target: fix potential race window in target_sess_cmd_list_waiting()

target_sess_cmd_list_waiting() might hit on a condition where
the kref for the command is already 0, but the destructor has
not been called yet (or is stuck in waiting for a spin lock).
Rather than leaving the command on the list we should explicitly
remove it to avoid race issues later on.

Signed-off-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

diff --git a/drivers/target/target_core_transport.c b/drivers/target/target_core_transport.c
index e825d58..7dfefd6 100644 (file)
--- a/drivers/target/target_core_transport.c
+++ b/drivers/target/target_core_transport.c
@@ -2535,7 +2535,9 @@ int target_get_sess_cmd(struct se_cmd *se_cmd, bool ack_kref)
         * invocations before se_cmd descriptor release.
         */
        if (ack_kref) {
-               kref_get(&se_cmd->cmd_kref);
+               if (!kref_get_unless_zero(&se_cmd->cmd_kref))
+                       return -EINVAL;
+
                se_cmd->se_cmd_flags |= SCF_ACK_KREF;
        }
 
@@ -2616,7 +2618,7 @@ EXPORT_SYMBOL(target_put_sess_cmd);
  */
 void target_sess_cmd_list_set_waiting(struct se_session *se_sess)
 {
-       struct se_cmd *se_cmd;
+       struct se_cmd *se_cmd, *tmp_cmd;
        unsigned long flags;
        int rc;
 
@@ -2628,14 +2630,16 @@ void target_sess_cmd_list_set_waiting(struct se_session *se_sess)
        se_sess->sess_tearing_down = 1;
        list_splice_init(&se_sess->sess_cmd_list, &se_sess->sess_wait_list);
 
-       list_for_each_entry(se_cmd, &se_sess->sess_wait_list, se_cmd_list) {
+       list_for_each_entry_safe(se_cmd, tmp_cmd,
+                                &se_sess->sess_wait_list, se_cmd_list) {
                rc = kref_get_unless_zero(&se_cmd->cmd_kref);
                if (rc) {
                        se_cmd->cmd_wait_set = 1;
                        spin_lock(&se_cmd->t_state_lock);
                        se_cmd->transport_state |= CMD_T_FABRIC_STOP;
                        spin_unlock(&se_cmd->t_state_lock);
-               }
+               } else
+                       list_del_init(&se_cmd->se_cmd_list);
        }
 
        spin_unlock_irqrestore(&se_sess->sess_cmd_lock, flags);