Description

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

md: fix deadlock between mddev_suspend and flush bio

Deadlock occurs when mddev is being suspended while some flush bio is in
progress. It is a complex issue.

T1. the first flush is at the ending stage, it clears 'mddev->flush_bio'
and tries to submit data, but is blocked because mddev is suspended
by T4.
T2. the second flush sets 'mddev->flush_bio', and attempts to queue
md_submit_flush_data(), which is already running (T1) and won't
execute again if on the same CPU as T1.
T3. the third flush inc active_io and tries to flush, but is blocked because
'mddev->flush_bio' is not NULL (set by T2).
T4. mddev_suspend() is called and waits for active_io dec to 0 which is inc
by T3.

T1 T2 T3 T4
(flush 1) (flush 2) (third 3) (suspend)
md_submit_flush_data
mddev->flush_bio = NULL;
.
. md_flush_request
. mddev->flush_bio = bio
. queue submit_flushes
. .
. . md_handle_request
. . active_io + 1
. . md_flush_request
. . wait !mddev->flush_bio
. .
. . mddev_suspend
. . wait !active_io
. .
. submit_flushes
. queue_work md_submit_flush_data
. //md_submit_flush_data is already running (T1)
.
md_handle_request
wait resume

The root issue is non-atomic inc/dec of active_io during flush process.
active_io is dec before md_submit_flush_data is queued, and inc soon
after md_submit_flus...

Classification

CVE ID: CVE-2024-43855

Affected Products

Vendor: Linux

Product: Linux

Exploit Prediction Scoring System (EPSS)

EPSS Score: 0.03% (probability of being exploited)

EPSS Percentile: 7.75% (scored less or equal to compared to others)

EPSS Date: 2025-05-05 (when was this score calculated)

Stakeholder-Specific Vulnerability Categorization (SSVC)

SSVC Exploitation: none

SSVC Technical Impact: partial

SSVC Automatable: false

References

https://nvd.nist.gov/vuln/detail/CVE-2024-43855
https://git.kernel.org/stable/c/32226070813140234b6c507084738e8e8385c5c6
https://git.kernel.org/stable/c/2d0738a8322bf4e5bfe693d16b3111928a9ccfbf
https://git.kernel.org/stable/c/ca963eefbc3331222b6121baa696d49ba2008811
https://git.kernel.org/stable/c/611d5cbc0b35a752e657a83eebadf40d814d006b

Timeline