[RFC][PATCH 7/7] malloc: Check the alignment of mmapped chunks before unmapping.

[Istvan Kurucsai <pistukem at gmail dot com>]

    * malloc/malloc.c (munmap_chunk): Verify chunk alignment.
---
 malloc/malloc.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/malloc/malloc.c b/malloc/malloc.c
index 503d061..f84e51a 100644
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -2799,6 +2799,7 @@ static void
 internal_function
 munmap_chunk (mchunkptr p)
 {
+  size_t pagesize = GLRO (dl_pagesize);
   INTERNAL_SIZE_T size = chunksize (p);
 
   assert (chunk_is_mmapped (p));
@@ -2809,13 +2810,15 @@ munmap_chunk (mchunkptr p)
     return;
 
   uintptr_t block = (uintptr_t) p - prev_size (p);
+  uintptr_t mem = (uintptr_t) chunk2mem(p);
   size_t total_size = prev_size (p) + size;
   /* Unfortunately we have to do the compilers job by hand here.  Normally
      we would test BLOCK and TOTAL-SIZE separately for compliance with the
      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 (check_action, "munmap_chunk(): invalid pointer",
                        chunk2mem (p), NULL);
-- 
2.7.4