{"id":"DEBIAN-CVE-2025-21643","details":"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 \u003e/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.","modified":"2026-08-27T23:05:11.688432148Z","published":"2025-01-19T11:15:09.870Z","upstream":["CVE-2025-21643"],"references":[{"type":"ADVISORY","url":"https://security-tracker.debian.org/tracker/CVE-2025-21643"}],"affected":[{"package":{"name":"linux","ecosystem":"Debian:13","purl":"pkg:deb/debian/linux?arch=source&distro=trixie"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"6.12.10-1"}]}],"ecosystem_specific":{"urgency":"not yet assigned"},"database_specific":{"source":"https://storage.googleapis.com/osv-test-debian-osv/debian-cve-osv/DEBIAN-CVE-2025-21643.json"}},{"package":{"name":"linux","ecosystem":"Debian:14","purl":"pkg:deb/debian/linux?arch=source&distro=forky"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"6.12.10-1"}]}],"ecosystem_specific":{"urgency":"not yet assigned"},"database_specific":{"source":"https://storage.googleapis.com/osv-test-debian-osv/debian-cve-osv/DEBIAN-CVE-2025-21643.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H"}]}