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SELECT FOR UPDATE on a view should require UPDATE (as well as SELECT) permissions on the view, and then the view's owner needs those same permissions against the relations it references, and so on all the way down to base tables. But ApplyRetrieveRule did things in the wrong order, resulting in failure to mark intermediate view levels as needing UPDATE permission. Thus for example, if user A creates a table T and an updatable view V1 on T, then grants only SELECT permissions on V1 to user B, B could create a second view V2 on V1 and then would be allowed to perform SELECT FOR UPDATE via V2 (since V1 wouldn't be checked for UPDATE permissions). To fix, just switch the order of expanding sub-views and marking referenced objects as needing UPDATE permission. I think additional simplifications are now possible, but that's distinct from the bug fix proper. This is certainly a security issue, but the consequences are pretty minor (just the ability to lock rows that shouldn't be lockable). Against that we have a small risk of breaking applications that are working as-desired, since nested views have behaved this way since such cases worked at all. On balance I'm inclined not to back-patch. Per report from Alexander Lakhin. Discussion: https://postgr.es/m/24db7b8f-3de5-e25f-7ab9-d8848351d42c@gmail.com
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