[PATCH 4.19 304/639] scsi: target/core: Fix a race condition in the LUN lookup code

[Greg Kroah-Hartman]

From: Bart Van Assche <bvanassche@xxxxxxx>

[ 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@xxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Hannes Reinecke <hare@xxxxxxxx>
Cc: Nicholas Bellinger <nab@xxxxxxxxxxxxxxx>
Fixes: 29a05deebf6c ("target: Convert se_node_acl->device_list[] to RCU hlist") # v4.10
Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
Signed-off-by: Martin K. Petersen <martin.petersen@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/target/target_core_device.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/target/target_core_device.c b/drivers/target/target_core_device.c
index e9ff2a7c0c0e6..22e97a93728db 100644
--- 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;
-- 
2.20.1