[newlib-cygwin] Cygwin: mmap: fix mapping beyond EOF on 64 bit

[Ken Brown]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=d8a8d2ce5953af3383aff019596bdf7f7aef6c41

commit d8a8d2ce5953af3383aff019596bdf7f7aef6c41
Author: Ken Brown <kbrown@cornell.edu>
Date:   Mon Jul 20 08:59:09 2020 -0400

    Cygwin: mmap: fix mapping beyond EOF on 64 bit
    
    Commit 605bdcd410384dda6db66b9b8cd19e863702e1bb enabled mapping beyond
    EOF in 64 bit environments.  But the variable 'orig_len' did not get
    rounded up to a multiple of 64K.  This rounding was done on 32 bit
    only.  Fix this by rounding up orig_len on 64 bit, in the same place
    where 'len' is rounded up.
    
    Rounding up is needed to make sigbus_page_len a multiple of the
    allocation granularity.
    
    In addition, failing to round up could cause orig_len to be smaller
    than len.  Since these are both unsigned values, the statement
    'orig_len -= len' could then cause orig_len to be huge, and mmap would
    fail with errno EFBIG.
    
    I observed this failure while debugging the problem reported in
    
      https://sourceware.org/pipermail/cygwin/2020-July/245557.html.
    
    The failure can be seen by running the test case in that report under
    gdb or strace.

Diff:
---
 winsup/cygwin/mmap.cc | 1 +
 1 file changed, 1 insertion(+)

diff --git a/winsup/cygwin/mmap.cc b/winsup/cygwin/mmap.cc
index feb9e5d0e..a08d00f83 100644
--- a/winsup/cygwin/mmap.cc
+++ b/winsup/cygwin/mmap.cc
@@ -1144,6 +1144,7 @@ go_ahead:
 	 ends in, but there's nothing at all we can do about that. */
 #ifdef __x86_64__
       len = roundup2 (len, wincap.allocation_granularity ());
+      orig_len = roundup2 (orig_len, wincap.allocation_granularity ());
 #else
       len = roundup2 (len, wincap.is_wow64 () ? wincap.allocation_granularity ()
 					      : wincap.page_size ());