Fix integer overflow in malloc when tcache is enabled [BZ #22375]

When the per-thread cache is enabled, __libc_malloc uses request2size (which
does not perform an overflow check) to calculate the chunk size from the
requested allocation size. This leads to an integer overflow causing malloc
to incorrectly return the last successfully allocated block when called with
a very large size argument (close to SIZE_MAX).

This commit uses checked_request2size instead, removing the overflow.

ChangeLog

@@ -1,3 +1,9 @@
+2017-11-30  Arjun Shankar  <arjun@redhat.com>
+
+	[BZ #22375]
+	* malloc/malloc.c (__libc_malloc): Use checked_request2size
+	instead of request2size.
+
 2017-11-30  Joseph Myers  <joseph@codesourcery.com>
 
 	* sysdeps/sparc/sparc32/sparcv9/fpu/multiarch/s_llrint.S

malloc/malloc.c

@@ -3031,7 +3031,8 @@ __libc_malloc (size_t bytes)
     return (*hook)(bytes, RETURN_ADDRESS (0));
 #if USE_TCACHE
   /* int_free also calls request2size, be careful to not pad twice.  */
-  size_t tbytes = request2size (bytes);
+  size_t tbytes;
+  checked_request2size (bytes, tbytes);
   size_t tc_idx = csize2tidx (tbytes);
 
   MAYBE_INIT_TCACHE ();