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

From: Kamal Mostafa
Date: Thu Aug 27 2015 - 18:26:35 EST

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


From: Nicholas Bellinger <nab@xxxxxxxxxxxxxxx>

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@xxxxxxxxxxxx>
Signed-off-by: Nicholas Bellinger <nab@xxxxxxxxxxxxxxx>
[ kamal: backport to 3.19-stable: context ]
Signed-off-by: Kamal Mostafa <kamal@xxxxxxxxxxxxx>
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;
- }
if (isert_conn->state != ISER_CONN_FULL_FEATURE)
isert_conn->state = ISER_CONN_UP;

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