[PATCH] iscsi-target: Fix initial login PDU asynchronous socket close OOPs

Nicholas A. Bellinger
2017-05-26T05:29:59Z

From: Nicholas Bellinger <nab@linux-iscsi.org>

This patch fixes a OOPs originally introduced by:

commit bb048357dad6d604520c91586334c9c230366a14
Author: Nicholas Bellinger <nab@linux-iscsi.org>
Date: Thu Sep 5 14:54:04 2013 -0700

iscsi-target: Add sk->sk_state_change to cleanup after TCP failure

which would trigger a NULL pointer dereference when a TCP connection
was closed asynchronously via iscsi_target_sk_state_change(), but only
when the initial PDU processing in iscsi_target_do_login() from iscsi_np
process context was blocked waiting for backend I/O to complete.

To address this issue, this patch makes the following changes.

First, it introduces some common helper functions used for checking
socket closing state, checking login_flags, and atomically checking
socket closing state + setting login_flags.

Second, it introduces a LOGIN_FLAGS_INITIAL_PDU bit to know when a TCP
connection has dropped via iscsi_target_sk_state_change(), but the
initial PDU processing within iscsi_target_do_login() in iscsi_np
context is still running. For this case, it sets LOGIN_FLAGS_CLOSED,
but doesn't invoke schedule_delayed_work().

The original NULL pointer dereference case reported by MNC is now handled
by iscsi_target_do_login() doing a iscsi_target_sk_check_close() before
transitioning to FFP to determine when the socket has already closed,
or iscsi_target_start_negotiation() if the login needs to exchange
more PDUs (eg: iscsi_target_do_login returned 0) but the socket has
closed. For both of these cases, the cleanup up of remaining connection
resources will occur in iscsi_target_start_negotiation() from iscsi_np
process context once the failure is detected.

Finally, to handle to case where iscsi_target_sk_state_change() is
called after the initial PDU procesing is complete, it now invokes
conn->login_work -> iscsi_target_do_login_rx() to perform cleanup once
existing iscsi_target_sk_check_close() checks detect connection failure.
For this case, the cleanup of remaining connection resources will occur
in iscsi_target_do_login_rx() from delayed workqueue process context
once the failure is detected.

Reported-by: Mike Christie <mchristi@redhat.com>
Cc: Mike Christie <mchristi@redhat.com>
Reported-by: Hannes Reinecke <hare@suse.com>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Sagi Grimberg <sagi@grimberg.me>
Cc: Varun Prakash <varun@chelsio.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
---
drivers/target/iscsi/iscsi_target_nego.c | 194 +++++++++++++++++++++----------
include/target/iscsi/iscsi_target_core.h | 1 +
2 files changed, 133 insertions(+), 62 deletions(-)

diff --git a/drivers/target/iscsi/iscsi_target_nego.c b/drivers/target/iscsi/iscsi_target_nego.c
index 7ccc9c1..6f88b31 100644
--- a/drivers/target/iscsi/iscsi_target_nego.c
+++ b/drivers/target/iscsi/iscsi_target_nego.c
@@ -493,14 +493,60 @@ static void iscsi_target_restore_sock_callbacks(struct iscsi_conn *conn)

static int iscsi_target_do_login(struct iscsi_conn *, struct iscsi_login *);

