CVE-2026-89635: ksmbd: only rebind the reopened file's own oplock on durable reconnect

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

ksmbd: only rebind the reopened file's own oplock on durable reconnect

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.

The Linux kernel CVE team has assigned CVE-2026-89635 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 7.2 with commit f363a0fb134a3eb9e47368b1edbd251fd76be84b and fixed in 7.2.4 with commit 74e3ef4630f004c0de40c0540648a5a4033c6c9d
	Issue introduced in 7.2 with commit f363a0fb134a3eb9e47368b1edbd251fd76be84b and fixed in 7.3-rc1 with commit 3f220a0a62e6b9b391c9d1f0e6580b05173cc7f7

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-89635
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	fs/smb/server/vfs_cache.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/74e3ef4630f004c0de40c0540648a5a4033c6c9d
	https://git.kernel.org/stable/c/3f220a0a62e6b9b391c9d1f0e6580b05173cc7f7