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CVE-2025-21643netfs: Fix kernel async DIO

Description

In the Linux kernel, the following vulnerability has been resolved: netfs: Fix kernel async DIO Netfslib needs to be able to handle kernel-initiated asynchronous DIO that is supplied with a bio_vec[] array. Currently, because of the async flag, this gets passed to netfs_extract_user_iter() which throws a warning and fails because it only handles IOVEC and UBUF iterators. This can be triggered through a combination of cifs and a loopback blockdev with something like: mount //my/cifs/share /foo dd if=/dev/zero of=/foo/m0 bs=4K count=1K losetup --sector-size 4096 --direct-io=on /dev/loop2046 /foo/m0 echo hello >/dev/loop2046 This causes the following to appear in syslog: WARNING: CPU: 2 PID: 109 at fs/netfs/iterator.c:50 netfs_extract_user_iter+0x170/0x250 [netfs] and the write to fail. Fix this by removing the check in netfs_unbuffered_write_iter_locked() that causes async kernel DIO writes to be handled as userspace writes. Note that this change relies on the kernel caller maintaining the existence of the bio_vec array (or kvec[] or folio_queue) until the op is complete.

Timeline

  1. ID reserved

    By Linux

  2. · 21 days later

    Published

  3. · 16 months later

    Record updated

Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.

Scores

CVSS scores of CVE-2025-21643, by who scored it
Scored byCVSSScoreVector
NVDNVD · Analyzed3.1Medium5.5CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
EPSS (exploitation in 30 days)
0.21% · top 88% of all CVEs (13 Nov 2026)
Loading the EPSS history…

The list uses the assigner's score when there is one, then CISA's, then NVD's: Medium 5.5.

Affected products

  • Linux · Linux

    • affected 153a9961b551101cd38e94e26cd92fbfd198b19b – < 9f3a265836844eda30bf34c2584b8011fd4f0f49
    • affected 153a9961b551101cd38e94e26cd92fbfd198b19b – < 3f6bc9e3ab9b127171d39f9ac6eca1abb693b731

  • Linux · Linux

    • affected 6.8
    • unaffected < 6.8
    • unaffected 6.12.10 – ≤ 6.12.*
    • unaffected 6.13 – ≤ *

References

References2

Sources

The same CVE in the primary databases and aggregators, to check against.

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Record last updated .