mm: Make copy_from_user() in migrate.c statically predictable

x86-32 has had a static test for copy_on_user() overflow for a while.
This test currently fails in mm/migrate.c resulting in an
allyesconfig/allmodconfig build failure on x86-32:

In function ‘copy_from_user’,
    inlined from ‘do_pages_stat’ at
    /home/hpa/kernel/git/mm/migrate.c:1012:
/home/hpa/kernel/git/arch/x86/include/asm/uaccess_32.h:212: error:
    call to ‘copy_from_user_overflow’ declared

Make the logic more explicit and therefore easier for gcc to
understand.

v2: rewrite the loop entirely using a more normal structure for a
    chunked-data loop (Linus Torvalds)

Reported-by: Len Brown <lenb@kernel.org>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Reviewed-and-Tested-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Arjan van de Ven <arjan@linux.kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Christoph Lameter <cl@linux-foundation.org>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/migrate.c b/mm/migrate.c
index 9a0db5bbabe4c93c0fce3ee7c24f13f2fbf84dc0..880bd592d38ea47af36f5f9b64323e8814d09f24 100644 (file)
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1002,33 +1002,27 @@ static int do_pages_stat(struct mm_struct *mm, unsigned long nr_pages,
 #define DO_PAGES_STAT_CHUNK_NR 16
        const void __user *chunk_pages[DO_PAGES_STAT_CHUNK_NR];
        int chunk_status[DO_PAGES_STAT_CHUNK_NR];
-       unsigned long i, chunk_nr = DO_PAGES_STAT_CHUNK_NR;
-       int err;
 
-       for (i = 0; i < nr_pages; i += chunk_nr) {
-               if (chunk_nr > nr_pages - i)
-                       chunk_nr = nr_pages - i;
+       while (nr_pages) {
+               unsigned long chunk_nr;
 
-               err = copy_from_user(chunk_pages, &pages[i],
-                                    chunk_nr * sizeof(*chunk_pages));
-               if (err) {
-                       err = -EFAULT;
-                       goto out;
-               }
+               chunk_nr = 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;
 
                do_pages_stat_array(mm, chunk_nr, chunk_pages, chunk_status);
 
-               err = copy_to_user(&status[i], chunk_status,
-                                  chunk_nr * sizeof(*chunk_status));
-               if (err) {
-                       err = -EFAULT;
-                       goto out;
-               }
-       }
-       err = 0;
+               if (copy_to_user(status, chunk_status, chunk_nr * sizeof(*status)))
+                       break;
 
-out:
-       return err;
+               pages += chunk_nr;
+               status += chunk_nr;
+               nr_pages -= chunk_nr;
+       }
+       return nr_pages ? -EFAULT : 0;
 }
 
 /*