

spwd = getspnam(username);

if (spwd == NULL && errno == EACCES)

fatal("no permission to read shadow password file");

/* At this point, we won't need any more capabilities,

so drop all capabilities from all sets */

if (dropAllCaps() == -1)

fatal("dropAllCaps() failed");

if (spwd != NULL) /* If there is a shadow password record */

pwd->pw_passwd = spwd->sp_pwdp; /* Use the shadow password */