linux-kernel - [48/48] x86: Fix mmap random address range

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Message-Id: <20120116184519.755069782@clark.kroah.org>
Date:	Mon, 16 Jan 2012 10:45:15 -0800
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Ludwig Nussel <ludwig.nussel@...e.de>,
	harvey.harrison@...il.com, "H. Peter Anvin" <hpa@...or.com>,
	Ingo Molnar <mingo@...e.hu>
Subject: [48/48] x86: Fix mmap random address range

3.1-stable review patch.  If anyone has any objections, please let me know.

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

From: Ludwig Nussel <ludwig.nussel@...e.de>

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 file changed, 2 insertions(+), 2 deletions(-)

--- a/arch/x86/mm/mmap.c
+++ b/arch/x86/mm/mmap.c
@@ -87,9 +87,9 @@ static unsigned long mmap_rnd(void)
 	*/
 	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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