[PATCH 5.18 0719/1095] mm/mempolicy: fix get_nodes out of bound access

[Greg Kroah-Hartman]

From: Tianyu Li <tianyu.li@xxxxxxx>

[ Upstream commit 000eca5d044d1ee23b4ca311793cf3fc528da6c6 ]

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

Link: https://lkml.kernel.org/r/20220601093211.2970565-1-tianyu.li@xxxxxxx
Fixes: e130242dc351 ("mm: simplify compat numa syscalls")
Signed-off-by: Tianyu Li <tianyu.li@xxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 mm/mempolicy.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index b27e8d71cda3..c1ccc89845f4 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1387,7 +1387,7 @@ 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) {
-- 
2.35.1