mm/migrate: fix do_pages_move for compat pointers

commit 229e2253766c7cdfe024f1fe280020cc4711087c upstream.

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.

It makes the syscall in compat mode (32-bit userspace, 64-bit kernel)
work the same way as the native 32-bit syscall again, restoring the
behavior before my broken commit 5b1b561ba73c ("mm: simplify
compat_sys_move_pages").

More specifically, my patch moved the parsing of the 'pages' array from
the main entry point into do_pages_stat(), which left the syscall
working correctly for the 'stat' operation (nodes = NULL), while the
'move' operation (nodes != NULL) is now missing the conversion and
interprets 'pages' as an array of 64-bit pointers instead of the
intended 32-bit userspace pointers.

It is possible that nobody noticed this bug because the few
applications that actually call move_pages are unlikely to run in
compat mode because of their large memory requirements, but this
clearly fixes a user-visible regression and should have been caught by
ltp.

Link: https://lkml.kernel.org/r/20231003144857.752952-1-gregory.price@memverge.com
Fixes: 5b1b561ba73c ("mm: simplify compat_sys_move_pages")
Signed-off-by: Gregory Price <gregory.price@memverge.com>
Reported-by: Arnd Bergmann <arnd@arndb.de>
Co-developed-by: Arnd Bergmann <arnd@arndb.de>
Cc: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/mm/migrate.c b/mm/migrate.c
index 8d5c0dc..9372a82 100644 (file)
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1787,6 +1787,7 @@ 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;
@@ -1800,8 +1801,17 @@ 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;
                addr = (unsigned long)untagged_addr(p);