[PATCH 3.19.y-ckt 091/130] iser-target: Fix REJECT CM event use-after-free OOPs

[Kamal Mostafa]

3.19.8-ckt6 -stable review patch.  If anyone has any objections, please let me know.

------------------

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

commit ce9a9fc20a78ad1e5222fae3a83d105f2d2fb9b9 upstream.

This patch fixes a bug in iser-target code where the REJECT CM event
handler code currently performs a isert_put_conn() for the final
isert_conn->kref put, while iscsi_np process context is still blocked
in isert_get_login_rx().

Once isert_get_login_rx() is awoking due to login timeout, iscsi_np
process context will attempt to invoke iscsi_target_login_sess_out()
to cleanup iscsi_conn as expected, and calls isert_wait_conn() +
isert_free_conn() which triggers the use-after-free OOPs.

To address this bug, move the kref_get_unless_zero() call from
isert_connected_handler() into isert_connect_request() immediately
preceeding isert_rdma_accept() to ensure the CM handler cleanup
paths and isert_free_conn() are always operating with two refs.

Cc: Sagi Grimberg <sagig at mellanox.com>
Signed-off-by: Nicholas Bellinger <nab at linux-iscsi.org>
[ kamal: backport to 3.19-stable: context ]
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/infiniband/ulp/isert/ib_isert.c | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/drivers/infiniband/ulp/isert/ib_isert.c b/drivers/infiniband/ulp/isert/ib_isert.c
index b7350d5..bd28c48 100644
--- a/drivers/infiniband/ulp/isert/ib_isert.c
+++ b/drivers/infiniband/ulp/isert/ib_isert.c
@@ -686,6 +686,17 @@ isert_connect_request(struct rdma_cm_id *cma_id, struct rdma_cm_event *event)
 	ret = isert_rdma_post_recvl(isert_conn);
 	if (ret)
 		goto out_conn_dev;
+	/*
+	 * Obtain the second reference now before isert_rdma_accept() to
+	 * ensure that any initiator generated REJECT CM event that occurs
+	 * asynchronously won't drop the last reference until the error path
+	 * in iscsi_target_login_sess_out() does it's ->iscsit_free_conn() ->
+	 * isert_free_conn() -> isert_put_conn() -> kref_put().
+	 */
+	if (!kref_get_unless_zero(&isert_conn->conn_kref)) {
+		isert_warn("conn %p connect_release is running\n", isert_conn);
+		goto out_conn_dev;
+	}
 
 	ret = isert_rdma_accept(isert_conn);
 	if (ret)
@@ -769,11 +780,6 @@ isert_connected_handler(struct rdma_cm_id *cma_id)
 
 	isert_info("conn %p\n", isert_conn);
 
-	if (!kref_get_unless_zero(&isert_conn->conn_kref)) {
-		isert_warn("conn %p connect_release is running\n", isert_conn);
-		return;
-	}
-
 	mutex_lock(&isert_conn->conn_mutex);
 	if (isert_conn->state != ISER_CONN_FULL_FEATURE)
 		isert_conn->state = ISER_CONN_UP;
-- 
1.9.1