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

[git]

commit fae9ca81a2eaf3534299b7ca3033b1e6605f9ab2
Author:     Michael Forney <mfor...@mforney.org>
AuthorDate: Sun Oct 23 20:59:51 2016 -0700
Commit:     Hiltjo Posthuma <hil...@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
@@ -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>
@@ -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)
 {
@@ -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;
@@ -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);
@@ -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);
@@ -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);