[PATCH RFC v2 1/4] mm/mempolicy: Fix get_nodes() mask miscalculation

[Yisheng Xie <xieyisheng1@huawei.com>]

It appears there is a nodemask miscalculation in the get_nodes()
function in mm/mempolicy.c.  This bug has two effects:

1. It is impossible to specify a length 1 nodemask.
2. It is impossible to specify a nodemask containing the last node.

Brent have submmit a patch before v2.6.12, however, Andi revert his
changed for ABI problem. I just resent this patch as RFC, for do not
clear about what's the problem Andi have met.

As manpage of set_mempolicy, If the value of maxnode is zero, the
nodemask argument is ignored. but we should not ignore the nodemask
when maxnode is 1.

Signed-off-by: Yisheng Xie <xieyisheng1@huawei.com>
---
 mm/mempolicy.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index a2af6d5..613e9d0 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1265,7 +1265,6 @@ static int get_nodes(nodemask_t *nodes, const unsigned long __user *nmask,
 	unsigned long nlongs;
 	unsigned long endmask;
 
-	--maxnode;
 	nodes_clear(*nodes);
 	if (maxnode == 0 || !nmask)
 		return 0;
-- 
1.7.12.4

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