[glibc/release/2.28/master] malloc: Check the alignment of mmapped chunks before unmapping.

[Arjun Shankar <arjun at sourceware dot org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=38e89818335400b5593943f92a379b9c669b758c

commit 38e89818335400b5593943f92a379b9c669b758c
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.
    
    (cherry picked from commit c0e82f117357a941e4d40fcc08babbd6a3c3a1b5)

Diff:
---
 ChangeLog       | 4 ++++
 malloc/malloc.c | 5 ++++-
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/ChangeLog b/ChangeLog
index e2d7e3c..c9448ac 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+2018-12-21  Istvan Kurucsai <pistukem@gmail.com>
+
+	* malloc/malloc.c (munmap_chunk): Verify chunk alignment.
+
 2018-12-20  Istvan Kurucsai <pistukem@gmail.com>
 
 	* malloc/malloc.c (mremap_chunk): Additional checks.
diff --git a/malloc/malloc.c b/malloc/malloc.c
index 7880fcd..6ae22e6 100644
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -2810,6 +2810,7 @@ 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));
@@ -2819,6 +2820,7 @@ 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
@@ -2826,7 +2828,8 @@ 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);