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.

Classification

CVE ID: CVE-2025-21643

Affected Products

Vendor: Linux

Product: Linux

Exploit Prediction Scoring System (EPSS)

EPSS Score: 0.04% (probability of being exploited)

EPSS Percentile: 11.67% (scored less or equal to compared to others)

EPSS Date: 2025-02-17 (when was this score calculated)

References

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

Timeline