Commit 43e43c9e authored Nov 17, 2015 by Junichi Nomura Committed by Mike Snitzer Nov 17, 2015

dm mpath: fix infinite recursion in ioctl when no paths and !queue_if_no_path



In multipath_prepare_ioctl(),
  - pgpath is a path selected from available paths
  - m->queue_io is true if we cannot send a request immediately to
    paths, either because:
      * there is no available path
      * the path group needs activation (pg_init)
          - pg_init is not started
          - pg_init is still running
  - m->queue_if_no_path is true if the device is configured to queue
    I/O if there are no available paths

If !pgpath && !m->queue_if_no_path, the handler should return -EIO.
However in the course of refactoring the condition check has broken
and returns success in that case.  Since bdev points to the dm device
itself, dm_blk_ioctl() calls __blk_dev_driver_ioctl() for itself and
recurses until crash.

You could reproduce the problem like this:

  # dmsetup create mp --table '0 1024 multipath 0 0 0 0'
  # sg_inq /dev/mapper/mp
  <crash>
  [  172.648615] BUG: unable to handle kernel paging request at fffffffc81b10268
  [  172.662843] PGD 19dd067 PUD 0
  [  172.666269] Thread overran stack, or stack corrupted
  [  172.671808] Oops: 0000 [#1] SMP
  ...

Fix the condition check with some clarifications.

Fixes: e56f81e0 ("dm: refactor ioctl handling")
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

parent 647a20d5

drivers/md/dm-mpath.c

+15 −13

Original line number	Diff line number	Diff line
		@@ -1537,28 +1537,30 @@ static int multipath_prepare_ioctl(struct dm_target *ti,
		struct block_device *bdev, fmode_t mode)
		{
		struct multipath *m = ti->private;
		struct pgpath *pgpath;
		unsigned long flags;
		int r;

		r = 0;

		spin_lock_irqsave(&m->lock, flags);

		if (!m->current_pgpath)
		__choose_pgpath(m, 0);

		pgpath = m->current_pgpath;

		if (pgpath) {
		*bdev = pgpath->path.dev->bdev;
		*mode = pgpath->path.dev->mode;
		if (m->current_pgpath) {
		if (!m->queue_io) {
		*bdev = m->current_pgpath->path.dev->bdev;
		*mode = m->current_pgpath->path.dev->mode;
		r = 0;
		} else {
		/* pg_init has not started or completed */
		r = -ENOTCONN;
		}

		if ((pgpath && m->queue_io) \|\| (!pgpath && m->queue_if_no_path))
		} else {
		/* No path is available */
		if (m->queue_if_no_path)
		r = -ENOTCONN;
		else if (!*bdev)
		else
		r = -EIO;
		}

		spin_unlock_irqrestore(&m->lock, flags);

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