Fix UB in the SO_TYPE sockopt

When reading a value into an enum from getsockopt, we must validate it.
Failing to do so can lead to UB for example with SOCK_PACKET on Linux.

Perform the validation in GetSockOpt::get.  Currently SockType is the
only type that requires validation.

Fixes #1819

2 files changed, 29 insertions, 4 deletions

diff --git a/src/sys/socket/mod.rs b/src/sys/socket/mod.rs
index a0702585..2d7159a6 100644
--- a/src/sys/socket/mod.rs
+++ b/src/sys/socket/mod.rs
@@ -12,7 +12,7 @@ use libc::{
     self, c_int, c_void, iovec, size_t, socklen_t, CMSG_DATA, CMSG_FIRSTHDR,
     CMSG_LEN, CMSG_NXTHDR,
 };
-use std::convert::TryInto;
+use std::convert::{TryFrom, TryInto};
 use std::io::{IoSlice, IoSliceMut};
 #[cfg(feature = "net")]
 use std::net;
@@ -107,6 +107,24 @@ pub enum SockType {
     #[cfg(not(any(target_os = "haiku")))]
     Rdm = libc::SOCK_RDM,
 }
+// The TryFrom impl could've been derived using libc_enum!.  But for
+// backwards-compatibility with Nix-0.25.0 we manually implement it, so as to
+// keep the old variant names.
+impl TryFrom<i32> for SockType {
+    type Error = crate::Error;
+
+    fn try_from(x: i32) -> Result<Self> {
+        match x {
+            libc::SOCK_STREAM => Ok(Self::Stream),
+            libc::SOCK_DGRAM => Ok(Self::Datagram),
+            libc::SOCK_SEQPACKET => Ok(Self::SeqPacket),
+            libc::SOCK_RAW => Ok(Self::Raw),
+            #[cfg(not(any(target_os = "haiku")))]
+            libc::SOCK_RDM => Ok(Self::Rdm),
+            _ => Err(Errno::EINVAL)
+        }
+    }
+}
 
 /// Constants used in [`socket`](fn.socket.html) and [`socketpair`](fn.socketpair.html)
 /// to specify the protocol to use.
diff --git a/src/sys/socket/sockopt.rs b/src/sys/socket/sockopt.rs
index 7489858e..06e9ee45 100644
--- a/src/sys/socket/sockopt.rs
+++ b/src/sys/socket/sockopt.rs
@@ -6,7 +6,10 @@ use crate::Result;
 use cfg_if::cfg_if;
 use libc::{self, c_int, c_void, socklen_t};
 use std::ffi::{OsStr, OsString};
-use std::mem::{self, MaybeUninit};
+use std::{
+    convert::TryFrom,
+    mem::{self, MaybeUninit}
+};
 #[cfg(target_family = "unix")]
 use std::os::unix::ffi::OsStrExt;
 use std::os::unix::io::RawFd;
@@ -102,7 +105,10 @@ macro_rules! getsockopt_impl {
                     );
                     Errno::result(res)?;
 
-                    Ok(getter.assume_init())
+                    match <$ty>::try_from(getter.assume_init()) {
+                        Err(_) => Err(Errno::EINVAL),
+                        Ok(r) => Ok(r)
+                    }
                 }
             }
         }
@@ -629,7 +635,8 @@ sockopt_impl!(
     GetOnly,
     libc::SOL_SOCKET,
     libc::SO_TYPE,
-    super::SockType
+    super::SockType,
+    GetStruct<i32>
 );
 sockopt_impl!(
     /// Returns a value indicating whether or not this socket has been marked to