[12/27] x86: Fix mmap random address range

[Greg KH]

2.6.32-longterm review patch.  If anyone has any objections, please let me know.

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

From: Ludwig Nussel <ludwig.nussel@xxxxxxx>

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@xxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: harvey.harrison@xxxxxxxxx
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Harvey Harrison <harvey.harrison@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/201111152246.pAFMklOB028527@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 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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