CVE-2025-21643

netfs: 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.

N/A

CVSS

Severity:

EPSS 0.03%

Affected: Linux Linux

References

Link	Tags
https://git.kernel.org/stable/c/9f3a265836844eda30bf34c2584b8011fd4f0f49
https://git.kernel.org/stable/c/3f6bc9e3ab9b127171d39f9ac6eca1abb693b731

Frequently Asked Questions

What is the severity of CVE-2025-21643?: CVE-2025-21643 has not yet been assigned a CVSS score.
How to fix CVE-2025-21643?: To fix CVE-2025-21643, make sure you are using an up-to-date version of the affected component(s) by checking the vendor release notes. As for now, there are no other specific guidelines available.
Is CVE-2025-21643 being actively exploited in the wild?: As for now, there are no information to confirm that CVE-2025-21643 is being actively exploited. According to its EPSS score, there is a ~0% probability that this vulnerability will be exploited by malicious actors in the next 30 days.
What software or system is affected by CVE-2025-21643?: CVE-2025-21643 affects Linux Linux, Linux Linux.

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