linux-kernel - [PATCH v2] dm ioctl: fix hang in early create error condition

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Date:   Wed, 15 May 2019 13:50:54 -0300
From:   Helen Koike <helen.koike@...labora.com>
To:     dm-devel@...hat.com
Cc:     kernel@...labora.com, Helen Koike <helen.koike@...labora.com>,
        stable@...r.kernel.org, Mike Snitzer <snitzer@...hat.com>,
        linux-kernel@...r.kernel.org, Alasdair Kergon <agk@...hat.com>
Subject: [PATCH v2] dm ioctl: fix hang in early create error condition

The dm_early_create() function (which deals with "dm-mod.create=" kernel
command line option) calls dm_hash_insert() who gets an extra reference
to the md object.

In case of failure, this reference wasn't being released, causing
dm_destroy() to hang, thus hanging the whole boot process.

Fix this by calling __hash_remove() in the error path.

Fixes: 6bbc923dfcf57d ("dm: add support to directly boot to a mapped device")
Cc: stable@...r.kernel.org
Signed-off-by: Helen Koike <helen.koike@...labora.com>

---
Hi,

I also tested this patch version with the new test case in the following test
script:

https://gitlab.collabora.com/koike/dm-cmdline-test/commit/d2d7a0ee4a49931cdb59f08a837b516c2d5d743d

Thanks
Helen

Changes in v2:
- instead of modifying dm_hash_insert() to return the hash cell, use
__get_name_cell(dmi->name) instead.

 drivers/md/dm-ioctl.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index c740153b4e52..1e03bc89e20f 100644
--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -2069,7 +2069,7 @@ int __init dm_early_create(struct dm_ioctl *dmi,
 	/* alloc table */
 	r = dm_table_create(&t, get_mode(dmi), dmi->target_count, md);
 	if (r)
-		goto err_destroy_dm;
+		goto err_hash_remove;
 
 	/* add targets */
 	for (i = 0; i < dmi->target_count; i++) {
@@ -2116,6 +2116,10 @@ int __init dm_early_create(struct dm_ioctl *dmi,
 
 err_destroy_table:
 	dm_table_destroy(t);
+err_hash_remove:
+	(void) __hash_remove(__get_name_cell(dmi->name));
+	/* release reference from __get_name_cell */
+	dm_put(md);
 err_destroy_dm:
 	dm_put(md);
 	dm_destroy(md);
-- 
2.20.1