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 --git a/malloc/malloc.c b/malloc/malloc.c
index 7bfa66a56786d110..0234d968c0ce65a0 100644
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -4532,11 +4532,6 @@ _int_realloc(mstate av, mchunkptr oldp, INTERNAL_SIZE_T oldsize,
   mchunkptr        remainder;       /* extra space at end of newp */
   unsigned long    remainder_size;  /* its size */
 
-  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 */
-
   /* oldmem size */
   if (__builtin_expect (chunksize_nomask (oldp) <= 2 * SIZE_SZ, 0)
       || __builtin_expect (oldsize >= av->system_mem, 0))
@@ -4604,43 +4599,7 @@ _int_realloc(mstate av, mchunkptr oldp, INTERNAL_SIZE_T oldsize,
             }
           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)
-                memcpy (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);