[PATCH] mm/mempolicy: add node_empty check in SYSC_migrate_pages

[Yisheng Xie]

As Xiaojun reported the ltp of migrate_pages01 will failed on ARCH arm64
system whoes has 4 nodes[0...3], all have memory and CONFIG_NODES_SHIFT=2:

migrate_pages01    0  TINFO  :  test_invalid_nodes
migrate_pages01   14  TFAIL  :  migrate_pages_common.c:45: unexpected failure - returned value = 0, expected: -1
migrate_pages01   15  TFAIL  :  migrate_pages_common.c:55: call succeeded unexpectedly

In this case the test_invalid_nodes of migrate_pages01 will call:
SYSC_migrate_pages as:

migrate_pages(0, , {0x0000000000000001}, 64, , {0x0000000000000010}, 64) = 0

For MAX_NUMNODES is 4, so 0x10 nodemask will tread as empty set which makes
	nodes_subset(*new, node_states[N_MEMORY])

return true, as empty set is subset of any set.

So this is a common issue which also can happens in X86_64 system eg. 8 nodes[0..7],
all with memory and CONFIG_NODES_SHIFT=3. Fix it by adding node_empty check in
SYSC_migrate_pages.

Reported-by: Tan Xiaojun <tanxiaojun@xxxxxxxxxx>
Signed-off-by: Yisheng Xie <xieyisheng1@xxxxxxxxxx>
---
 mm/mempolicy.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index a2af6d5..1dfd3cc 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1388,6 +1388,11 @@ static int copy_nodes_to_user(unsigned long __user *mask, unsigned long maxnode,
 	if (err)
 		goto out;
 
+	if (nodes_empty(*new)) {
+		err = -EINVAL;
+		goto out;
+	}
+
 	/* Find the mm_struct */
 	rcu_read_lock();
 	task = pid ? find_task_by_vpid(pid) : current;
-- 
1.7.12.4