-static bool iscsi_target_sk_state_check(struct sock *sk)
+static bool __iscsi_target_sk_check_close(struct sock *sk)
{
if (sk->sk_state == TCP_CLOSE_WAIT || sk->sk_state == TCP_CLOSE) {
- pr_debug("iscsi_target_sk_state_check: TCP_CLOSE_WAIT|TCP_CLOSE,"
+ pr_debug("__iscsi_target_sk_check_close: TCP_CLOSE_WAIT|TCP_CLOSE,"
"returning FALSE\n");
- return false;
+ return true;
}
- return true;
+ return false;
+}
+
+static bool iscsi_target_sk_check_close(struct iscsi_conn *conn)
+{
+ bool state = false;
+
+ if (conn->sock) {
+ struct sock *sk = conn->sock->sk;
+
+ read_lock_bh(&sk->sk_callback_lock);
+ state = (__iscsi_target_sk_check_close(sk) ||
+ test_bit(LOGIN_FLAGS_CLOSED, &conn->login_flags));
+ read_unlock_bh(&sk->sk_callback_lock);
+ }
+ return state;
+}
+
+static bool iscsi_target_sk_check_flag(struct iscsi_conn *conn, unsigned int flag)
+{
+ bool state = false;
+
+ if (conn->sock) {
+ struct sock *sk = conn->sock->sk;
+
+ read_lock_bh(&sk->sk_callback_lock);
+ state = test_bit(flag, &conn->login_flags);
+ read_unlock_bh(&sk->sk_callback_lock);
+ }
+ return state;
+}
+
+static bool iscsi_target_sk_check_and_clear(struct iscsi_conn *conn, unsigned int flag)
+{
+ bool state = false;
+
+ if (conn->sock) {
+ struct sock *sk = conn->sock->sk;
+
+ write_lock_bh(&sk->sk_callback_lock);
+ state = (__iscsi_target_sk_check_close(sk) ||
+ test_bit(LOGIN_FLAGS_CLOSED, &conn->login_flags));
+ if (!state)
+ clear_bit(flag, &conn->login_flags);
+ write_unlock_bh(&sk->sk_callback_lock);
+ }
+ return state;
}

static void iscsi_target_login_drop(struct iscsi_conn *conn, struct iscsi_login *login)
@@ -540,6 +586,20 @@ static void iscsi_target_do_login_rx(struct work_struct *work)

pr_debug("entering iscsi_target_do_login_rx, conn: %p, %s:%d\n",
conn, current->comm, current->pid);
+ /*
+ * If iscsi_target_do_login_rx() has been invoked by ->sk_data_ready()
+ * before initial PDU processing in iscsi_target_start_negotiation()
+ * has completed, go ahead and retry until it's cleared.
+ *
+ * Otherwise if the TCP connection drops while this is occuring,
+ * iscsi_target_start_negotiation() will detect the failure, call
+ * cancel_delayed_work_sync(&conn->login_work), and cleanup the
+ * remaining iscsi connection resources from iscsi_np process context.
+ */
+ if (iscsi_target_sk_check_flag(conn, LOGIN_FLAGS_INITIAL_PDU)) {
+ schedule_delayed_work(&conn->login_work, msecs_to_jiffies(10));
+ return;
+ }

spin_lock(&tpg->tpg_state_lock);
state = (tpg->tpg_state == TPG_STATE_ACTIVE);
@@ -547,26 +607,12 @@ static void iscsi_target_do_login_rx(struct work_struct *work)

if (!state) {
pr_debug("iscsi_target_do_login_rx: tpg_state != TPG_STATE_ACTIVE\n");
- iscsi_target_restore_sock_callbacks(conn);
- iscsi_target_login_drop(conn, login);
- iscsit_deaccess_np(np, tpg, tpg_np);
- return;
+ goto err;
}

- if (conn->sock) {
- struct sock *sk = conn->sock->sk;
-
- read_lock_bh(&sk->sk_callback_lock);
- state = iscsi_target_sk_state_check(sk);
- read_unlock_bh(&sk->sk_callback_lock);
-
- if (!state) {
- pr_debug("iscsi_target_do_login_rx, TCP state CLOSE\n");
- iscsi_target_restore_sock_callbacks(conn);
- iscsi_target_login_drop(conn, login);
- iscsit_deaccess_np(np, tpg, tpg_np);
- return;
- }
+ if (iscsi_target_sk_check_close(conn)) {
+ pr_debug("iscsi_target_do_login_rx, TCP state CLOSE\n");
+ goto err;
}

conn->login_kworker = current;
@@ -584,34 +630,29 @@ static void iscsi_target_do_login_rx(struct work_struct *work)
flush_signals(current);
conn->login_kworker = NULL;

