FAILED: patch "[PATCH] nbd: freeze the queue while we're adding connections" failed to apply to 4.4-stable tree

FAILED: patch "[PATCH] nbd: freeze the queue while we're adding connections" failed to apply to 4.4-stable tree

[gregkh]

The patch below does not apply to the 4.4-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From b98e762e3d71e893b221f871825dc64694cfb258 Mon Sep 17 00:00:00 2001
From: Josef Bacik <josef@toxicpanda.com>
Date: Mon, 25 Jan 2021 12:21:02 -0500
Subject: [PATCH] nbd: freeze the queue while we're adding connections

When setting up a device, we can krealloc the config->socks array to add
new sockets to the configuration.  However if we happen to get a IO
request in at this point even though we aren't setup we could hit a UAF,
as we deref config->socks without any locking, assuming that the
configuration was setup already and that ->socks is safe to access it as
we have a reference on the configuration.

But there's nothing really preventing IO from occurring at this point of
the device setup, we don't want to incur the overhead of a lock to
access ->socks when it will never change while the device is running.
To fix this UAF scenario simply freeze the queue if we are adding
sockets.  This will protect us from this particular case without adding
any additional overhead for the normal running case.

Cc: stable@vger.kernel.org
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index 6727358e147d..e6ea5d344f87 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -1022,6 +1022,12 @@ static int nbd_add_socket(struct nbd_device *nbd, unsigned long arg,
 	if (!sock)
 		return err;
 
+	/*
+	 * We need to make sure we don't get any errant requests while we're
+	 * reallocating the ->socks array.
+	 */
+	blk_mq_freeze_queue(nbd->disk->queue);
+
 	if (!netlink && !nbd->task_setup &&
 	    !test_bit(NBD_RT_BOUND, &config->runtime_flags))
 		nbd->task_setup = current;
@@ -1060,10 +1066,12 @@ static int nbd_add_socket(struct nbd_device *nbd, unsigned long arg,
 	nsock->cookie = 0;
 	socks[config->num_connections++] = nsock;
 	atomic_inc(&config->live_connections);
+	blk_mq_unfreeze_queue(nbd->disk->queue);
 
 	return 0;
 
 put_socket:
+	blk_mq_unfreeze_queue(nbd->disk->queue);
 	sockfd_put(sock);
 	return err;
 }