Fix buffer overrun with unbuffered custom binary input ports.

Fixes <http://bugs.gnu.org/19621>.

Before that, in 'cbip_fill_input', BUFFERED would be set to 0 when
reading from 'scm_getc' et al, because 'shortbuf' was being used.  Thus,
we could eventually execute this line:

      /* Copy the data back to the internal buffer.  */
      memcpy ((char *) c_port->read_pos, SCM_BYTEVECTOR_CONTENTS (bv),
	      c_octets);

But 'read_pos' would quickly point to the fields beyond 'shortbuf',
thereby leading to a corruption of the 'scm_t_port' itself.

* libguile/r6rs-ports.c (cbip_setvbuf): When READ_SIZE is 0, keep using
  BV as the 'read_buf'.
  (cbip_fill_input): Adjust assertion to accept 'read_buf_size = 1'.
* test-suite/tests/r6rs-ports.test ("7.2.7 Input Ports")["custom binary
  input port unbuffered & 'get-string-all'", "custom binary input port
  unbuffered UTF-8 & 'get-string-all'"]: New tests.

libguile/r6rs-ports.c

@@ -1,4 +1,4 @@
-/* Copyright (C) 2009, 2010, 2011, 2013, 2014 Free Software Foundation, Inc.
+/* Copyright (C) 2009, 2010, 2011, 2013-2015 Free Software Foundation, Inc.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public License
@@ -307,9 +307,10 @@ cbip_setvbuf (SCM port, long read_size, long write_size)
   switch (read_size)
     {
     case 0:
-      /* Unbuffered: keep PORT's bytevector as is (it will be used in
+      /* Unbuffered: keep using PORT's bytevector as the underlying
-	 future 'scm_c_read' calls), but point to the one-byte buffer.  */
+	 buffer (it will also be used by future 'scm_c_read' calls.)  */
-      pt->read_buf = &pt->shortbuf;
+      assert (SCM_BYTEVECTOR_LENGTH (bv) >= 1);
+      pt->read_buf = (unsigned char *) SCM_BYTEVECTOR_CONTENTS (bv);
       pt->read_buf_size = 1;
       break;
 
@@ -404,9 +405,11 @@ cbip_fill_input (SCM port)
 
       if (buffered)
 	{
-	  /* Make sure the buffer isn't corrupt.  BV can be passed directly
+	  /* Make sure the buffer isn't corrupt.  Its size can be 1 when
-	     to READ_PROC.  */
+	     someone called 'setvbuf' with _IONBF.  BV can be passed
-	  assert (c_port->read_buf_size == SCM_BYTEVECTOR_LENGTH (bv));
+	     directly to READ_PROC.  */
+	  assert (c_port->read_buf_size == SCM_BYTEVECTOR_LENGTH (bv)
+		  || c_port->read_buf_size == 1);
 	  c_port->read_pos = (unsigned char *) SCM_BYTEVECTOR_CONTENTS (bv);
 	}
       else

test-suite/tests/r6rs-ports.test

@@ -1,6 +1,6 @@
 ;;;; r6rs-ports.test --- R6RS I/O port tests.   -*- coding: utf-8; -*-
 ;;;;
-;;;; Copyright (C) 2009, 2010, 2011, 2012, 2014 Free Software Foundation, Inc.
+;;;; Copyright (C) 2009-2012, 2014-2015 Free Software Foundation, Inc.
 ;;;; Ludovic Courtès
 ;;;;
 ;;;; This library is free software; you can redistribute it and/or
@@ -557,6 +557,37 @@ not `set-port-position!'"
                         obj))
                   ret)))))
 
+  (pass-if-equal "custom binary input port unbuffered & 'get-string-all'"
+      (make-string 1000 #\a)
+    ;; In Guile 2.0.11 this test would lead to a buffer overrun followed
+    ;; by an assertion failure.  See <http://bugs.gnu.org/19621>.
+    (let* ((input (with-fluids ((%default-port-encoding #f))
+                    (open-input-string (make-string 1000 #\a))))
+           (read! (lambda (bv index count)
+                    (let ((n (get-bytevector-n! input bv index
+                                                count)))
+                      (if (eof-object? n) 0 n))))
+           (port  (make-custom-binary-input-port "foo" read!
+                                                 #f #f #f)))
+      (setvbuf port _IONBF)
+      (get-string-all port)))
+
+  (pass-if-equal "custom binary input port unbuffered UTF-8 & 'get-string-all'"
+      (make-string 1000 #\λ)
+    ;; In Guile 2.0.11 this test would lead to a buffer overrun followed
+    ;; by an assertion failure.  See <http://bugs.gnu.org/19621>.
+    (let* ((input (with-fluids ((%default-port-encoding "UTF-8"))
+                    (open-input-string (make-string 1000 #\λ))))
+           (read! (lambda (bv index count)
+                    (let ((n (get-bytevector-n! input bv index
+                                                count)))
+                      (if (eof-object? n) 0 n))))
+           (port  (make-custom-binary-input-port "foo" read!
+                                                 #f #f #f)))
+      (setvbuf port _IONBF)
+      (set-port-encoding! port "UTF-8")
+      (get-string-all port)))
+
   (pass-if-equal "custom binary input port, unbuffered then buffered"
       `((6 "Lorem ") (12 "ipsum dolor ") (777 "sit amet, consectetur…")
         (777 ,(eof-object)))