Tablerate->getCsvFile() fails with non-default PHP upload_tmp_dir

[zts]

Preconditions

1. PHP upload_tmp_dir is set to a directory outside /tmp/.
2. Magento CE 2.1.x, code still in latest version here: https://github.com/magento/magento2/blob/develop/app/code/Magento/OfflineShipping/Model/ResourceModel/Carrier/Tablerate.php#L315

Steps to reproduce

1. Make a new directory for uploads, eg mkdir -p /var/lib/php/uploads && chmod 1777 /var/lib/php/uploads
2. Set PHP upload_tmp_dir to this directory. eg, add upload_tmp_dir = /var/lib/php/uploads to /etc/php.ini
3. Login to Magento Admin
4. Go to Stores > Configuration > Sales > Shipping Methods
5. Select Table Rates, and enable
6. Click "Import"
7. Choose a file, click save.

Expected result

1. Table rates are updated

Actual result

1. Receive an error, eg The file “/tmp/var/lib/php/uploads/phphEpJe5” doesn’t exist

Cause

This behaviour occurs because getCsvFile opens the /tmp directory, then looks for the uploaded file relative to that directory. This only works when upload_tmp_directory is set to /tmp, or a subdirectory of /tmp.

[vityakopin]

Internal ticket MAGETWO-70451 was created.

[magento-engcom-team]

@zts, thank you for your report.
We've created internal ticket(s) MAGETWO-70451 to track progress on the issue.