Clean environment variables to account for sandbox work directory.

Unset HOME to prevent username leak.

Bug: 363037195

Change-Id: I7a8694f746d58de8f6e41adb6ad52abbaf955ef4

ui/build/sandbox_linux.go

@@ -187,8 +187,17 @@ func (c *Cmd) readMountArgs() []string {
 	return args
 }
 
+func (c *Cmd) workDir() string {
+	if !c.config.UseABFS() {
+		wd, _ := os.Getwd()
+		return wd
+	}
+
+	return abfsSrcDir
+}
+
 func (c *Cmd) wrapSandbox() {
-	wd, _ := os.Getwd()
+	wd := c.workDir()
 
 	var sandboxArgs []string
 	sandboxArgs = append(sandboxArgs,
@@ -226,7 +235,7 @@ func (c *Cmd) wrapSandbox() {
 	)
 
 	sandboxArgs = append(sandboxArgs,
-		c.readMountArgs()...
+		c.readMountArgs()...,
 	)
 
 	sandboxArgs = append(sandboxArgs,