CVE-2026-89635

What the bug is

ksmbd_reopen_durable_fd() walks the inode's m_op_list and rebinds every detached oplock to the reconnecting session: list_for_each_entry_rcu(op, &ci->m_op_list, op_entry, lockdep_is_held(&ci->m_lock)) { if (op->conn) continue; op->conn = ksmbd_conn_get(fp->conn); op->sess = work->sess; } The only key is op->conn == NULL, which every detached durable handle on that inode matches, not just the one owned by fp. When two sessions hold durable handles on the same file and both disconnect, reconnecting one of them adopts the other session's oplock: op->sess is overwritten with the reconnecting session without taking a reference on it, while op->conn pins the connection. The sibling teardown path, session_fd_check(), keys on the identity of the connection being torn down (op->conn == conn) rather than on shared state, and so does not have this problem. Once the adopting session is destroyed, ksmbd_session_destroy() frees it while the foreign oplock still points at it. The reader in ksmbd_close_fd_app_instance_id() validates only opinfo->conn, which is still live thanks to the reference taken above, and then dereferences the stale session: if (!opinfo->conn) { up_read(&fp->f_ci->m_lock); goto out; } ft = &opinfo->sess->file_table; write_lock(&ft->lock); BUG: KASAN: slab-use-after-free in _raw_write_lock+0x74/0xd0 Write of size 4 at addr ffff88810a970528 by task kworker/0:0/9 Workqueue: ksmbd-io handle_ksmbd_work Call Trace: _raw_write_lock+0x74/0xd0 ksmbd_close_fd_app_instance_id+0x183/0x410 smb2_open+0x1346/0x4430 handle_ksmbd_work+0x2bb/0x7b0 Reached from an authenticated session against a share with the default durable-handle and oplock configuration: two sessions open the same file with a durable-v2 handle and an RH lease under distinct AppInstanceIds, both log off, one reconnects with DH2C, and a later durable-v2 create carrying the other AppInstanceId walks into the freed session. Constrain the loop to the oplock owned by the file being reopened.

Where it lives

The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.

fs/smb/server/vfs_cache.c

What this is

KERNEL SMB3 SERVER (KSMBD)MAINTAINERS section matched on fs/smb/server/ · linux-cifs@vger.kernel.org · Maintained

Kernel module

ksmbd

Check it on the machine

grep -wE 'CONFIG_SMBFS|CONFIG_SMB_SERVER' /boot/config-$(uname -r)

Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.

lsmod | grep -w ksmbd

Prints a line if that module is loaded right now, and nothing if it is not. One that is not loaded can still be loaded later by anything that needs it.

Show whether Debian builds this, per release

Debian builds this as a loadable module. Every release below compiles it as a module on every flavour, so whether the code is in the running kernel depends on whether that module is loaded.

• bookworm, trixie, forky, sidm

m

a loadable module on every flavour - check lsmod, can be blacklisted

Build switches

CONFIG_SMBFS, CONFIG_SMB_SERVER

Reads as

all on means the file is compiled; any one off means it is not.

From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages

Signals

Published

2026-09-11 (37 days ago)source

CVSS

9.8 critical
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsource recompute it

Attack vector

network (AV:N)source

EPSS

0.55%, higher than 45.0% of all CVEssource

CISA KEV

not listedthe KEV catalogue

Debian urgency

unimportantsource

Subsystem

fs/smb

Upstream fixes

The versions the CNA records as introducing and fixing this, and the commit for each. source

Introduced	Fixed in	Commit
7.2	7.2.4	74e3ef4630f0
7.2	7.3	3f220a0a62e6