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    SubjectRe: [PATCH] mm: Make copy_from_user() in migrate.c statically predictable
    On Thu, 18 Feb 2010, H. Peter Anvin wrote:

    > Updated patch, which compile-tests for me, attached.

    Looks ok.

    Acked-by: Christoph Lameter <cl@linux-foundation.org>
    >From 90585838c29ef62fd80e776d0985c40bbffd852a Mon Sep 17 00:00:00 2001
    From: H. Peter Anvin <hpa@zytor.com>
    Date: Thu, 18 Feb 2010 16:13:40 -0800
    Subject: [PATCH] mm: Make copy_from_user() in migrate.c statically predictable
    MIME-Version: 1.0
    Content-Type: text/plain; charset=UTF-8
    Content-Transfer-Encoding: 8bit

    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: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: H. Peter Anvin <hpa@zytor.com>
    Cc: Arjan van de Ven <arjan@linux.kernel.org>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
    Cc: Christoph Lameter <cl@linux-foundation.org>
    Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
    Cc: Rik van Riel <riel@redhat.com>
    ---
    mm/migrate.c | 36 +++++++++++++++---------------------
    1 files changed, 15 insertions(+), 21 deletions(-)

    diff --git a/mm/migrate.c b/mm/migrate.c
    index 9a0db5b..880bd59 100644
    --- 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;
    }

    /*
    --
    1.6.5.2

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