[Dnsmasq-discuss] [PATCH 1/1] dhcp protocol: adding long options support (rfc3396)

[Peter Kaestle]

When the value length of an option exceeds 255 bytes, split it into a
second option with same option id, following rfc3396.

Signed-off-by: Peter Kaestle <peter.kaestle at nokia.com>
---
 src/dhcp-protocol.h |  5 ++++-
 src/rfc2131.c       | 22 +++++++++++++++++-----
 2 files changed, 21 insertions(+), 6 deletions(-)

diff --git a/src/dhcp-protocol.h b/src/dhcp-protocol.h
index 3dde354..faf1b2b 100644
--- a/src/dhcp-protocol.h
+++ b/src/dhcp-protocol.h
@@ -92,11 +92,14 @@
 
 #define DHCP_CHADDR_MAX 16
 
+#define MAX_OPTION_BUFF_SIZE 3000
+#define MAX_OPTION_SIZE 255
+
 struct dhcp_packet {
   u8 op, htype, hlen, hops;
   u32 xid;
   u16 secs, flags;
   struct in_addr ciaddr, yiaddr, siaddr, giaddr;
   u8 chaddr[DHCP_CHADDR_MAX], sname[64], file[128];
-  u8 options[312];
+  u8 options[MAX_OPTION_BUFF_SIZE];
 };
diff --git a/src/rfc2131.c b/src/rfc2131.c
index 68834ea..b428c40 100644
--- a/src/rfc2131.c
+++ b/src/rfc2131.c
@@ -1979,13 +1979,25 @@ static void option_put_string(struct dhcp_packet *mess, unsigned char *end, int
 			      const char *string, int null_term)
 {
   unsigned char *p;
-  size_t len = strlen(string);
-
-  if (null_term && len != 255)
+ /* using signed int here to detect if length is shorter than MAX_OPTION_SIZE */
+  int len = strlen(string);
+
+  /*
+   * if string is not terminated, add one byte for termination
+   *  - don't do that in case data fits exactly in 255 bytes of one option
+   */
+  if (null_term && len % MAX_OPTION_SIZE)
     len++;
 
-  if ((p = free_space(mess, end, opt, len)))
-    memcpy(p, string, len);
+  /* if option data length is bigger than 255, split it like specified in rfc3396 */
+  for (; len > 0; len -= MAX_OPTION_SIZE, string += MAX_OPTION_SIZE) {
+    size_t l = len >= MAX_OPTION_SIZE ? MAX_OPTION_SIZE : len;
+
+    if ((p = free_space(mess, end, opt, l)))
+      memcpy(p, string, l);
+    else
+      break;
+  }
 }
 
 /* return length, note this only does the data part */
-- 
2.45.0