block/rq_qos: protect rq_qos apis with a new lock

Overview

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

block/rq_qos: protect rq_qos apis with a new lock

commit 50e34d78815e ("block: disable the elevator int del_gendisk") move rq_qos_exit() from disk_release() to del_gendisk(), this will introduce some problems:

1. If rq_qos_add() is triggered by enabling iocost/iolatency through cgroupfs, then it can concurrent with del_gendisk(), it's not safe to write 'q->rq_qos' concurrently.

2. Activate cgroup policy that is relied on rq_qos will call rq_qos_add() and blkcg_activate_policy(), and if rq_qos_exit() is called in the middle, null-ptr-dereference will be triggered in blkcg_activate_policy().

3. blkg_conf_open_bdev() can call blkdev_get_no_open() first to find the disk, then if rq_qos_exit() from del_gendisk() is done before rq_qos_add(), then memory will be leaked.

This patch add a new disk level mutex 'rq_qos_mutex':

1. The lock will protect rq_qos_exit() directly.

2. For wbt that doesn't relied on blk-cgroup, rq_qos_add() can only be called from disk initialization for now because wbt can't be destructed until rq_qos_exit(), so it's safe not to protect wbt for now. Hoever, in case that rq_qos dynamically destruction is supported in the furture, this patch also protect rq_qos_add() from wbt_init() directly, this is enough because blk-sysfs already synchronize writers with disk removal.

3. For iocost and iolatency, in order to synchronize disk removal and cgroup configuration, the lock is held after blkdev_get_no_open() from blkg_conf_open_bdev(), and is released in blkg_conf_exit(). In order to fix the above memory leak, disk_live() is checked after holding the new lock.

Affected

• Linux >= 50e34d78815e474d410f342fbe783b18192ca518 < f54c4ab8ffecf621ab20fb6d2b194af93616cd7e
• Linux >= 50e34d78815e474d410f342fbe783b18192ca518 < 16398b4638b5cd8c1dc95fc940a1591a801d53ce
• Linux >= 50e34d78815e474d410f342fbe783b18192ca518 < a13bd91be22318768d55470cbc0b0f4488ef9edf
• Linux f28699fafc047ec33299da01e928c3a0073c5cc6
• Linux >= 5.18.8 < 5.19
• Linux 5.19

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.