CVE-2024-26671

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

blk-mq: fix IO hang from sbitmap wakeup race

In blk_mq_mark_tag_wait(), __add_wait_queue() may be re-ordered

with the following blk_mq_get_driver_tag() in case of getting driver

tag failure.

Then in __sbitmap_queue_wake_up(), waitqueue_active() may not observe

the added waiter in blk_mq_mark_tag_wait() and wake up nothing, meantime

blk_mq_mark_tag_wait() can't get driver tag successfully.

This issue can be reproduced by running the following test in loop, and

fio hang can be observed in < 30min when running it on my test VM

in laptop.

modprobe -r scsi_debug

modprobe scsi_debug delay=0 dev_size_mb=4096 max_queue=1 host_max_queue=1 submit_queues=4

dev=`ls -d /sys/bus/pseudo/drivers/scsi_debug/adapter*/host*/target*/*/block/* | head -1 | xargs basename`

fio --filename=/dev/"$dev" --direct=1 --rw=randrw --bs=4k --iodepth=1 \

--runtime=100 --numjobs=40 --time_based --name=test \

--ioengine=libaio

Fix the issue by adding one explicit barrier in blk_mq_mark_tag_wait(), which

is just fine in case of running out of tag.