commit b50dd3bc8cbb1efe85399b03d7e6c0310c2ead84
Author: Florian Weimer <fw@deneb.enyo.de>
Date:   Mon Dec 31 22:04:36 2018 +0100

    malloc: Always call memcpy in _int_realloc [BZ #24027]
    
    This commit removes the custom memcpy implementation from _int_realloc
    for small chunk sizes.  The ncopies variable has the wrong type, and
    an integer wraparound could cause the existing code to copy too few
    elements (leaving the new memory region mostly uninitialized).
    Therefore, removing this code fixes bug 24027.

diff -rup a/malloc/malloc.c b/malloc/malloc.c
--- a/malloc/malloc.c	2019-03-26 14:12:59.364333388 -0400
+++ b/malloc/malloc.c	2019-03-26 14:17:17.373475418 -0400
@@ -4214,11 +4214,6 @@ _int_realloc(mstate av, mchunkptr oldp,
   mchunkptr        bck;             /* misc temp for linking */
   mchunkptr        fwd;             /* misc temp for linking */
 
-  unsigned long    copysize;        /* bytes to copy */
-  unsigned int     ncopies;         /* INTERNAL_SIZE_T words to copy */
-  INTERNAL_SIZE_T* s;               /* copy source */
-  INTERNAL_SIZE_T* d;               /* copy destination */
-
   const char *errstr = NULL;
 
   /* oldmem size */
@@ -4291,39 +4286,7 @@ _int_realloc(mstate av, mchunkptr oldp,
 	newp = oldp;
       }
       else {
-	/*
-	  Unroll copy of <= 36 bytes (72 if 8byte sizes)
-	  We know that contents have an odd number of
-	  INTERNAL_SIZE_T-sized words; minimally 3.
-	*/
-
-	copysize = oldsize - SIZE_SZ;
-	s = (INTERNAL_SIZE_T*)(chunk2mem(oldp));
-	d = (INTERNAL_SIZE_T*)(newmem);
-	ncopies = copysize / sizeof(INTERNAL_SIZE_T);
-	assert(ncopies >= 3);
-
-	if (ncopies > 9)
-	  MALLOC_COPY(d, s, copysize);
-
-	else {
-	  *(d+0) = *(s+0);
-	  *(d+1) = *(s+1);
-	  *(d+2) = *(s+2);
-	  if (ncopies > 4) {
-	    *(d+3) = *(s+3);
-	    *(d+4) = *(s+4);
-	    if (ncopies > 6) {
-	      *(d+5) = *(s+5);
-	      *(d+6) = *(s+6);
-	      if (ncopies > 8) {
-		*(d+7) = *(s+7);
-		*(d+8) = *(s+8);
-	      }
-	    }
-	  }
-	}
-
+	memcpy (newmem, chunk2mem (oldp), oldsize - SIZE_SZ);
 	_int_free(av, oldp, 1);
 	check_inuse_chunk(av, newp);
 	return chunk2mem(newp);