scsi: target/core: Fix a race condition in the LUN lookup code

BugLink: https://bugs.launchpad.net/bugs/1863019
[ Upstream commit 63f7479439c95bcd49b7dd4af809862c316c71a3 ]

The rcu_dereference(deve->se_lun) expression occurs twice in the LUN lookup
functions. Since these expressions are not serialized against deve->se_lun
assignments each of these expressions may yield a different result. Avoid
that the wrong LUN pointer is stored in se_cmd by reading deve->se_lun only
once.

Cc: Mike Christie <mchristi@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Nicholas Bellinger <nab@linux-iscsi.org>
Fixes: 29a05deebf6c ("target: Convert se_node_acl->device_list[] to RCU hlist") # v4.10
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/drivers/target/target_core_device.c b/drivers/target/target_core_device.c
index 92b52d2314b5359ed31f1789a874fbed0120cf59..cebef8e5a43d16d61e67ea4a8a58faedebe41e6d 100644 (file)
--- a/drivers/target/target_core_device.c
+++ b/drivers/target/target_core_device.c
@@ -85,7 +85,7 @@ transport_lookup_cmd_lun(struct se_cmd *se_cmd, u64 unpacked_lun)
                        goto out_unlock;
                }
 
-               se_cmd->se_lun = rcu_dereference(deve->se_lun);
+               se_cmd->se_lun = se_lun;
                se_cmd->pr_res_key = deve->pr_res_key;
                se_cmd->orig_fe_lun = unpacked_lun;
                se_cmd->se_cmd_flags |= SCF_SE_LUN_CMD;
@@ -176,7 +176,7 @@ int transport_lookup_tmr_lun(struct se_cmd *se_cmd, u64 unpacked_lun)
                        goto out_unlock;
                }
 
-               se_cmd->se_lun = rcu_dereference(deve->se_lun);
+               se_cmd->se_lun = se_lun;
                se_cmd->pr_res_key = deve->pr_res_key;
                se_cmd->orig_fe_lun = unpacked_lun;
                se_cmd->se_cmd_flags |= SCF_SE_LUN_CMD;