r261913 broke DES passwords, because the only way they could work,

since they don't have an easily recognizable signature, was if they
were the default.  This commit rewrites crypt_set_format(3) etc to
address this:

 - Use a pointer instead of an index to identify the default format.
   This pointer is initialized at compile time to point to the first
   first element in the list of supported formats, eliminating the
   need for crypt_setdefault().  Using a pointer also simplifies
   iterating through the list.

 - Associate DES with the magic string "_", which takes care of the
   Extended DES format.

 - Finally, as a special case, if the salt does not match any known
   magic string but matches ^[./0-9A-Za-z]{13}$, it is assumed to be a
   DES password and is passed on to crypt_des().

MFC after:	1 week

1 files changed, 56 insertions, 77 deletions

diff --git a/lib/libcrypt/crypt.c b/lib/libcrypt/crypt.c
index ec4c7d0..040fdc1 100644
--- a/lib/libcrypt/crypt.c
+++ b/lib/libcrypt/crypt.c
@@ -1,6 +1,7 @@
-/*
- * Copyright (c) 1999
- *      Mark Murray.  All rights reserved.
+/*-
+ * Copyright (c) 1999 Mark Murray
+ * Copyright (c) 2014 Dag-Erling Smørgrav
+ * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
@@ -28,110 +29,88 @@
 __FBSDID("$FreeBSD$");
 
 #include <sys/types.h>
-#include <string.h>
+
 #include <libutil.h>
+#include <string.h>
 #include <unistd.h>
+
 #include "crypt.h"
 
-static const struct {
+/*
+ * List of supported crypt(3) formats.  The first element in the list will
+ * be the default.
+ */
+static const struct crypt_format {
 	const char *const name;
 	char *(*const func)(const char *, const char *);
 	const char *const magic;
-} crypt_types[] = {
-#ifdef HAS_DES
-	{
-		"des",
-		crypt_des,
-		NULL
-	},
-#endif
-	{
-		"md5",
-		crypt_md5,
-		"$1$"
-	},
+} crypt_formats[] = {
+	/* default format */
+	{ "sha512",	crypt_sha512,		"$6$"	},
+
+	/* other supported formats */
+	{ "md5",	crypt_md5,		"$1$"	},
 #ifdef HAS_BLOWFISH
-	{
-		"blf",
-		crypt_blowfish,
-		"$2"
-	},
+	{ "blf",	crypt_blowfish,		"$2"	},
+#endif
+	{ "nth",	crypt_nthash,		"$3$"	},
+	{ "sha256",	crypt_sha256,		"$5$"	},
+#ifdef HAS_DES
+	{ "des",	crypt_des,		"_"	},
 #endif
-	{
-		"nth",
-		crypt_nthash,
-		"$3$"
-	},
-	{
-		"sha256",
-		crypt_sha256,
-		"$5$"
-	},
-	{
-		"sha512",
-		crypt_sha512,
-		"$6$"
-	},
-	{
-		NULL,
-		NULL,
-		NULL
-	}
-};
-
-#define CRYPT_DEFAULT	"sha512"
 
-static int crypt_type = -1;
+	/* sentinel */
+	{ NULL,		NULL,			NULL	}
+};
 
-static void
-crypt_setdefault(void)
-{
-	size_t i;
+static const struct crypt_format *crypt_format = &crypt_formats[0];
 
-	if (crypt_type != -1)
-		return;
-	for (i = 0; i < sizeof(crypt_types) / sizeof(crypt_types[0]) - 1; i++) {
-		if (strcmp(CRYPT_DEFAULT, crypt_types[i].name) == 0) {
-			crypt_type = (int)i;
-			return;
-		}
-	}
-	crypt_type = 0;
-}
+#define DES_SALT_ALPHABET \
+	"./0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
 
+/*
+ * Returns the name of the currently selected format.
+ */
 const char *
 crypt_get_format(void)
 {
 
-	crypt_setdefault();
-	return (crypt_types[crypt_type].name);
+	return (crypt_format->name);
 }
 
+/*
+ * Selects the format to use for subsequent crypt(3) invocations.
+ */
 int
-crypt_set_format(const char *type)
+crypt_set_format(const char *format)
 {
-	size_t i;
+	const struct crypt_format *cf;
 
-	crypt_setdefault();
-	for (i = 0; i < sizeof(crypt_types) / sizeof(crypt_types[0]) - 1; i++) {
-		if (strcmp(type, crypt_types[i].name) == 0) {
-			crypt_type = (int)i;
+	for (cf = crypt_formats; cf->name != NULL; ++cf) {
+		if (strcasecmp(cf->name, format) == 0) {
+			crypt_format = cf;
 			return (1);
 		}
 	}
 	return (0);
 }
 
+/*
+ * Hash the given password with the given salt.  If the salt begins with a
+ * magic string (e.g. "$6$" for sha512), the corresponding format is used;
+ * otherwise, the currently selected format is used.
+ */
 char *
 crypt(const char *passwd, const char *salt)
 {
-	size_t i;
+	const struct crypt_format *cf;
 
-	crypt_setdefault();
-	for (i = 0; i < sizeof(crypt_types) / sizeof(crypt_types[0]) - 1; i++) {
-		if (crypt_types[i].magic != NULL && strncmp(salt,
-		    crypt_types[i].magic, strlen(crypt_types[i].magic)) == 0)
-			return (crypt_types[i].func(passwd, salt));
-	}
-	return (crypt_types[crypt_type].func(passwd, salt));
+	for (cf = crypt_formats; cf->name != NULL; ++cf)
+		if (cf->magic != NULL && strstr(salt, cf->magic) == salt)
+			return (cf->func(passwd, salt));
+#ifdef HAS_DES
+	if (strlen(salt) == 13 && strspn(salt, DES_SALT_ALPHABET) == 13)
+		return (crypt_des(passwd, salt));
+#endif
+	return (crypt_format->func(passwd, salt));
 }