feat(net): Parse payload for ICMP

ICMP Error messages (such as "Destination Unreachable") may contain a
payload, made of a full or truncated version of the original IP packet
that triggered the error. Parse this packet using the existing
EmbeddedHeaders structure added in previous commits.

Signed-off-by: Quentin Monnet <[email protected]>

Author: qmonnet

net/src/headers/mod.rs

@@ -300,8 +300,10 @@ impl ParsePayload for Header {
                     None
                 }
             }
+            Icmp4(icmp4) => icmp4.parse_payload(cursor).map(Header::from),
+            Icmp6(icmp6) => icmp6.parse_payload(cursor).map(Header::from),
             Udp(udp) => udp.parse_payload(cursor).map(Header::from),
-            Encap(_) | Tcp(_) | Icmp4(_) | Icmp6(_) | EmbeddedIp(_) => None,
+            Encap(_) | Tcp(_) | EmbeddedIp(_) => None,
         }
     }
 }

net/src/icmp4/mod.rs

@@ -3,13 +3,15 @@
 
 //! `ICMPv4` header type and logic.
 
-use crate::parse::{DeParse, DeParseError, IntoNonZeroUSize, LengthError, Parse, ParseError};
-use etherparse::{Icmpv4Header, Icmpv4Type};
-
 mod checksum;
 
 pub use checksum::*;
 
+use crate::headers::{EmbeddedHeaders, EmbeddedIpVersion};
+use crate::parse::{
+    DeParse, DeParseError, IntoNonZeroUSize, LengthError, Parse, ParseError, ParseWith, Reader,
+};
+use etherparse::{Icmpv4Header, Icmpv4Type};
 use std::{net::IpAddr, num::NonZero};
 
 #[allow(unused_imports)] // re-export
@@ -127,6 +129,16 @@ impl Icmp4 {
             checksum: 0,
         })
     }
+
+    pub(crate) fn parse_payload(&self, cursor: &mut Reader) -> Option<EmbeddedHeaders> {
+        if !self.is_error_message() {
+            return None;
+        }
+        let (headers, consumed) =
+            EmbeddedHeaders::parse_with(EmbeddedIpVersion::Ipv4, cursor.inner).ok()?;
+        cursor.consume(consumed).ok()?;
+        Some(headers)
+    }
 }
 
 impl Parse for Icmp4 {

net/src/icmp6/mod.rs

@@ -7,7 +7,10 @@ mod checksum;
 
 pub use checksum::*;
 
-use crate::parse::{DeParse, DeParseError, IntoNonZeroUSize, LengthError, Parse, ParseError};
+use crate::headers::{EmbeddedHeaders, EmbeddedIpVersion};
+use crate::parse::{
+    DeParse, DeParseError, IntoNonZeroUSize, LengthError, Parse, ParseError, ParseWith, Reader,
+};
 use etherparse::{Icmpv6Header, Icmpv6Type};
 use std::num::NonZero;
 
@@ -31,6 +34,26 @@ impl Icmp6 {
         &mut self.0.icmp_type
     }
 
+    /// Returns true if the ICMP type is an error message
+    #[must_use]
+    pub fn is_error_message(&self) -> bool {
+        // List all types to make it sure we catch any new addition to the enum
+        match self.icmp_type() {
+            Icmpv6Type::DestinationUnreachable(_)
+            | Icmpv6Type::PacketTooBig { .. }
+            | Icmpv6Type::TimeExceeded(_)
+            | Icmpv6Type::ParameterProblem(_) => true,
+            Icmpv6Type::Unknown { .. }
+            | Icmpv6Type::EchoRequest(_)
+            | Icmpv6Type::EchoReply(_)
+            | Icmpv6Type::RouterSolicitation
+            | Icmpv6Type::RouterAdvertisement(_)
+            | Icmpv6Type::NeighborSolicitation
+            | Icmpv6Type::NeighborAdvertisement(_)
+            | Icmpv6Type::Redirect => false,
+        }
+    }
+
     /// Creates a new `Icmp6` with the given type.
     ///
     /// The checksum will be set to zero.
@@ -41,6 +64,16 @@ impl Icmp6 {
             checksum: 0,
         })
     }
+
+    pub(crate) fn parse_payload(&self, cursor: &mut Reader) -> Option<EmbeddedHeaders> {
+        if !self.is_error_message() {
+            return None;
+        }
+        let (headers, consumed) =
+            EmbeddedHeaders::parse_with(EmbeddedIpVersion::Ipv6, cursor.inner).ok()?;
+        cursor.consume(consumed).ok()?;
+        Some(headers)
+    }
 }
 
 impl Parse for Icmp6 {

net/src/parse.rs

@@ -151,7 +151,7 @@ impl Reader<'_> {
         })
     }
 
-    fn consume(&mut self, n: NonZero<u16>) -> Result<(), LengthError> {
+    pub(crate) fn consume(&mut self, n: NonZero<u16>) -> Result<(), LengthError> {
         if n.get() > self.remaining {
             return Err(LengthError {
                 expected: n.into_non_zero_usize(),