CVE-2022-49300

In the Linux kernel, the following vulnerability has been resolved:

nbd: fix race between nbd_alloc_config() and module removal

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.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.