[PATCH] sysmalloc: Initialize previous size field of mmaped chunks

[Florian Weimer]

With different encodings of the header, the previous zero initialization
may be insufficient and produce an invalid encoding.

2016-10-27  Florian Weimer  <fweimer@redhat.com>

	* malloc/malloc.c (sysmalloc): Initialize previous size field of
	mmaped chunks.

diff --git a/malloc/malloc.c b/malloc/malloc.c
index 186e174..72d22bd 100644
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -2306,6 +2306,7 @@ sysmalloc (INTERNAL_SIZE_T nb, mstate av)
               else
                 {
                   p = (mchunkptr) mm;
+		  set_prev_size (p, 0);
                   set_head (p, size | IS_MMAPPED);
                 }