2 files changed, 42 insertions, 4 deletions

diff --git a/auth-passwd.c b/auth-passwd.c
index 63ccf3cab..530b5d4f7 100644
--- a/auth-passwd.c
+++ b/auth-passwd.c
@@ -193,7 +193,7 @@ int
 sys_auth_passwd(Authctxt *authctxt, const char *password)
 {
         struct passwd *pw = authctxt->pw;
-        char *encrypted_password;
+        char *encrypted_password, *salt = NULL;
 
         /* Just use the supplied fake password if authctxt is invalid */
         char *pw_password = authctxt->valid ? shadow_pw(pw) : pw->pw_passwd;
@@ -202,9 +202,13 @@ sys_auth_passwd(Authctxt *authctxt, const char *password)
         if (strcmp(pw_password, "") == 0 && strcmp(password, "") == 0)
                 return (1);
 
-        /* Encrypt the candidate password using the proper salt. */
-        encrypted_password = xcrypt(password,
-            (pw_password[0] && pw_password[1]) ? pw_password : "xx");
+        /*
+         * Encrypt the candidate password using the proper salt, or pass a
+         * NULL and let xcrypt pick one.
+         */
+        if (authctxt->valid && pw_password[0] && pw_password[1])
+                salt = pw_password;
+        encrypted_password = xcrypt(password, salt);
 
         /*
          * Authentication is accepted if the encrypted passwords
diff --git a/openbsd-compat/xcrypt.c b/openbsd-compat/xcrypt.c
index 8577cbd8a..8913bb81a 100644
--- a/openbsd-compat/xcrypt.c
+++ b/openbsd-compat/xcrypt.c
@@ -25,6 +25,7 @@
 #include "includes.h"
 
 #include <sys/types.h>
+#include <string.h>
 #include <unistd.h>
 #include <pwd.h>
 
@@ -62,11 +63,44 @@
 #  define crypt DES_crypt
 # endif
 
+/*
+ * Pick an appropriate password encryption type and salt for the running
+ * system.
+ */
+static const char *
+pick_salt(void)
+{
+        struct passwd *pw;
+        char *passwd, *p;
+        size_t typelen;
+        static char salt[32];
+
+        if (salt[0] != '\0')
+                return salt;
+        strlcpy(salt, "xx", sizeof(salt));
+        if ((pw = getpwuid(0)) == NULL)
+                return salt;
+        passwd = shadow_pw(pw);
+        if (passwd[0] != '$' || (p = strrchr(passwd + 1, '$')) == NULL)
+                return salt;  /* no $, DES */
+        typelen = p - passwd + 1;
+        strlcpy(salt, passwd, MIN(typelen, sizeof(salt)));
+        explicit_bzero(passwd, strlen(passwd));
+        return salt;
+}
+
 char *
 xcrypt(const char *password, const char *salt)
 {
         char *crypted;
 
+        /*
+         * If we don't have a salt we are encrypting a fake password for
+         * for timing purposes.  Pick an appropriate salt.
+         */
+        if (salt == NULL)
+                salt = pick_salt();
+
 # ifdef HAVE_MD5_PASSWORDS
         if (is_md5_salt(salt))
                 crypted = md5_crypt(password, salt);