[PATCH] libnetworking/rtems_dhcp.c: Fix improper hostname handling in DHCP request

[Aun-Ali Zaidi]

From: Tim Cussins <timcussins at eml.cc>

DHCP requests add the hostname option in dhcp_request_req() - this is cool, except that the dhcp
spec requires that this option has a length >= 1 char.
​
Excerpt taken from RFC 2132:

   3.14. Host Name Option

   This option specifies the name of the client.  The name may or may
   not be qualified with the local domain name (see section 3.17 for the
   preferred way to retrieve the domain name).  See RFC 1035 for
   character set restrictions.

   The code for this option is 12, and its minimum length is 1.

    Code   Len                 Host Name
   +-----+-----+-----+-----+-----+-----+-----+-----+--
   |  12 |  n  |  h1 |  h2 |  h3 |  h4 |  h5 |  h6 |  ...
   +-----+-----+-----+-----+-----+-----+-----+-----+--

At present, the hostname is added regardless. This appears to trigger a bug in a specific Netgear
router that causes it's dhcp process to lock up.

closes #1405.
---
 cpukit/libnetworking/rtems/rtems_dhcp.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/cpukit/libnetworking/rtems/rtems_dhcp.c b/cpukit/libnetworking/rtems/rtems_dhcp.c
index cb6966d..5b8fe32 100644
--- a/cpukit/libnetworking/rtems/rtems_dhcp.c
+++ b/cpukit/libnetworking/rtems/rtems_dhcp.c
@@ -681,10 +681,18 @@ dhcp_request_req (struct dhcp_packet* call,
   {
     if (gethostname (hostname, MAXHOSTNAMELEN) == 0)
     {
-      call->vend[len++] = DHCP_HOST;
-      call->vend[len++] = strlen (hostname);
-      strcpy ((char*) &call->vend[len], hostname);
-      len += strlen (hostname);
+      /* RFC 2132 Section 3.14 dictates min length for this option is 1 char.
+         If hostname is zero-length, then let's just not add it */
+
+      int hostnamelen = strlen(hostname);
+
+      if ( (hostnamelen > 0) && (hostnamelen < 256) )
+      {
+        call->vend[len++] = DHCP_HOST;
+	call->vend[len++] = (uint8_t) hostnamelen;
+	strcpy ((char *) &call->vend[len], hostname);
+	len += hostnamelen;
+      }
     }
     free (hostname, 0);
   }
-- 
2.1.4