- if (rc < 0) {
- iscsi_target_restore_sock_callbacks(conn);
- iscsi_target_login_drop(conn, login);
- iscsit_deaccess_np(np, tpg, tpg_np);
- return;
- }
+ if (rc < 0)
+ goto err;

pr_debug("iscsi_target_do_login_rx after rx_login_io, %p, %s:%d\n",
conn, current->comm, current->pid);

rc = iscsi_target_do_login(conn, login);
if (rc < 0) {
- iscsi_target_restore_sock_callbacks(conn);
- iscsi_target_login_drop(conn, login);
- iscsit_deaccess_np(np, tpg, tpg_np);
+ goto err;
} else if (!rc) {
- if (conn->sock) {
- struct sock *sk = conn->sock->sk;
-
- write_lock_bh(&sk->sk_callback_lock);
- clear_bit(LOGIN_FLAGS_READ_ACTIVE, &conn->login_flags);
- write_unlock_bh(&sk->sk_callback_lock);
- }
+ if (iscsi_target_sk_check_and_clear(conn, LOGIN_FLAGS_READ_ACTIVE))
+ goto err;
} else if (rc == 1) {
iscsi_target_nego_release(conn);
iscsi_post_login_handler(np, conn, zero_tsih);
iscsit_deaccess_np(np, tpg, tpg_np);
}
+ return;
+
+err:
+ iscsi_target_restore_sock_callbacks(conn);
+ iscsi_target_login_drop(conn, login);
+ iscsit_deaccess_np(np, tpg, tpg_np);
}

static void iscsi_target_do_cleanup(struct work_struct *work)
@@ -659,31 +700,54 @@ static void iscsi_target_sk_state_change(struct sock *sk)
orig_state_change(sk);
return;
}
+ state = __iscsi_target_sk_check_close(sk);
+ pr_debug("__iscsi_target_sk_close_change: state: %d\n", state);
+
if (test_bit(LOGIN_FLAGS_READ_ACTIVE, &conn->login_flags)) {
pr_debug("Got LOGIN_FLAGS_READ_ACTIVE=1 sk_state_change"
" conn: %p\n", conn);
+ if (state)
+ set_bit(LOGIN_FLAGS_CLOSED, &conn->login_flags);
write_unlock_bh(&sk->sk_callback_lock);
orig_state_change(sk);
return;
}
- if (test_and_set_bit(LOGIN_FLAGS_CLOSED, &conn->login_flags)) {
+ if (test_bit(LOGIN_FLAGS_CLOSED, &conn->login_flags)) {
pr_debug("Got LOGIN_FLAGS_CLOSED=1 sk_state_change conn: %p\n",
conn);
write_unlock_bh(&sk->sk_callback_lock);
orig_state_change(sk);
return;
}
+ /*
+ * If the TCP connection has dropped, go ahead and set LOGIN_FLAGS_CLOSED,
+ * but only queue conn->login_work -> iscsi_target_do_login_rx()
+ * processing if LOGIN_FLAGS_INITIAL_PDU has already been cleared.
+ *
+ * When iscsi_target_do_login_rx() runs, iscsi_target_sk_check_close()
+ * will detect the dropped TCP connection from delayed workqueue context.
+ *
+ * If LOGIN_FLAGS_INITIAL_PDU is still set, which means the initial
+ * iscsi_target_start_negotiation() is running, iscsi_target_do_login()
+ * via iscsi_target_sk_check_close() or iscsi_target_start_negotiation()
+ * via iscsi_target_sk_check_and_clear() is responsible for detecting the
+ * dropped TCP connection in iscsi_np process context, and cleaning up
+ * the remaining iscsi connection resources.
+ */
+ if (state) {
+ pr_debug("iscsi_target_sk_state_change got failed state\n");
+ set_bit(LOGIN_FLAGS_CLOSED, &conn->login_flags);
+ state = test_bit(LOGIN_FLAGS_INITIAL_PDU, &conn->login_flags);
+ write_unlock_bh(&sk->sk_callback_lock);

