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:
<pre>
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;
}
</pre>
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:
<pre>
if (!opinfo->conn) {
up_read(&fp->f_ci->m_lock);
goto out;
}
ft = &opinfo->sess->file_table;
write_lock(&ft->lock);
</pre>
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.
CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CVSS Score: 9.8
AV:N - ksmbd is the in-kernel SMB server on TCP/445; the UAF is reached from remote SMB2 CREATE (DH2C durable reconnect, then a later AppInstanceId create) via ksmbd_conn_handler_loop() through handle_ksmbd_work(), smb2_open(), ksmbd_reopen_durable_fd(), and ksmbd_close_fd_app_instance_id().
AC:L - The attacker fully drives both sessions: open the same file with durable-v2 RH leases and distinct AppInstanceIds, log off both, reconnect one with DH2C (misbinding the sibling oplock), destroy that session, then CREATE with the other AppInstanceId. No victim-dependent race, heap layout, or rare kernel config is required.
PR:N - SMB2 CREATE needs a session and tree connect, but ksmbd supports guest/anonymous users and guest shares; guest session setup skips NTLMSSP password verification, so a reasonable NAS/IoT deployment lets an unauthenticated network client reach this path without a named account.
UI:N - No victim action is required; the attacker programmatically issues SESSION_SETUP, TREE_CONNECT, CREATE, LOGOFF, DH2C reconnect, and the follow-up AppInstanceId CREATE on their own SMB connections.
S:U - The UAF corrupts ksmbd/kernel heap on the SMB server host and can escalate privileges within that kernel; it does not cross a VM, guest-to-host, container, or IOMMU/DMA security boundary.
C:H - Use-after-free of a ksmbd_session object: after the adopted session is kfree'd in ksmbd_session_destroy(), ksmbd_close_fd_app_instance_id() still sees a live opinfo->conn and dereferences the stale opinfo->sess, enabling arbitrary kernel disclosure via heap reuse.
I:H - The UAF takes write_lock on the freed session's file_table.lock (KASAN 4-byte write) and may idr_remove through the stale table; with heap spray this yields arbitrary kernel writes and control-flow hijacking, matching High integrity for session-object UAF.
A:H - KASAN reports slab-use-after-free in _raw_write_lock from ksmbd_close_fd_app_instance_id during smb2_open on ksmbd-io; the dangling session pointer causes kernel oops or panic on worker threads and is repeatable by resending the CREATE sequence.
| Attack Vector |
Network |
Scope |
Unchanged |
| Attack Complexity |
Low |
Confidentiality Impact |
High |
| Privileges Required |
None |
Integrity Impact |
High |
| User Interaction |
None |
Availability Impact |
High |
AV:N - ksmbd is the in-kernel SMB server on TCP/445; the UAF is reached from remote SMB2 CREATE (DH2C durable reconnect, then a later AppInstanceId create) via ksmbd_conn_handler_loop() through handle_ksmbd_work(), smb2_open(), ksmbd_reopen_durable_fd(), and ksmbd_close_fd_app_instance_id().
AC:L - The attacker fully drives both sessions: open the same file with durable-v2 RH leases and distinct AppInstanceIds, log off both, reconnect one with DH2C (misbinding the sibling oplock), destroy that session, then CREATE with the other AppInstanceId. No victim-dependent race, heap layout, or rare kernel config is required.
PR:N - SMB2 CREATE needs a session and tree connect, but ksmbd supports guest/anonymous users and guest shares; guest session setup skips NTLMSSP password verification, so a reasonable NAS/IoT deployment lets an unauthenticated network client reach this path without a named account.
UI:N - No victim action is required; the attacker programmatically issues SESSION_SETUP, TREE_CONNECT, CREATE, LOGOFF, DH2C reconnect, and the follow-up AppInstanceId CREATE on their own SMB connections.
S:U - The UAF corrupts ksmbd/kernel heap on the SMB server host and can escalate privileges within that kernel; it does not cross a VM, guest-to-host, container, or IOMMU/DMA security boundary.
C:H - Use-after-free of a ksmbd_session object: after the adopted session is kfree'd in ksmbd_session_destroy(), ksmbd_close_fd_app_instance_id() still sees a live opinfo->conn and dereferences the stale opinfo->sess, enabling arbitrary kernel disclosure via heap reuse.
I:H - The UAF takes write_lock on the freed session's file_table.lock (KASAN 4-byte write) and may idr_remove through the stale table; with heap spray this yields arbitrary kernel writes and control-flow hijacking, matching High integrity for session-object UAF.
A:H - KASAN reports slab-use-after-free in _raw_write_lock from ksmbd_close_fd_app_instance_id during smb2_open on ksmbd-io; the dangling session pointer causes kernel oops or panic on worker threads and is repeatable by resending the CREATE sequence.
CVSS 3.1