[PATCH] mm/mempolicy: fix get_nodes out of bound access

[Tianyu Li]

When user specified more nodes than supported,
get_nodes will access nmask array out of bound.

Fixes: e130242dc351 ("mm: simplify compat numa syscalls")
Signed-off-by: Tianyu Li <tianyu.li@xxxxxxx>
---
 mm/mempolicy.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 0b4ba3ee810e..9f27dc4b66ba 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1388,7 +1388,7 @@ static int get_nodes(nodemask_t *nodes, const unsigned long __user *nmask,
 		unsigned long bits = min_t(unsigned long, maxnode, BITS_PER_LONG);
 		unsigned long t;
 
-		if (get_bitmap(&t, &nmask[maxnode / BITS_PER_LONG], bits))
+		if (get_bitmap(&t, &nmask[(maxnode - 1) / BITS_PER_LONG], bits))
 			return -EFAULT;
 
 		if (maxnode - bits >= MAX_NUMNODES) {
-- 
2.25.1