linux-kernel - [PATCH 84/91] x86: Fix mmap random address range

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Date:	Sun, 05 Feb 2012 23:11:13 +0100
From:	Willy Tarreau <w@....eu>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	Ludwig Nussel <ludwig.nussel@...e.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	harvey.harrison@...il.com, "H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Greg KH <gregkh@...uxfoundation.org>
Subject: [PATCH 84/91] x86: Fix mmap random address range

2.6.27-longterm review patch.  If anyone has any objections, please let us know.

------------------

commit 9af0c7a6fa860698d080481f24a342ba74b68982 upstream.

On x86_32 casting the unsigned int result of get_random_int() to
long may result in a negative value.  On x86_32 the range of
mmap_rnd() therefore was -255 to 255.  The 32bit mode on x86_64
used 0 to 255 as intended.

The bug was introduced by 675a081 ("x86: unify mmap_{32|64}.c")
in January 2008.

Signed-off-by: Ludwig Nussel <ludwig.nussel@...e.de>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: harvey.harrison@...il.com
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: Harvey Harrison <harvey.harrison@...il.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Link: http://lkml.kernel.org/r/201111152246.pAFMklOB028527@wpaz5.hot.corp.google.com
Signed-off-by: Ingo Molnar <mingo@...e.hu>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>
---
 arch/x86/mm/mmap.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

Index: longterm-2.6.27/arch/x86/mm/mmap.c
===================================================================
--- longterm-2.6.27.orig/arch/x86/mm/mmap.c	2012-02-05 22:34:32.437915058 +0100
+++ longterm-2.6.27/arch/x86/mm/mmap.c	2012-02-05 22:34:46.864914382 +0100
@@ -87,9 +87,9 @@
 	*/
 	if (current->flags & PF_RANDOMIZE) {
 		if (mmap_is_ia32())
-			rnd = (long)get_random_int() % (1<<8);
+			rnd = get_random_int() % (1<<8);
 		else
-			rnd = (long)(get_random_int() % (1<<28));
+			rnd = get_random_int() % (1<<28);
 	}
 	return rnd << PAGE_SHIFT;
 }


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