CVE-2025-21643: netfs: Fix kernel async DIO
First published: Sun Jan 19 2025(Updated: )
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.
Credit: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
| Affected Software | Affected Version | How to fix |
|---|---|---|
| Linux Kernel | ||
| debian/linux | 5.10.223-1 5.10.234-1 6.1.129-1 6.1.128-1 6.12.20-1 6.12.21-1 |
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Reference Links
- https://git.kernel.org/stable/c/3f6bc9e3ab9b127171d39f9ac6eca1abb693b731
- https://git.kernel.org/stable/c/9f3a265836844eda30bf34c2584b8011fd4f0f49
- https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2025-21643
- https://nvd.nist.gov/vuln/detail/CVE-2025-21643
- https://launchpad.net/bugs/cve/CVE-2025-21643
- https://security-tracker.debian.org/tracker/CVE-2025-21643
- https://ubuntu.com/security/CVE-2025-21643
- https://git.kernel.org/linus/3f6bc9e3ab9b127171d39f9ac6eca1abb693b731
Frequently Asked Questions
What is the severity of CVE-2025-21643?
The severity of CVE-2025-21643 is considered medium due to its potential impact on data integrity.
How do I fix CVE-2025-21643?
To fix CVE-2025-21643, update to the latest patch released by the Linux kernel maintainers.
What versions of the Linux kernel are affected by CVE-2025-21643?
CVE-2025-21643 affects specific versions of the Linux kernel that utilize the netfs component for asynchronous DIO.
Is CVE-2025-21643 exploitable remotely?
CVE-2025-21643 is not directly exploitable remotely as it requires local access to the affected system.
What should I monitor related to CVE-2025-21643?
Monitor kernel logs for unusual activity that may indicate attempts to exploit vulnerabilities like CVE-2025-21643.
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