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    Subject[PATCH 4.19 304/639] scsi: target/core: Fix a race condition in the LUN lookup code
    Date
    From: Bart Van Assche <bvanassche@acm.org>

    [ 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>
    ---
    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


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