Add support for IP_RECVERR and IPV6_RECVERR

Setting these options enables receiving errors, such as ICMP errors from
the network, via `recvmsg()` with `MSG_ERRQUEUE`.

Adds new `Ipv{4,6}RecvErr` variants to `ControlMessageOwned`.  These
control messages are produced when `Ipv4RecvErr` or `Ipv6RecvErr`
options are enabled on a raw or datagram socket.

New tests for the functionality can be run with `cargo test --test test
test_recverr`.

This commit builds on an earlier draft of the functionality authored by
Matthew McPherrin <git@mcpherrin.ca>.

2 files changed, 39 insertions, 0 deletions

diff --git a/src/sys/socket/mod.rs b/src/sys/socket/mod.rs
index 33585bb9..50d8b6fb 100644
--- a/src/sys/socket/mod.rs
+++ b/src/sys/socket/mod.rs
@@ -653,6 +653,13 @@ pub enum ControlMessageOwned {
     #[cfg(any(target_os = "android", target_os = "fuchsia", target_os = "linux"))]
     RxqOvfl(u32),
 
+    /// Socket error queue control messages read with the `MSG_ERRQUEUE` flag.
+    #[cfg(any(target_os = "android", target_os = "linux"))]
+    Ipv4RecvErr(libc::sock_extended_err, Option<sockaddr_in>),
+    /// Socket error queue control messages read with the `MSG_ERRQUEUE` flag.
+    #[cfg(any(target_os = "android", target_os = "linux"))]
+    Ipv6RecvErr(libc::sock_extended_err, Option<sockaddr_in6>),
+
     /// Catch-all variant for unimplemented cmsg types.
     #[doc(hidden)]
     Unknown(UnknownCmsg),
@@ -756,6 +763,16 @@ impl ControlMessageOwned {
                 let drop_counter = ptr::read_unaligned(p as *const u32);
                 ControlMessageOwned::RxqOvfl(drop_counter)
             },
+            #[cfg(any(target_os = "android", target_os = "linux"))]
+            (libc::IPPROTO_IP, libc::IP_RECVERR) => {
+                let (err, addr) = Self::recv_err_helper::<sockaddr_in>(p, len);
+                ControlMessageOwned::Ipv4RecvErr(err, addr)
+            },
+            #[cfg(any(target_os = "android", target_os = "linux"))]
+            (libc::IPPROTO_IPV6, libc::IPV6_RECVERR) => {
+                let (err, addr) = Self::recv_err_helper::<sockaddr_in6>(p, len);
+                ControlMessageOwned::Ipv6RecvErr(err, addr)
+            },
             (_, _) => {
                 let sl = slice::from_raw_parts(p, len);
                 let ucmsg = UnknownCmsg(*header, Vec::<u8>::from(sl));
@@ -763,6 +780,24 @@ impl ControlMessageOwned {
             }
         }
     }
+
+    #[cfg(any(target_os = "android", target_os = "linux"))]
+    unsafe fn recv_err_helper<T>(p: *mut libc::c_uchar, len: usize) -> (libc::sock_extended_err, Option<T>) {
+        let ee = p as *const libc::sock_extended_err;
+        let err = ptr::read_unaligned(ee);
+
+        // For errors originating on the network, SO_EE_OFFENDER(ee) points inside the p[..len]
+        // CMSG_DATA buffer.  For local errors, there is no address included in the control
+        // message, and SO_EE_OFFENDER(ee) points beyond the end of the buffer.  So, we need to
+        // validate that the address object is in-bounds before we attempt to copy it.
+        let addrp = libc::SO_EE_OFFENDER(ee) as *const T;
+
+        if addrp.offset(1) as usize - (p as usize) > len {
+            (err, None)
+        } else {
+            (err, Some(ptr::read_unaligned(addrp)))
+        }
+    }
 }
 
 /// A type-safe zero-copy wrapper around a single control message, as used wih
diff --git a/src/sys/socket/sockopt.rs b/src/sys/socket/sockopt.rs
index a937226f..195479b6 100644
--- a/src/sys/socket/sockopt.rs
+++ b/src/sys/socket/sockopt.rs
@@ -345,6 +345,10 @@ sockopt_impl!(Both, UdpGroSegment, libc::IPPROTO_UDP, libc::UDP_GRO, bool);
 #[cfg(any(target_os = "android", target_os = "fuchsia", target_os = "linux"))]
 sockopt_impl!(Both, RxqOvfl, libc::SOL_SOCKET, libc::SO_RXQ_OVFL, libc::c_int);
 sockopt_impl!(Both, Ipv6V6Only, libc::IPPROTO_IPV6, libc::IPV6_V6ONLY, bool);
+#[cfg(any(target_os = "android", target_os = "linux"))]
+sockopt_impl!(Both, Ipv4RecvErr, libc::IPPROTO_IP, libc::IP_RECVERR, bool);
+#[cfg(any(target_os = "android", target_os = "linux"))]
+sockopt_impl!(Both, Ipv6RecvErr, libc::IPPROTO_IPV6, libc::IPV6_RECVERR, bool);
 
 #[cfg(any(target_os = "android", target_os = "linux"))]
 #[derive(Copy, Clone, Debug)]