From: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Date: Wed, 25 Aug 2021 18:31:05 +0200
Subject: [PATCH] nbd: prevent IDR lookups from finding partially initialized
devices
Git-commit: 75b7f62aa65d5c496391ec2c3db3561aaf81a403
Patch-mainline: v5.15-rc1
References: jsc#PED-1183
Previously nbd_index_mutex was held during whole add/remove/lookup
operations in order to guarantee that partially initialized devices are
not reachable via idr_find() or idr_for_each(). But now that partially
initialized devices become reachable as soon as idr_alloc() succeeds,
we need to skip partially initialized devices. Since it seems that
all functions use refcount_inc_not_zero(&nbd->refs) in order to skip
destroying devices, update nbd->refs from zero to non-zero as the last
step of device initialization in order to also skip partially initialized
devices.
Fixes: 6e4df4c64881 ("nbd: reduce the nbd_index_mutex scope")
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
[hch: split from a larger patch, added comments]
Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20210825163108.50713-4-hch@lst.de
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Acked-by: Hannes Reinecke <hare@suse.com>
---
drivers/block/nbd.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index 938ca7f5a11f..b1ed2360ef32 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -1747,7 +1747,11 @@ static struct nbd_device *nbd_dev_add(int index, unsigned int refs)
mutex_init(&nbd->config_lock);
refcount_set(&nbd->config_refs, 0);
- refcount_set(&nbd->refs, refs);
+ /*
+ * Start out with a zero references to keep other threads from using
+ * this device until it is fully initialized.
+ */
+ refcount_set(&nbd->refs, 0);
INIT_LIST_HEAD(&nbd->list);
disk->major = NBD_MAJOR;
@@ -1766,6 +1770,11 @@ static struct nbd_device *nbd_dev_add(int index, unsigned int refs)
disk->private_data = nbd;
sprintf(disk->disk_name, "nbd%d", index);
add_disk(disk);
+
+ /*
+ * Now publish the device.
+ */
+ refcount_set(&nbd->refs, refs);
nbd_total_devices++;
return nbd;
--
2.35.3