[PATCH] Cygwin: mmap: fix mapping beyond EOF on 64 bit
Ken Brown
kbrown@cornell.edu
Mon Jul 20 13:34:42 GMT 2020
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.
One consequence of this bug is that orig_len could be slightly smaller
than len. Since these are both unsigned values, the statement
'orig_len -= len' would 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.
---
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 ());
--
2.27.0
More information about the Cygwin-patches
mailing list