From c5498642fc4116241bc7f325f5f8830ea182cca8 Mon Sep 17 00:00:00 2001
From: Russ Magee <rmagee@gmail.com>
Date: Fri, 4 May 2018 23:25:26 -0700
Subject: [PATCH] Got client hangup working again. Security scrub auth vars.

---
 hkexauth.go        | 11 ++++++++---
 hkexnet.go         | 21 +++++++++------------
 hkexsh/hkexsh.go   | 14 +++++++++-----
 hkexshd/hkexshd.go |  7 +++++++
 4 files changed, 33 insertions(+), 20 deletions(-)

diff --git a/hkexauth.go b/hkexauth.go
index 84c15d6..5d6aa0a 100644
--- a/hkexauth.go
+++ b/hkexauth.go
@@ -28,9 +28,6 @@ func AuthUser(username string, auth string, fname string) (valid bool, allowedCm
 	}
 	r := csv.NewReader(bytes.NewReader(b))
 
-	b = nil
-	runtime.GC() // Paranoia and prob. not effective; kill authFile in b[]
-
 	r.Comma = ':'
 	r.Comment = '#'
 	r.FieldsPerRecord = 4 // username:salt:authCookie:disallowedCmdList (a,b,...)
@@ -51,5 +48,13 @@ func AuthUser(username string, auth string, fname string) (valid bool, allowedCm
 			break
 		}
 	}
+	// Security scrub
+	for i := range b {
+		b[i] = 0
+	}
+	b = nil
+	r = nil
+	runtime.GC()
+
 	return
 }
diff --git a/hkexnet.go b/hkexnet.go
index e1c63e7..05ce922 100644
--- a/hkexnet.go
+++ b/hkexnet.go
@@ -319,8 +319,6 @@ func (hl HKExListener) Accept() (hc Conn, err error) {
 // See go doc io.Reader
 func (c Conn) Read(b []byte) (n int, err error) {
 	//log.Printf("[Decrypting...]\r\n")
-	log.Printf("Read() requests %d bytes\n", len(b))
-
 	for {
 		//log.Printf("c.dBuf.Len(): %d\n", c.dBuf.Len())
 		if c.dBuf.Len() > 0 /* len(b) */ {
@@ -349,7 +347,6 @@ func (c Conn) Read(b []byte) (n int, err error) {
 				log.Println("unexpected Read() err:", err)
 			} else {
 				log.Println("[Client hung up]")
-				// TODO: Stop chaff if active
 			}
 			return 0, err
 		}
@@ -536,15 +533,15 @@ func (c *Conn) chaffHelper(szMax int) {
 
 // hkexsh.Copy() is a modified version of io.Copy()
 func Copy(dst io.Writer, src io.Reader) (written int64, err error) {
-	//	// If the reader has a WriteTo method, use it to do the copy.
-	//	// Avoids an allocation and a copy.
-	//	if wt, ok := src.(io.WriterTo); ok {
-	//		return wt.WriteTo(dst)
-	//	}
-	//	// Similarly, if the writer has a ReadFrom method, use it to do the copy.
-	//	if rt, ok := dst.(io.ReaderFrom); ok {
-	//		return rt.ReadFrom(src)
-	//	}
+	// If the reader has a WriteTo method, use it to do the copy.
+	// Avoids an allocation and a copy.
+	if wt, ok := src.(io.WriterTo); ok {
+		return wt.WriteTo(dst)
+	}
+	// Similarly, if the writer has a ReadFrom method, use it to do the copy.
+	if rt, ok := dst.(io.ReaderFrom); ok {
+		return rt.ReadFrom(src)
+	}
 
 	buf := make([]byte, 32*1024)
 	for {
diff --git a/hkexsh/hkexsh.go b/hkexsh/hkexsh.go
index d37535a..76a96c7 100644
--- a/hkexsh/hkexsh.go
+++ b/hkexsh/hkexsh.go
@@ -17,6 +17,7 @@ import (
 	"os/exec"
 	"os/signal"
 	"os/user"
+	"runtime"
 	"strings"
 	"sync"
 	"syscall"
@@ -79,7 +80,7 @@ func main() {
 	flag.StringVar(&server, "s", "localhost:2000", "server hostname/address[:port]")
 	flag.StringVar(&cmdStr, "x", "", "command to run (default empty - interactive shell)")
 	flag.StringVar(&altUser, "u", "", "specify alternate user")
-	flag.StringVar(&authCookie, "a", "", "auth cookie (MultiCheese3999(tm) 2FA cookie")
+	flag.StringVar(&authCookie, "a", "", "auth cookie")
 	flag.BoolVar(&dbg, "d", false, "debug logging")
 	flag.Parse()
 
@@ -145,6 +146,9 @@ func main() {
 			panic(err)
 		}
 		authCookie = string(ab)
+		// Security scrub
+		ab = nil
+		runtime.GC()
 	}
 
 	rec := &cmdSpec{
@@ -187,8 +191,10 @@ func main() {
 		}
 
 		if isInteractive {
-			log.Println("[Got EOF]")
-			wg.Done() // server hung up, close WaitGroup to exit client
+			log.Println("[* Got EOF *]")
+			_ = hkexsh.Restore(int(os.Stdin.Fd()), oldState) // Best effort.
+			wg.Done()
+			os.Exit(0)
 		}
 	}()
 
@@ -236,8 +242,6 @@ func main() {
 				}
 			}
 			log.Println("[Sent EOF]")
-			//FIXME: regression circa. April 30 2018 on 'exit' from client,
-			//fixme: Enter/RETURN required prior to actua client exit
 			wg.Done() // client hung up, close WaitGroup to exit client
 		}()
 	}
diff --git a/hkexshd/hkexshd.go b/hkexshd/hkexshd.go
index a207847..e33180f 100644
--- a/hkexshd/hkexshd.go
+++ b/hkexshd/hkexshd.go
@@ -16,6 +16,7 @@ import (
 	"os"
 	"os/exec"
 	"os/user"
+	"runtime"
 	"syscall"
 
 	hkexsh "blitter.com/go/hkexsh"
@@ -246,6 +247,12 @@ func main() {
 					rec.op[0], string(rec.who), string(rec.cmd))
 
 				valid, allowedCmds := hkexsh.AuthUser(string(rec.who), string(rec.authCookie), "/etc/hkexsh.passwd")
+				// Security scrub
+				for i := range rec.authCookie {
+					rec.authCookie[i] = 0
+				}
+				runtime.GC()
+
 				if !valid {
 					log.Println("Invalid user", string(rec.who))
 					c.Write([]byte(rejectUserMsg()))