dhcp: distinguish malformed and truncated options

This patch distinguishes malformed DHCP options from truncated ones.
Previously, the malformed_options field was never set, causing all option
parsing failures to be reported as truncated.

Ticket OISF#8874

Author: glongo

rust/src/dhcp/parser.rs

@@ -21,7 +21,7 @@ use crate::dhcp::dhcp::*;
 use nom8::bytes::streaming::take;
 use nom8::combinator::verify;
 use nom8::number::streaming::{be_u16, be_u32, be_u8};
-use nom8::{IResult, Parser};
+use nom8::{Err, IResult, Parser};
 
 pub struct DHCPMessage {
     pub header: DHCPHeader,
@@ -242,7 +242,7 @@ pub fn parse_dhcp(input: &[u8]) -> IResult<&[u8], DHCPMessage> {
         Ok((rem, header)) => {
             let mut options = Vec::new();
             let mut next = rem;
-            let malformed_options = false;
+            let mut malformed_options = false;
             let mut truncated_options = false;
             loop {
                 match parse_option(next) {
@@ -254,10 +254,14 @@ pub fn parse_dhcp(input: &[u8]) -> IResult<&[u8], DHCPMessage> {
                             break;
                         }
                     }
-                    Err(_) => {
+                    Err(Err::Incomplete(_)) => {
                         truncated_options = true;
                         break;
                     }
+                    Err(Err::Error(_)) | Err(Err::Failure(_)) => {
+                        malformed_options = true;
+                        break;
+                    }
                 }
             }
             let overload = find_overload_value(&options);