dhcpc: code shrink in good_hostname

Incorporated valid_domain_label into good_hostname to simplify the implementation.

function                                             old     new   delta
static.xmalloc_optname_optval                        973     958     -15
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-15)             Total: -15 bytes
   text	   data	    bss	    dec	    hex	filename
 993144	  16915	   1872	1011931	  f70db	busybox_old
 993129	  16915	   1872	1011916	  f70cc	busybox_unstripped

Signed-off-by: Martin Lewis <martin.lewis.x84@gmail.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 14 insertions, 48 deletions

diff --git a/networking/udhcp/dhcpc.c b/networking/udhcp/dhcpc.c
index 5a1f8fd7a..6422181da 100644
--- a/networking/udhcp/dhcpc.c
+++ b/networking/udhcp/dhcpc.c
@@ -159,61 +159,27 @@ static int mton(uint32_t mask)
 }
 
 #if ENABLE_FEATURE_UDHCPC_SANITIZEOPT
-/* Check if a given label represents a valid DNS label
- * Return pointer to the first character after the label
- * (NUL or dot) upon success, NULL otherwise.
- * See RFC1035, 2.3.1
- */
+/* Check if a given name represents a valid DNS name */
+/* See RFC1035, 2.3.1 */
 /* We don't need to be particularly anal. For example, allowing _, hyphen
  * at the end, or leading and trailing dots would be ok, since it
- * can't be used for attacks. (Leading hyphen can be, if someone uses
- * cmd "$hostname"
+ * can't be used for attacks. (Leading hyphen can be, if someone uses cmd "$hostname"
  * in the script: then hostname may be treated as an option)
  */
-static const char *valid_domain_label(const char *label)
-{
-        unsigned char ch;
-        //unsigned pos = 0;
-
-        if (label[0] == '-')
-                return NULL;
-        for (;;) {
-                ch = *label;
-                if ((ch|0x20) < 'a' || (ch|0x20) > 'z') {
-                        if (ch < '0' || ch > '9') {
-                                if (ch == '\0' || ch == '.')
-                                        return label;
-                                /* DNS allows only '-', but we are more permissive */
-                                if (ch != '-' && ch != '_')
-                                        return NULL;
-                        }
-                }
-                label++;
-                //pos++;
-                //Do we want this?
-                //if (pos > 63) /* NS_MAXLABEL; labels must be 63 chars or less */
-                //      return NULL;
-        }
-}
-
-/* Check if a given name represents a valid DNS name */
-/* See RFC1035, 2.3.1 */
 static int good_hostname(const char *name)
 {
-        //const char *start = name;
-
-        for (;;) {
-                name = valid_domain_label(name);
-                if (!name)
-                        return 0;
-                if (!name[0])
-                        return 1;
-                        //Do we want this?
-                        //return ((name - start) < 1025); /* NS_MAXDNAME */
-                name++;
-                if (*name == '\0')
-                        return 1; // We allow trailing dot too
+        if (*name == '-') /* Can't start with '-' */
+                return 0;
+
+        while (*name) {
+                unsigned char ch = *name++;
+                if (!isalnum(ch))
+                        /* DNS allows only '-', but we are more permissive */
+                        if (ch != '-' && ch != '_' && ch != '.')
+                                return 0;
+                // TODO: do we want to validate lengths against NS_MAXLABEL and NS_MAXDNAME?
         }
+        return 1;
 }
 #else
 # define good_hostname(name) 1