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passwd: Use a random salt when encrypting passwords

This commit is contained in:
Michael Forney 2016-10-23 20:59:51 -07:00 committed by Hiltjo Posthuma
parent 3a5939e810
commit fae9ca81a2
1 changed files with 33 additions and 6 deletions
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39
passwd.c
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@ -2,12 +2,14 @@
#include <sys/ioctl.h> #include <sys/ioctl.h>
#include <sys/stat.h> #include <sys/stat.h>
#include <sys/types.h> #include <sys/types.h>
#include <sys/syscall.h>
#include <errno.h> #include <errno.h>
#include <fcntl.h> #include <fcntl.h>
#include <limits.h> #include <limits.h>
#include <pwd.h> #include <pwd.h>
#include <shadow.h> #include <shadow.h>
#include <stdint.h>
#include <stdio.h> #include <stdio.h>
#include <stdlib.h> #include <stdlib.h>
#include <string.h> #include <string.h>
@ -127,6 +129,27 @@ cleanup:
return r; return r;
} }
/* generates a random base64-encoded salt string of length 16 */
static void
gensalt(char *s)
{
static const char b64[] = "./0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
uint8_t buf[12];
uint32_t n;
int i;
if (syscall(SYS_getrandom, buf, sizeof(buf), 0) < 0)
eprintf("getrandom:");
for (i = 0; i < 12; i += 3) {
n = buf[i] << 16 | buf[i+1] << 8 | buf[i+2];
*s++ = b64[n%64]; n /= 64;
*s++ = b64[n%64]; n /= 64;
*s++ = b64[n%64]; n /= 64;
*s++ = b64[n];
}
*s++ = '\0';
}
static void static void
usage(void) usage(void)
{ {
@ -137,7 +160,7 @@ int
main(int argc, char *argv[]) main(int argc, char *argv[])
{ {
char *cryptpass1 = NULL, *cryptpass2 = NULL, *cryptpass3 = NULL; char *cryptpass1 = NULL, *cryptpass2 = NULL, *cryptpass3 = NULL;
char *inpass, *p, *salt = PW_CIPHER, *prevhash = NULL; char *inpass, *p, *prevhash = NULL, salt[sizeof(PW_CIPHER) + 16] = PW_CIPHER;
struct passwd *pw; struct passwd *pw;
struct spwd *spw = NULL; struct spwd *spw = NULL;
FILE *fp = NULL; FILE *fp = NULL;
@ -188,9 +211,9 @@ main(int argc, char *argv[])
goto newpass; goto newpass;
} }
if (pw->pw_passwd[0] == 'x') if (pw->pw_passwd[0] == 'x')
prevhash = salt = spw->sp_pwdp; prevhash = spw->sp_pwdp;
else else
prevhash = salt = pw->pw_passwd; prevhash = pw->pw_passwd;
} }
printf("Changing password for %s\n", pw->pw_name); printf("Changing password for %s\n", pw->pw_name);
@ -199,7 +222,7 @@ main(int argc, char *argv[])
eprintf("getpass:"); eprintf("getpass:");
if (inpass[0] == '\0') if (inpass[0] == '\0')
eprintf("no password supplied\n"); eprintf("no password supplied\n");
p = crypt(inpass, salt); p = crypt(inpass, prevhash);
if (!p) if (!p)
eprintf("crypt:"); eprintf("crypt:");
cryptpass1 = estrdup(p); cryptpass1 = estrdup(p);
@ -212,12 +235,16 @@ newpass:
eprintf("getpass:"); eprintf("getpass:");
if (inpass[0] == '\0') if (inpass[0] == '\0')
eprintf("no password supplied\n"); eprintf("no password supplied\n");
p = crypt(inpass, prevhash);
if (!p)
eprintf("crypt:");
if (cryptpass1 && strcmp(cryptpass1, p) == 0)
eprintf("password left unchanged\n");
gensalt(salt + strlen(salt));
p = crypt(inpass, salt); p = crypt(inpass, salt);
if (!p) if (!p)
eprintf("crypt:"); eprintf("crypt:");
cryptpass2 = estrdup(p); cryptpass2 = estrdup(p);
if (cryptpass1 && strcmp(cryptpass1, cryptpass2) == 0)
eprintf("password left unchanged\n");
/* Flush pending input */ /* Flush pending input */
ioctl(0, TCFLSH, (void *)0); ioctl(0, TCFLSH, (void *)0);