commit c0e82f117357a941e4d40fcc08babbd6a3c3a1b5
Author: Istvan Kurucsai <pistukem@gmail.com>
Date:   Fri Dec 21 00:13:01 2018 -0500

    malloc: Check the alignment of mmapped chunks before unmapping.
    
    * malloc/malloc.c (munmap_chunk): Verify chunk alignment.

diff --git a/malloc/malloc.c b/malloc/malloc.c
index 4df5cb4862a7b854..4412a4ffc83b013b 100644
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -2817,6 +2817,7 @@ systrim (size_t pad, mstate av)
 static void
 munmap_chunk (mchunkptr p)
 {
+  size_t pagesize = GLRO (dl_pagesize);
   INTERNAL_SIZE_T size = chunksize (p);
 
   assert (chunk_is_mmapped (p));
@@ -2826,6 +2827,7 @@ munmap_chunk (mchunkptr p)
   if (DUMPED_MAIN_ARENA_CHUNK (p))
     return;
 
+  uintptr_t mem = (uintptr_t) chunk2mem (p);
   uintptr_t block = (uintptr_t) p - prev_size (p);
   size_t total_size = prev_size (p) + size;
   /* Unfortunately we have to do the compilers job by hand here.  Normally
@@ -2833,7 +2835,8 @@ munmap_chunk (mchunkptr p)
      page size.  But gcc does not recognize the optimization possibility
      (in the moment at least) so we combine the two values into one before
      the bit test.  */
-  if (__builtin_expect (((block | total_size) & (GLRO (dl_pagesize) - 1)) != 0, 0))
+  if (__glibc_unlikely ((block | total_size) & (pagesize - 1)) != 0
+      || __glibc_unlikely (!powerof2 (mem & (pagesize - 1))))
     malloc_printerr ("munmap_chunk(): invalid pointer");
 
   atomic_decrement (&mp_.n_mmaps);