linux-kernel - Re: [PATCHv3 1/2] mm/gup: fix omission of check on FOLL_LONGTERM in get_user_pages

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Message-Id: <87tvcwhzdo.fsf@linux.ibm.com>
Date:   Tue, 11 Jun 2019 21:45:31 +0530
From:   "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
To:     Pingfan Liu <kernelfans@...il.com>, linux-mm@...ck.org
Cc:     Pingfan Liu <kernelfans@...il.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Matthew Wilcox <willy@...radead.org>,
        John Hubbard <jhubbard@...dia.com>,
        Keith Busch <keith.busch@...el.com>,
        Christoph Hellwig <hch@...radead.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCHv3 1/2] mm/gup: fix omission of check on FOLL_LONGTERM in get_user_pages_fast()

Pingfan Liu <kernelfans@...il.com> writes:

> As for FOLL_LONGTERM, it is checked in the slow path
> __gup_longterm_unlocked(). But it is not checked in the fast path, which
> means a possible leak of CMA page to longterm pinned requirement through
> this crack.

Shouldn't we disallow FOLL_LONGTERM with get_user_pages fastpath? W.r.t
dax check we need vma to ensure whether a long term pin is allowed or not.
If FOLL_LONGTERM is specified we should fallback to slow path.

-aneesh