Error Handling Affecting kernel-rt-modules package, versions <0:4.18.0-553.22.1.rt7.363.el8_10

Note: Versions mentioned in the description apply only to the upstream kernel-rt-modules package and not the kernel-rt-modules package as distributed by Centos. See How to fix? for Centos:8 relevant fixed versions and status.

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

block: don't call rq_qos_ops->done_bio if the bio isn't tracked

rq_qos framework is only applied on request based driver, so:

1. rq_qos_done_bio() needn't to be called for bio based driver

2. rq_qos_done_bio() needn't to be called for bio which isn't tracked, such as bios ended from error handling code.

Especially in bio_endio():

1. request queue is referred via bio->bi_bdev->bd_disk->queue, which may be gone since request queue refcount may not be held in above two cases

2. q->rq_qos may be freed in blk_cleanup_queue() when calling into __rq_qos_done_bio()

Fix the potential kernel panic by not calling rq_qos_ops->done_bio if the bio isn't tracked. This way is safe because both ioc_rqos_done_bio() and blkcg_iolatency_done_bio() are nop if the bio isn't tracked.

• https://access.redhat.com/security/cve/CVE-2021-47412
• https://git.kernel.org/stable/c/004b8f8a691205a93d9e80d98b786b2b97424d6e
• https://git.kernel.org/stable/c/a647a524a46736786c95cdb553a070322ca096e3