From: Hou Tao <houtao1@huawei.com>
To: Josef Bacik <josef@toxicpanda.com>, Jens Axboe <axboe@kernel.dk>,
<linux-block@vger.kernel.org>
Cc: <nbd@other.debian.org>, <hch@lst.de>, <houtao1@huawei.com>
Subject: [PATCH v2 3/3] nbd: fix race between nbd_alloc_config() and module removal
Date: Sat, 4 Sep 2021 20:25:19 +0800 [thread overview]
Message-ID: <20210904122519.1963983-4-houtao1@huawei.com> (raw)
In-Reply-To: <20210904122519.1963983-1-houtao1@huawei.com>
When nbd module is being removing, nbd_alloc_config() may be
called concurrently by nbd_genl_connect(), although try_module_get()
will return false, but nbd_alloc_config() doesn't handle it.
The race may lead to the leak of nbd_config and its related
resources (e.g, recv_workq) and oops in nbd_read_stat() due
to the unload of nbd module as shown below:
BUG: kernel NULL pointer dereference, address: 0000000000000040
Oops: 0000 [#1] SMP PTI
CPU: 5 PID: 13840 Comm: kworker/u17:33 Not tainted 5.14.0+ #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996)
Workqueue: knbd16-recv recv_work [nbd]
RIP: 0010:nbd_read_stat.cold+0x130/0x1a4 [nbd]
Call Trace:
recv_work+0x3b/0xb0 [nbd]
process_one_work+0x1ed/0x390
worker_thread+0x4a/0x3d0
kthread+0x12a/0x150
ret_from_fork+0x22/0x30
Fixing it by checking the return value of try_module_get()
in nbd_alloc_config(). As nbd_alloc_config() may return ERR_PTR(-ENODEV),
assign nbd->config only when nbd_alloc_config() succeeds to ensure
the value of nbd->config is binary (valid or NULL).
Also adding a debug message to check the reference counter
of nbd_config during module removal.
Signed-off-by: Hou Tao <houtao1@huawei.com>
---
drivers/block/nbd.c | 28 +++++++++++++++++++---------
1 file changed, 19 insertions(+), 9 deletions(-)
diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index cedd3648e1a7..fa6c069b79dc 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -1473,15 +1473,20 @@ static struct nbd_config *nbd_alloc_config(void)
{
struct nbd_config *config;
+ if (!try_module_get(THIS_MODULE))
+ return ERR_PTR(-ENODEV);
+
config = kzalloc(sizeof(struct nbd_config), GFP_NOFS);
- if (!config)
- return NULL;
+ if (!config) {
+ module_put(THIS_MODULE);
+ return ERR_PTR(-ENOMEM);
+ }
+
atomic_set(&config->recv_threads, 0);
init_waitqueue_head(&config->recv_wq);
init_waitqueue_head(&config->conn_wait);
config->blksize = NBD_DEF_BLKSIZE;
atomic_set(&config->live_connections, 0);
- try_module_get(THIS_MODULE);
return config;
}
@@ -1508,12 +1513,13 @@ static int nbd_open(struct block_device *bdev, fmode_t mode)
mutex_unlock(&nbd->config_lock);
goto out;
}
- config = nbd->config = nbd_alloc_config();
- if (!config) {
- ret = -ENOMEM;
+ config = nbd_alloc_config();
+ if (IS_ERR(config)) {
+ ret = PTR_ERR(config);
mutex_unlock(&nbd->config_lock);
goto out;
}
+ nbd->config = config;
refcount_set(&nbd->config_refs, 1);
refcount_inc(&nbd->refs);
mutex_unlock(&nbd->config_lock);
@@ -1905,13 +1911,14 @@ static int nbd_genl_connect(struct sk_buff *skb, struct genl_info *info)
nbd_put(nbd);
return -EINVAL;
}
- config = nbd->config = nbd_alloc_config();
- if (!nbd->config) {
+ config = nbd_alloc_config();
+ if (IS_ERR(config)) {
mutex_unlock(&nbd->config_lock);
nbd_put(nbd);
pr_err("nbd: couldn't allocate config\n");
- return -ENOMEM;
+ return PTR_ERR(config);
}
+ nbd->config = config;
refcount_set(&nbd->config_refs, 1);
set_bit(NBD_RT_BOUND, &config->runtime_flags);
@@ -2486,6 +2493,9 @@ static void __exit nbd_cleanup(void)
while (!list_empty(&del_list)) {
nbd = list_first_entry(&del_list, struct nbd_device, list);
list_del_init(&nbd->list);
+ if (refcount_read(&nbd->config_refs))
+ pr_err("possibly leaking nbd_config (ref %d)\n",
+ refcount_read(&nbd->config_refs));
if (refcount_read(&nbd->refs) != 1)
pr_err("possibly leaking a device\n");
nbd_put(nbd);
--
2.29.2
next prev parent reply other threads:[~2021-09-04 12:12 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-04 12:25 [PATCH v2 0/3] fix races between nbd setup and module removal Hou Tao
2021-09-04 12:25 ` [PATCH v2 1/3] nbd: use pr_err to output error message Hou Tao
2021-09-06 9:27 ` Christoph Hellwig
2021-09-04 12:25 ` [PATCH v2 2/3] nbd: call genl_unregister_family() first in nbd_cleanup() Hou Tao
2021-09-06 9:27 ` Christoph Hellwig
2021-09-04 12:25 ` Hou Tao [this message]
2021-09-06 9:30 ` [PATCH v2 3/3] nbd: fix race between nbd_alloc_config() and module removal Christoph Hellwig
2021-09-06 10:08 ` Hou Tao
2021-09-06 10:25 ` Christoph Hellwig
2021-09-07 3:04 ` Hou Tao
2021-09-08 13:03 ` Hou Tao
2021-09-09 6:40 ` Christoph Hellwig
2021-09-13 4:32 ` Hou Tao
2021-09-13 15:25 ` Christoph Hellwig
2021-09-14 11:42 ` Wouter Verhelst
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20210904122519.1963983-4-houtao1@huawei.com \
--to=houtao1@huawei.com \
--cc=axboe@kernel.dk \
--cc=hch@lst.de \
--cc=josef@toxicpanda.com \
--cc=linux-block@vger.kernel.org \
--cc=nbd@other.debian.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).