[hackers] [ubase] passwd: Use a random salt when encrypting passwords || Michael Forney

From: <git_AT_suckless.org>
Date: Tue, 22 Aug 2017 13:40:05 +0200 (CEST)

commit fae9ca81a2eaf3534299b7ca3033b1e6605f9ab2
Author: Michael Forney <mforney_AT_mforney.org>
AuthorDate: Sun Oct 23 20:59:51 2016 -0700
Commit: Hiltjo Posthuma <hiltjo_AT_codemadness.org>
CommitDate: Tue Aug 22 13:36:56 2017 +0200

    passwd: Use a random salt when encrypting passwords

diff --git a/passwd.c b/passwd.c
index 3ea3dd1..52b70a8 100644
--- a/passwd.c
+++ b/passwd.c
_AT_@ -2,12 +2,14 @@
 #include <sys/ioctl.h>
 #include <sys/stat.h>
 #include <sys/types.h>
+#include <sys/syscall.h>
 
 #include <errno.h>
 #include <fcntl.h>
 #include <limits.h>
 #include <pwd.h>
 #include <shadow.h>
+#include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
_AT_@ -127,6 +129,27 @@ cleanup:
         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
 usage(void)
 {
_AT_@ -137,7 +160,7 @@ int
 main(int argc, char *argv[])
 {
         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 spwd *spw = NULL;
         FILE *fp = NULL;
_AT_@ -188,9 +211,9 @@ main(int argc, char *argv[])
                         goto newpass;
                 }
                 if (pw->pw_passwd[0] == 'x')
- prevhash = salt = spw->sp_pwdp;
+ prevhash = spw->sp_pwdp;
                 else
- prevhash = salt = pw->pw_passwd;
+ prevhash = pw->pw_passwd;
         }
 
         printf("Changing password for %s\n", pw->pw_name);
_AT_@ -199,7 +222,7 @@ main(int argc, char *argv[])
                 eprintf("getpass:");
         if (inpass[0] == '\0')
                 eprintf("no password supplied\n");
- p = crypt(inpass, salt);
+ p = crypt(inpass, prevhash);
         if (!p)
                 eprintf("crypt:");
         cryptpass1 = estrdup(p);
_AT_@ -212,12 +235,16 @@ newpass:
                 eprintf("getpass:");
         if (inpass[0] == '\0')
                 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);
         if (!p)
                 eprintf("crypt:");
         cryptpass2 = estrdup(p);
- if (cryptpass1 && strcmp(cryptpass1, cryptpass2) == 0)
- eprintf("password left unchanged\n");
 
         /* Flush pending input */
         ioctl(0, TCFLSH, (void *)0);
Received on Tue Aug 22 2017 - 13:40:05 CEST