[Top][All Lists]
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Bug-gnulib] linebreak.c proposed patches for size-calculation overf
From: |
Paul Eggert |
Subject: |
Re: [Bug-gnulib] linebreak.c proposed patches for size-calculation overflows |
Date: |
10 Nov 2003 15:59:04 -0800 |
User-agent: |
Gnus/5.09 (Gnus v5.9.0) Emacs/21.3 |
Bruno Haible <address@hidden> writes:
> > +# define xalloc_oversized(n, s) ((size_t) -1 / (s) <= (n))
> I think this expression is wrong, and should better be written as
> ((size_t) -2 / (s) < (n))
Good catch; thanks. I installed this patch.
2003-11-10 Paul Eggert <address@hidden>
* xalloc.h (xalloc_oversized): [! (defined PTRDIFF_MAX &&
PTRDIFF_MAX < SIZE_MAX)]: Fix off-by-one error that would have
rejected some allocations of exactly SIZE_MAX - 2 bytes.
From Bruno Haible.
[defined PTRDIFF_MAX && PTRDIFF_MAX < SIZE_MAX]: Use SIZE_MAX,
not (size_t) -1, since it's defined here.
--- xalloc.h.~1.21.~ Thu Nov 6 11:40:53 2003
+++ xalloc.h Mon Nov 10 15:51:31 2003
@@ -68,15 +68,16 @@ char *xstrdup (const char *str);
works correctly even when SIZE_MAX < N.
By gnulib convention, SIZE_MAX represents overflow in size
- calculations, so reject attempted allocations of exactly SIZE_MAX
- bytes. However, malloc (SIZE_MAX) fails on all known hosts where
+ calculations, so the conservative dividend to use here is
+ SIZE_MAX - 1, since SIZE_MAX might represent an overflowed value.
+ However, malloc (SIZE_MAX) fails on all known hosts where
PTRDIFF_MAX < SIZE_MAX, so do not bother to test for
exactly-SIZE_MAX allocations on such hosts; this avoids a test and
branch when S is known to be 1. */
# if defined PTRDIFF_MAX && PTRDIFF_MAX < SIZE_MAX
-# define xalloc_oversized(n, s) ((size_t) -1 / (s) < (n))
-# else
-# define xalloc_oversized(n, s) ((size_t) -1 / (s) <= (n))
+# define xalloc_oversized(n, s) (SIZE_MAX / (s) < (n))
+# else /* SIZE_MAX might not be defined, so avoid (SIZE_MAX - 1). */
+# define xalloc_oversized(n, s) ((size_t) -2 / (s) < (n))
# endif
/* These macros are deprecated; they will go away soon, and are retained
- Re: [Bug-gnulib] linebreak.c proposed patches for size-calculation overflows, Bruno Haible, 2003/11/03
- Re: [Bug-gnulib] linebreak.c proposed patches for size-calculation overflows, Paul Eggert, 2003/11/03
- Re: [Bug-gnulib] linebreak.c proposed patches for size-calculation overflows, Bruno Haible, 2003/11/04
- Re: [Bug-gnulib] linebreak.c proposed patches for size-calculation overflows, Paul Eggert, 2003/11/04
- Re: [Bug-gnulib] linebreak.c proposed patches for size-calculation overflows, Bruno Haible, 2003/11/05
- Re: [Bug-gnulib] linebreak.c proposed patches for size-calculation overflows, Paul Eggert, 2003/11/05
- Re: [Bug-gnulib] linebreak.c proposed patches for size-calculation overflows, Bruno Haible, 2003/11/06
- Re: [Bug-gnulib] linebreak.c proposed patches for size-calculation overflows, Paul Eggert, 2003/11/06
- Re: [Bug-gnulib] linebreak.c proposed patches for size-calculation overflows, Bruno Haible, 2003/11/10
- Re: [Bug-gnulib] linebreak.c proposed patches for size-calculation overflows,
Paul Eggert <=
- [Bug-gnulib] Re: linebreak.c proposed patches for size-calculation overflows, Simon Josefsson, 2003/11/19
- [Bug-gnulib] Re: linebreak.c proposed patches for size-calculation overflows, Paul Eggert, 2003/11/19
- Re: [Bug-gnulib] Re: linebreak.c proposed patches for size-calculation overflows, Bruno Haible, 2003/11/19
- Re: [Bug-gnulib] Re: linebreak.c proposed patches for size-calculation overflows, Paul Eggert, 2003/11/19
- [Bug-gnulib] Re: linebreak.c proposed patches for size-calculation overflows, Simon Josefsson, 2003/11/19
- [Bug-gnulib] Re: linebreak.c proposed patches for size-calculation overflows, Simon Josefsson, 2003/11/19
- Re: [Bug-gnulib] Re: linebreak.c proposed patches for size-calculation overflows, James Youngman, 2003/11/19
- Re: [Bug-gnulib] Re: linebreak.c proposed patches for size-calculation overflows, Paul Eggert, 2003/11/19
- [Bug-gnulib] Re: linebreak.c proposed patches for size-calculation overflows, Paul Eggert, 2003/11/19
- Re: [Bug-gnulib] Re: linebreak.c proposed patches for size-calculation overflows, Bruno Haible, 2003/11/19