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    Subject[patch 037/100] dm io: make sync_io uninterruptible
    -stable review patch.  If anyone has any objections, please let us know.
    ---------------------

    From: Mikulas Patocka <mpatocka@redhat.com>

    upstream commit: b64b6bf4fd8b678a9f8477c11773c38a0a246a6d

    If someone sends signal to a process performing synchronous dm-io call,
    the kernel may crash.

    The function sync_io attempts to exit with -EINTR if it has pending signal,
    however the structure "io" is allocated on stack, so already submitted io
    requests end up touching unallocated stack space and corrupting kernel memory.

    sync_io sets its state to TASK_UNINTERRUPTIBLE, so the signal can't break out
    of io_schedule() --- however, if the signal was pending before sync_io entered
    while (1) loop, the corruption of kernel memory will happen.

    There is no way to cancel in-progress IOs, so the best solution is to ignore
    signals at this point.

    Cc: stable@kernel.org
    Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
    Signed-off-by: Alasdair G Kergon <agk@redhat.com>
    Signed-off-by: Chris Wright <chrisw@sous-sol.org>
    ---
    drivers/md/dm-io.c | 5 +----
    1 file changed, 1 insertion(+), 4 deletions(-)

    --- a/drivers/md/dm-io.c
    +++ b/drivers/md/dm-io.c
    @@ -370,16 +370,13 @@ static int sync_io(struct dm_io_client *
    while (1) {
    set_current_state(TASK_UNINTERRUPTIBLE);

    - if (!atomic_read(&io.count) || signal_pending(current))
    + if (!atomic_read(&io.count))
    break;

    io_schedule();
    }
    set_current_state(TASK_RUNNING);

    - if (atomic_read(&io.count))
    - return -EINTR;
    -
    if (error_bits)
    *error_bits = io.error_bits;



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