[PATCH v5 3/6] mm: simplify compat_sys_move_pages

[Arnd Bergmann]

From: Arnd Bergmann <a...@arndb.de>

The compat move_pages() implementation uses compat_alloc_user_space()
for converting the pointer array. Moving the compat handling into
the function itself is a bit simpler and lets us avoid the
compat_alloc_user_space() call.

Reviewed-by: Christoph Hellwig <h...@lst.de>
Signed-off-by: Arnd Bergmann <a...@arndb.de>
---
 mm/migrate.c | 45 ++++++++++++++++++++++++++++++---------------
 1 file changed, 30 insertions(+), 15 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index 34a9ad3e0a4f..60634d2653b9 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1820,6 +1820,23 @@ static void do_pages_stat_array(struct mm_struct *mm, 
unsigned long nr_pages,
        mmap_read_unlock(mm);
 }
 
+static int get_compat_pages_array(const void __user *chunk_pages[],
+                                 const void __user * __user *pages,
+                                 unsigned long chunk_nr)
+{
+       compat_uptr_t __user *pages32 = (compat_uptr_t __user *)pages;
+       compat_uptr_t p;
+       int i;
+
+       for (i = 0; i < chunk_nr; i++) {
+               if (get_user(p, pages32 + i))
+                       return -EFAULT;
+               chunk_pages[i] = compat_ptr(p);
+       }
+
+       return 0;
+}
+
 /*
  * Determine the nodes of a user array of pages and store it in
  * a user array of status.
@@ -1839,8 +1856,15 @@ static int do_pages_stat(struct mm_struct *mm, unsigned 
long nr_pages,
                if (chunk_nr > DO_PAGES_STAT_CHUNK_NR)
                        chunk_nr = DO_PAGES_STAT_CHUNK_NR;
 
-               if (copy_from_user(chunk_pages, pages, chunk_nr * 
sizeof(*chunk_pages)))
-                       break;
+               if (in_compat_syscall()) {
+                       if (get_compat_pages_array(chunk_pages, pages,
+                                                  chunk_nr))
+                               break;
+               } else {
+                       if (copy_from_user(chunk_pages, pages,
+                                     chunk_nr * sizeof(*chunk_pages)))
+                               break;
+               }
 
                do_pages_stat_array(mm, chunk_nr, chunk_pages, chunk_status);
 
@@ -1945,23 +1969,14 @@ SYSCALL_DEFINE6(move_pages, pid_t, pid, unsigned long, 
nr_pages,
 
 #ifdef CONFIG_COMPAT
 COMPAT_SYSCALL_DEFINE6(move_pages, pid_t, pid, compat_ulong_t, nr_pages,
-                      compat_uptr_t __user *, pages32,
+                      compat_uptr_t __user *, pages,
                       const int __user *, nodes,
                       int __user *, status,
                       int, flags)
 {
-       const void __user * __user *pages;
-       int i;
-
-       pages = compat_alloc_user_space(nr_pages * sizeof(void *));
-       for (i = 0; i < nr_pages; i++) {
-               compat_uptr_t p;
-
-               if (get_user(p, pages32 + i) ||
-                       put_user(compat_ptr(p), pages + i))
-                       return -EFAULT;
-       }
-       return kernel_move_pages(pid, nr_pages, pages, nodes, status, flags);
+       return kernel_move_pages(pid, nr_pages,
+                                (const void __user *__user *)pages,
+                                nodes, status, flags);
 }
 #endif /* CONFIG_COMPAT */
 
-- 
2.29.2