- state = iscsi_target_sk_state_check(sk);
- write_unlock_bh(&sk->sk_callback_lock);
-
- pr_debug("iscsi_target_sk_state_change: state: %d\n", state);
+ orig_state_change(sk);

- if (!state) {
- pr_debug("iscsi_target_sk_state_change got failed state\n");
- schedule_delayed_work(&conn->login_cleanup_work, 0);
+ if (!state)
+ schedule_delayed_work(&conn->login_work, 0);
return;
}
+ write_unlock_bh(&sk->sk_callback_lock);
+
orig_state_change(sk);
}

@@ -946,6 +1010,15 @@ static int iscsi_target_do_login(struct iscsi_conn *conn, struct iscsi_login *lo
if (iscsi_target_handle_csg_one(conn, login) < 0)
return -1;
if (login_rsp->flags & ISCSI_FLAG_LOGIN_TRANSIT) {
+ /*
+ * Check to make sure the TCP connection has not
+ * dropped asynchronously while session reinstatement
+ * was occuring in this kthread context, before
+ * transitioning to full feature phase operation.
+ */
+ if (iscsi_target_sk_check_close(conn))
+ return -1;
+
login->tsih = conn->sess->tsih;
login->login_complete = 1;
iscsi_target_restore_sock_callbacks(conn);
@@ -972,21 +1045,6 @@ static int iscsi_target_do_login(struct iscsi_conn *conn, struct iscsi_login *lo
break;
}

- if (conn->sock) {
- struct sock *sk = conn->sock->sk;
- bool state;
-
- read_lock_bh(&sk->sk_callback_lock);
- state = iscsi_target_sk_state_check(sk);
- read_unlock_bh(&sk->sk_callback_lock);
-
- if (!state) {
- pr_debug("iscsi_target_do_login() failed state for"
- " conn: %p\n", conn);
- return -1;
- }
- }
-
return 0;
}

@@ -1255,10 +1313,22 @@ int iscsi_target_start_negotiation(

write_lock_bh(&sk->sk_callback_lock);
set_bit(LOGIN_FLAGS_READY, &conn->login_flags);
+ set_bit(LOGIN_FLAGS_INITIAL_PDU, &conn->login_flags);
write_unlock_bh(&sk->sk_callback_lock);
}
-
+ /*
+ * If iscsi_target_do_login returns zero to signal more PDU
+ * exchanges are required to complete the login, go ahead and
+ * clear LOGIN_FLAGS_INITIAL_PDU but only if the TCP connection
+ * is still active.
+ *
+ * Otherwise if TCP connection dropped asynchronously, go ahead
+ * and perform connection cleanup now.
+ */
ret = iscsi_target_do_login(conn, login);
+ if (!ret && iscsi_target_sk_check_and_clear(conn, LOGIN_FLAGS_INITIAL_PDU))
+ ret = -1;
+
if (ret < 0) {
cancel_delayed_work_sync(&conn->login_work);
cancel_delayed_work_sync(&conn->login_cleanup_work);
diff --git a/include/target/iscsi/iscsi_target_core.h b/include/target/iscsi/iscsi_target_core.h
index 275581d..5f17fb7 100644
--- a/include/target/iscsi/iscsi_target_core.h
+++ b/include/target/iscsi/iscsi_target_core.h
@@ -557,6 +557,7 @@ struct iscsi_conn {
#define LOGIN_FLAGS_READ_ACTIVE 1
#define LOGIN_FLAGS_CLOSED 2
#define LOGIN_FLAGS_READY 4
+#define LOGIN_FLAGS_INITIAL_PDU 8
unsigned long login_flags;
struct delayed_work login_work;
struct delayed_work login_cleanup_work;
--
1.9.1