Commit 87b8d1ad authored Feb 18, 2010 by H. Peter Anvin Committed by Linus Torvalds Feb 21, 2010

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>

parent aea187c4

mm/migrate.c

+15 −21

Original line number	Diff line number	Diff line
		@@ -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;
		}

		/*