x86: Fix mmap random address range

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@suse.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: harvey.harrison@gmail.com
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/201111152246.pAFMklOB028527@wpaz5.hot.corp.google.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
index 4b5ba85..845df68 100644 (file)
--- a/arch/x86/mm/mmap.c
+++ b/arch/x86/mm/mmap.c
@@ -75,9 +75,9 @@ 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;
 }