CVE-2025-38534: netfs: Fix copy-to-cache so that it performs collection with ceph+fscache

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.1% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-08-16 · updated 2026-06-17

Description

In the Linux kernel, the following vulnerability has been resolved: netfs: Fix copy-to-cache so that it performs collection with ceph+fscache The netfs copy-to-cache that is used by Ceph with local caching sets up a new request to write data just read to the cache. The request is started and then left to look after itself whilst the app continues. The request gets notified by the backing fs upon completion of the async DIO write, but then tries to wake up the app because NETFS_RREQ_OFFLOAD_COLLECTION isn't set - but the app isn't waiting there, and so the request just hangs. Fix this by setting NETFS_RREQ_OFFLOAD_COLLECTION which causes the notification from the backing filesystem to put the collection onto a work queue instead.

Affected products

Linux kernel: from 6.14 before 6.15.8; 6.16-rc1, 6.16-rc2, 6.16-rc3, 6.16-rc4, 6.16-rc5, 6.16-rc6 — fixed in 6.15.8

How to fix

Upgrade to a fixed version: Linux kernel 6.15.8. Check the vendor advisory for mitigations.

References

Get alerted when CVE-2025-38534 or the next vulnerability affects your stack