5.5 - CVE-2024-26899

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

block: fix deadlock between bd_link_disk_holder and partition scan

'open_mutex' of gendisk is used to protect open/close block devices. But in bd_link_disk_holder(), it is used to protect the creation of symlink between holding disk and slave bdev, which introduces some issues.

When bd_link_disk_holder() is called, the driver is usually in the process of initialization/modification and may suspend submitting io. At this time, any io hold 'open_mutex', such as scanning partitions, can cause deadlocks. For example, in raid:

T1 T2 bdev_open_by_dev
lock open_mutex [1]
...
efi_partition
...
md_submit_bio
md_ioctl mddev_syspend
-> suspend all io
md_add_new_disk
bind_rdev_to_array
bd_link_disk_holder
try lock open_mutex [2]
md_handle_request
-> wait mddev_resume

T1 scan partition, T2 add a new device to raid. T1 waits for T2 to resume mddev, but T2 waits for open_mutex held by T1. Deadlock occurs.

Fix it by introducing a local mutex 'blk_holder_mutex' to replace 'open_mutex'.