[RFC v2 1/5] mm/migrate: fix do_pages_move for compat pointers

[Gregory Price]

do_pages_move does not handle compat pointers for the page list.
correctly.  Add in_compat_syscall check and appropriate get_user
fetch when iterating the page list.

Signed-off-by: Gregory Price <gregory.price@xxxxxxxxxxxx>
Reported-by: Arnd Bergmann <arnd@xxxxxxxx>
Co-developed-by: Arnd Bergmann <arnd@xxxxxxxx>
---
 mm/migrate.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index b7fa020003f3..a0b0c5a7f8a5 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2159,6 +2159,7 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
 			 const int __user *nodes,
 			 int __user *status, int flags)
 {
+	compat_uptr_t __user *compat_pages = (void __user *)pages;
 	int current_node = NUMA_NO_NODE;
 	LIST_HEAD(pagelist);
 	int start, i;
@@ -2171,8 +2172,17 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
 		int node;
 
 		err = -EFAULT;
-		if (get_user(p, pages + i))
-			goto out_flush;
+		if (in_compat_syscall()) {
+			compat_uptr_t cp;
+
+			if (get_user(cp, compat_pages + i))
+				goto out_flush;
+
+			p = compat_ptr(cp);
+		} else {
+			if (get_user(p, pages + i))
+				goto out_flush;
+		}
 		if (get_user(node, nodes + i))
 			goto out_flush;
 
-- 
2.39.1