linux-kernel - [PATCH] fix mmap random address range on x86

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Date:	Fri, 18 Feb 2011 14:15:57 +0100
From:	Ludwig Nussel <ludwig.nussel@...e.de>
To:	linux-kernel@...r.kernel.org
Cc:	x86@...nel.org, Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, security@...nel.org,
	Ludwig Nussel <ludwig.nussel@...e.de>
Subject: [PATCH] fix mmap random address range on x86

On x86 casting the unsigned int result of get_random_int() to long
may result in a negative value. On x86 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 commit 675a081 in January 2008.

Signed-off-by: Ludwig Nussel <ludwig.nussel@...e.de>
---
 arch/x86/mm/mmap.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
index 1dab519..f927429 100644
--- 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;
 }
-- 
1.7.1

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