[PATCH] xalloc: x2nrealloc check for ptrdiff_t overflow

[Paul Eggert]

* lib/xalloc.h (x2nrealloc): Check for ptrdiff_t overflow, too.
* modules/xalloc, modules/xvasprintf (Depends-on): Add stdint.
---
 ChangeLog          |  6 ++++++
 lib/xalloc.h       | 10 ++++++----
 modules/xalloc     |  1 +
 modules/xvasprintf |  1 +
 4 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index b1f41bb..92dda3a 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2016-12-29  Paul Eggert  <egg...@cs.ucla.edu>
+
+       xalloc: x2nrealloc check for ptrdiff_t overflow
+       * lib/xalloc.h (x2nrealloc): Check for ptrdiff_t overflow, too.
+       * modules/xalloc, modules/xvasprintf (Depends-on): Add stdint.
+
 2016-12-24  Bruno Haible  <br...@clisp.org>
 
        lock test: Fix performance problem on multi-core machines.
diff --git a/lib/xalloc.h b/lib/xalloc.h
index a4fddbf..3aad4e3 100644
--- a/lib/xalloc.h
+++ b/lib/xalloc.h
@@ -19,6 +19,7 @@
 #define XALLOC_H_
 
 #include <stddef.h>
+#include <stdint.h>
 
 #include "xalloc-oversized.h"
 
@@ -197,10 +198,11 @@ x2nrealloc (void *p, size_t *pn, size_t s)
   else
     {
       /* Set N = floor (1.5 * N) + 1 so that progress is made even if N == 0.
-         Check for overflow, so that N * S stays in size_t range.
-         The check may be slightly conservative, but an exact check isn't
-         worth the trouble.  */
-      if ((size_t) -1 / 3 * 2 / s <= n)
+         Check for overflow, so that N * S stays in both ptrdiff_t and
+         size_t range.  The check may be slightly conservative, but an
+         exact check isn't worth the trouble.  */
+      if ((PTRDIFF_MAX < SIZE_MAX ? PTRDIFF_MAX : SIZE_MAX) / 3 * 2 / s
+          <= n)
         xalloc_die ();
       n += n / 2 + 1;
     }
diff --git a/modules/xalloc b/modules/xalloc
index c6c2083..b107da9 100644
--- a/modules/xalloc
+++ b/modules/xalloc
@@ -8,6 +8,7 @@ m4/xalloc.m4
 
 Depends-on:
 extern-inline
+stdint
 xalloc-die
 xalloc-oversized
 
diff --git a/modules/xvasprintf b/modules/xvasprintf
index a931d7c..410b45f 100644
--- a/modules/xvasprintf
+++ b/modules/xvasprintf
@@ -17,6 +17,7 @@ vasprintf
 xalloc-die
 xsize
 stdarg
+stdint
 errno
 
 configure.ac:
-- 
2.7.4