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

From: Aldo Ariel Panzardo <[email protected]>

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.

Fixes f363a0fb134a ("ksmbd: fix app-instance durable supersede session UAF")

Cc [email protected]

Signed-off-by Aldo Ariel Panzardo <[email protected]>

---
  fs/smb/server/vfs_cache.c | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

fs/smb/server/vfs_cache.c +1 -1

index d95c405eab11..1e9d13344825 100644
@@ -1720,7 +1720,7 @@ int ksmbd_reopen_durable_fd(struct ksmbd_work *work, struct ksmbd_file *fp)
  	down_write(&ci->m_lock);
  	list_for_each_entry_rcu(op, &ci->m_op_list, op_entry,
  				lockdep_is_held(&ci->m_lock)) {
-		if (op->conn)
+		if (op->conn || op->o_fp != fp)
  			continue;
  		op->conn = ksmbd_conn_get(fp->conn);
  		op->sess = work->sess;

From: Aldo Ariel Panzardo <[email protected]>

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.

Fixes f363a0fb134a ("ksmbd: fix app-instance durable supersede session UAF")

Cc [email protected]

Signed-off-by Aldo Ariel Panzardo <[email protected]>