Merge v7.1.5linux-rolling-stable

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 21 insertions, 3 deletions

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index e178fe19973e..1334c411c722 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -735,7 +735,16 @@ static struct table_device *open_table_device(struct mapped_device *md,
 		return ERR_PTR(-ENOMEM);
 	refcount_set(&td->count, 1);
 
-	bdev_file = bdev_file_open_by_dev(dev, mode, _dm_claim_ptr, NULL);
+	/*
+	 * Open the backing device with kernel rather than caller
+	 * credentials. Otherwise the caller's credentials would be
+	 * pinned in bdev_file->f_cred until the table device is closed.
+	 * That would keep the caller's thread keyring alive long beyond the
+	 * lifetime of the caller, breaking userspace expectation (e.g.
+	 * cryptsetup(8) leaking the LUKS volume key).
+	 */
+	scoped_with_kernel_creds()
+		bdev_file = bdev_file_open_by_dev(dev, mode, _dm_claim_ptr, NULL);
 	if (IS_ERR(bdev_file)) {
 		r = PTR_ERR(bdev_file);
 		goto out_free_td;
@@ -2098,8 +2107,17 @@ static bool dm_poll_dm_io(struct dm_io *io, struct io_comp_batch *iob,
 	WARN_ON_ONCE(!dm_tio_is_normal(&io->tio));
 
 	/* don't poll if the mapped io is done */
-	if (atomic_read(&io->io_count) > 1)
-		bio_poll(&io->tio.clone, iob, flags);
+	if (atomic_read(&io->io_count) > 1) {
+		/*
+		 * DM hides the target queues from the upper poller, which may
+		 * decide it is safe to spin on a single stacked queue.  Do not
+		 * pass that spinning policy down to a target queue: one slow
+		 * clone could keep the task inside dm_poll_bio() for a long
+		 * time.  Poll target bios once and let the caller decide
+		 * whether to keep polling, reap completions or reschedule.
+		 */
+		bio_poll(&io->tio.clone, iob, flags | BLK_POLL_ONESHOT);
+	}
 
 	/* bio_poll holds the last reference */
 	return atomic_read(&io->io_count) == 1;