[Emacs-diffs] emacs-25 ab849b7: Fix w32 memory-management problem when extending buffer text

[Eli Zaretskii]

branch: emacs-25
commit ab849b7fac5f7a4bb301eb830fa0acc3ad18c18f
Author: Eli Zaretskii <address@hidden>
Commit: Eli Zaretskii <address@hidden>

    Fix w32 memory-management problem when extending buffer text
    
    * src/w32heap.c (mmap_realloc): Only attempt extending a region if
    the following region has the same allocation base.  Also, use the
    original allocation base and enlarged size to commit reserved
    memory, to ensure that the allocation base stays at its original
    value.  This fixes several hard-to-debug problems whereby part of
    buffer text was overwritten with binary nulls, because
    mmap_realloc copied only part of buffer text when extending it.
    See
    http://lists.gnu.org/archive/html/emacs-devel/2016-04/msg00325.html
    and http://debbugs.gnu.org/cgi/bugreport.cgi?bug=23223#55 for two
    examples of the related problems.
---
 src/w32heap.c |    8 ++++----
 1 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/src/w32heap.c b/src/w32heap.c
index df2fe0a..6643b43 100644
--- a/src/w32heap.c
+++ b/src/w32heap.c
@@ -714,13 +714,12 @@ mmap_realloc (void **var, size_t nbytes)
       /* If there is enough room in the current reserved area, then
         commit more pages as needed.  */
       if (m2.State == MEM_RESERVE
+         && m2.AllocationBase == memInfo.AllocationBase
          && nbytes <= memInfo.RegionSize + m2.RegionSize)
        {
          void *p;
 
-         p = VirtualAlloc (*var + memInfo.RegionSize,
-                           nbytes - memInfo.RegionSize,
-                           MEM_COMMIT, PAGE_READWRITE);
+         p = VirtualAlloc (*var, nbytes, MEM_COMMIT, PAGE_READWRITE);
          if (!p /* && GetLastError() != ERROR_NOT_ENOUGH_MEMORY */)
            {
              DebPrint (("realloc enlarge: VirtualAlloc (%p + %I64x, %I64x) 
error %ld\n",
@@ -728,7 +727,8 @@ mmap_realloc (void **var, size_t nbytes)
                         (uint64_t)(nbytes - memInfo.RegionSize),
                         GetLastError ()));
              DebPrint (("next region: %p %p %I64x %x\n", m2.BaseAddress,
-                        m2.AllocationBase, m2.RegionSize, 
m2.AllocationProtect));
+                        m2.AllocationBase, (uint64_t)m2.RegionSize,
+                        m2.AllocationProtect));
            }
          else
            return *var;