Commit 7aa8804c authored by Namjae Jeon's avatar Namjae Jeon Committed by Steve French
Browse files

ksmbd: fix user-after-free from session log off 



There is racy issue between smb2 session log off and smb2 session setup.
It will cause user-after-free from session log off.
This add session_lock when setting SMB2_SESSION_EXPIRED and referece
count to session struct not to free session while it is being used.

Cc: stable@vger.kernel.org # v5.15+
Reported-by: zdi-disclosures@trendmicro.com # ZDI-CAN-25282
Signed-off-by: default avatarNamjae Jeon <linkinjeon@kernel.org>
Signed-off-by: default avatarSteve French <stfrench@microsoft.com>
parent 8cf0b939

fs/smb/server/mgmt/user_session.c

+21 −5
Original line number Diff line number Diff line
@@ -177,9 +177,10 @@ static void ksmbd_expire_session(struct ksmbd_conn *conn) 


	down_write(&conn->session_lock);

	xa_for_each(&conn->sessions, id, sess) {

		if (sess->state != SMB2_SESSION_VALID ||

		if (atomic_read(&sess->refcnt) == 0 &&

		    (sess->state != SMB2_SESSION_VALID ||

		     time_after(jiffies,

			       sess->last_active + SMB2_SESSION_TIMEOUT)) {

			       sess->last_active + SMB2_SESSION_TIMEOUT))) {

			xa_erase(&conn->sessions, sess->id);

			hash_del(&sess->hlist);

			ksmbd_session_destroy(sess);
@@ -269,8 +270,6 @@ struct ksmbd_session *ksmbd_session_lookup_slowpath(unsigned long long id) 


	down_read(&sessions_table_lock);

	sess = __session_lookup(id);

	if (sess)

		sess->last_active = jiffies;

	up_read(&sessions_table_lock);



	return sess;
@@ -289,6 +288,22 @@ struct ksmbd_session *ksmbd_session_lookup_all(struct ksmbd_conn *conn, 
	return sess;

}



void ksmbd_user_session_get(struct ksmbd_session *sess)

{

	atomic_inc(&sess->refcnt);

}



void ksmbd_user_session_put(struct ksmbd_session *sess)

{

	if (!sess)

		return;



	if (atomic_read(&sess->refcnt) <= 0)

		WARN_ON(1);

	else

		atomic_dec(&sess->refcnt);

}



struct preauth_session *ksmbd_preauth_session_alloc(struct ksmbd_conn *conn,

						    u64 sess_id)

{
@@ -393,6 +408,7 @@ static struct ksmbd_session *__session_create(int protocol) 
	xa_init(&sess->rpc_handle_list);

	sess->sequence_number = 1;

	rwlock_init(&sess->tree_conns_lock);

	atomic_set(&sess->refcnt, 1);



	ret = __init_smb2_session(sess);

	if (ret)

fs/smb/server/mgmt/user_session.h

+4 −0
Original line number Diff line number Diff line
@@ -61,6 +61,8 @@ struct ksmbd_session { 
	struct ksmbd_file_table		file_table;

	unsigned long			last_active;

	rwlock_t			tree_conns_lock;



	atomic_t			refcnt;

};



static inline int test_session_flag(struct ksmbd_session *sess, int bit)
@@ -104,4 +106,6 @@ void ksmbd_release_tree_conn_id(struct ksmbd_session *sess, int id); 
int ksmbd_session_rpc_open(struct ksmbd_session *sess, char *rpc_name);

void ksmbd_session_rpc_close(struct ksmbd_session *sess, int id);

int ksmbd_session_rpc_method(struct ksmbd_session *sess, int id);

void ksmbd_user_session_get(struct ksmbd_session *sess);

void ksmbd_user_session_put(struct ksmbd_session *sess);

#endif /* __USER_SESSION_MANAGEMENT_H__ */

fs/smb/server/server.c

+2 −0
Original line number Diff line number Diff line
@@ -238,6 +238,8 @@ static void __handle_ksmbd_work(struct ksmbd_work *work, 
	} while (is_chained == true);



send:

	if (work->sess)

		ksmbd_user_session_put(work->sess);

	if (work->tcon)

		ksmbd_tree_connect_put(work->tcon);

	smb3_preauth_hash_rsp(work);

fs/smb/server/smb2pdu.c

+7 −1
Original line number Diff line number Diff line
@@ -605,8 +605,10 @@ int smb2_check_user_session(struct ksmbd_work *work) 


	/* Check for validity of user session */

	work->sess = ksmbd_session_lookup_all(conn, sess_id);

	if (work->sess)

	if (work->sess) {

		ksmbd_user_session_get(work->sess);

		return 1;

	}

	ksmbd_debug(SMB, "Invalid user session, Uid %llu\n", sess_id);

	return -ENOENT;

}
@@ -1740,6 +1742,7 @@ int smb2_sess_setup(struct ksmbd_work *work) 
		}



		conn->binding = true;

		ksmbd_user_session_get(sess);

	} else if ((conn->dialect < SMB30_PROT_ID ||

		    server_conf.flags & KSMBD_GLOBAL_FLAG_SMB3_MULTICHANNEL) &&

		   (req->Flags & SMB2_SESSION_REQ_FLAG_BINDING)) {
@@ -1766,6 +1769,7 @@ int smb2_sess_setup(struct ksmbd_work *work) 
		}



		conn->binding = false;

		ksmbd_user_session_get(sess);

	}

	work->sess = sess;
@@ -2228,7 +2232,9 @@ int smb2_session_logoff(struct ksmbd_work *work) 
	}



	ksmbd_destroy_file_table(&sess->file_table);

	down_write(&conn->session_lock);

	sess->state = SMB2_SESSION_EXPIRED;

	up_write(&conn->session_lock);



	ksmbd_free_user(sess->user);

	sess->user = NULL;