[PATCH V2 3/3] target: iscsi: prevent login threads from racing between each other

[Maurizio Lombardi <mlombard@redhat.com>]

The tpg->np_login_sem is a semaphore that is used to serialize the login
process when multiple login threads run concurrently against the same
target portal group.

The iscsi_target_locate_portal() function finds the tpg,
calls iscsit_access_np() against the np_login_sem semaphore
and saves the tpg pointer in conn->tpg;

If iscsi_target_locate_portal() fails, the caller will check for the
conn->tpg pointer and, if it's not NULL, then it will assume
that iscsi_target_locate_portal() called iscsit_access_np() on the
semaphore.

Make sure that conn->tpg gets initialized only if iscsit_access_np()
was successful, otherwise iscsit_deaccess_np() may end up
being called against a semaphore we never took, allowing more than one
thread to access the same tpg.

Signed-off-by: Maurizio Lombardi <mlombard@redhat.com>
---
 drivers/target/iscsi/iscsi_target_nego.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/target/iscsi/iscsi_target_nego.c b/drivers/target/iscsi/iscsi_target_nego.c
index 4164977c170e..9b0c1196fe8e 100644
--- a/drivers/target/iscsi/iscsi_target_nego.c
+++ b/drivers/target/iscsi/iscsi_target_nego.c
@@ -1121,6 +1121,7 @@ int iscsi_target_locate_portal(
 	iscsi_target_set_sock_callbacks(conn);
 
 	login->np = np;
+	conn->tpg = NULL;
 
 	login_req = (struct iscsi_login_req *) login->req;
 	payload_length = ntoh24(login_req->dlength);
@@ -1188,7 +1189,6 @@ int iscsi_target_locate_portal(
 	 */
 	sessiontype = strncmp(s_buf, DISCOVERY, 9);
 	if (!sessiontype) {
-		conn->tpg = iscsit_global->discovery_tpg;
 		if (!login->leading_connection)
 			goto get_target;
 
@@ -1205,9 +1205,11 @@ int iscsi_target_locate_portal(
 		 * Serialize access across the discovery struct iscsi_portal_group to
 		 * process login attempt.
 		 */
+		conn->tpg = iscsit_global->discovery_tpg;
 		if (iscsit_access_np(np, conn->tpg) < 0) {
 			iscsit_tx_login_rsp(conn, ISCSI_STATUS_CLS_TARGET_ERR,
 				ISCSI_LOGIN_STATUS_SVC_UNAVAILABLE);
+			conn->tpg = NULL;
 			ret = -1;
 			goto out;
 		}
-- 
2.31.1