tpm: Add recv timeout while running recvmsg

If swtpm becomes unresponsive, guest gets blocked at "recvmsg" on tpm's
data FD. This change adds a timeout to the data fd socket. If swtpm
becomes unresponsive guest waits for "timeout" (secs) and continues to
run after returning an I/O error to tpm commands.

Signed-off-by: Praveen K Paladugu <prapal@linux.microsoft.com>

tpm/src/emulator.rs

@@ -143,6 +143,27 @@ impl Emulator {
         self.run_control_cmd(Commands::CmdSetDatafd, &mut res, 0, mem::size_of::<u32>())?;
         debug!("data fd in cloud-hypervisor = {:?}", fds[0]);
         self.data_fd = fds[0];
+
+        // SAFETY: FFI calls and return value of the unsafe call is checked
+        unsafe {
+            let tv = net_gen::iff::timeval {
+                tv_sec: 0,
+                tv_usec: 100000, // Set recv timeout to 100ms
+            };
+            let ret = net_gen::setsockopt(
+                fds[0],
+                net_gen::iff::SOL_SOCKET as i32,
+                net_gen::iff::SO_RCVTIMEO as i32,
+                &tv as *const _ as *const libc::c_void,
+                std::mem::size_of::<net_gen::iff::timeval>() as u32,
+            );
+            if ret == -1 {
+                return Err(Error::PrepareDataFd(anyhow!(
+                    "Failed to set receive timeout on data fd socket. Error Code {:?}",
+                    std::io::Error::last_os_error()
+                )));
+            }
+        }
         self.control_socket.set_datafd(fds[0]);
         Ok(())
     }